rmMmmw#* fcNHpLTHPRI)* 1880 ^s^^^^^^^^^^^^^^^fe.%,^.S^^^^^^^^^^^^ !i ■'/S///W > Copyright. LINDSAY & BLAKISTON. 1879. CONTENTS. CHAPTER I. Introduction .... 9 CHAPTER II. The Anatomy of the Eye CHAPTER III The Physiology of Vision CHAPTER IV. The Ophthalmoscope......46 CHAPTER V. Injuries and Diseases of the Eye . . .49 CHAPTER VI. Optical Defects .• . . .' . . .68 vii 12 3* Vlll CONTENTS. CHAPTER VII. „, PAGE Spectacles ........g6 CHAPTER VIII. Practical Suggestions for the Care of the Eyes.........io4 CHAPTER IX. Effects of School-Life upon the Sight . .120 EYESIGHT, AND HOW TO CARE FOR IT. CHAPTER I. INTRODUCTION. THE subject selected for this number of the series is a wide one. Involving, as it does, the sciences of anatomy, physiology, and optics, it has enlisted earnest and distinguished workers from all, and has accumulated a literature of its own which an ordi- nary lifetime is hardly long enough to master. It is not without a certain sense of absurdity in the un- dertaking, that an attempt is made to crowd such a subject into so small a space; but it will, of course, be understood that nothing more is intended than a su- perficial and hasty glance at its general outlines. The object will be to place before the reader such ele- mentary knowledge as is necessary to enable him to understand the conditions under which the eyes must 9 IO EYESIGHT, AND HOW TO CARE FOR IT. do their work; and to place this knowledge within the reach of all, the explanations will be made as simple as possible, and the use of " technical lan- guage," that lion so much dreaded in the path of the general reader, will be carefully avoided. That an intelligent care of the eyesight requires some knowledge of the structure and functions of the organ of vision, is a proposition too plain to admit of argument. Even aside from utilitarian considera- tions, indeed, one would suppose that a subject so important and so full of intrinsic interest would have irresistible attractions for every cultivated and inquir- ing mind; but the experience of the ophthalmic sur- geon, in his daily practice, forces upon him the con- viction that this is far from being the case, and that for most people, outside of the medical profession, the anatomy and physiology of the eye, and the sim- plest laws of optics that apply to it, are practically a sealed book. Nor has this much abused organ had fairer play in practical use than in theoretical knowledge, for many who would give to tired limbs or back the needed rest, or nurse a lame leg with the most tender care, will goad on their willing but disabled or overstrained eyes in the most reckless way. Whatever practical hints may be given will have reference to prevention rather than cure. The former is within the province of common sense, guided by INTR OD UCTION. 11 such general knowledge as every person of good edu- cation should have; while the first requisite for the latter is the ability to determine what is to be cured, in other words, the power of forming a correct diag- nosis, which can come only by special study and care- ful training. The lawyers have a saying that "the man who pleads his own case has a fool for a client;'' and many and sad results are met with in proof of the fact that the man who undertakes to "doctor" his own eyes has a patient who is far from wise, and who runs a great risk of being very unfortunate; but no- where is an ounce of prevention more certainly worth many pounc'o of cure, and all may avoid subjecting the organ upon which our labors and our pleasures so essentially depend to unnecessary peril by careless- ness, imprudence, or want of knowledge. In an effort merely to popularize established facts and accepted theories which have become the com- mon property of scientific men, it will, of course, be understood that no originality is claimed, and it will not be necessary to weary the reader with reference to authorities. CHAPTER II. THE ANATOMY OF THE EYE. IN the small space occupied by the eye and its ap- pendages, all the anatomical elements of the body are represented, arranged with a delicate adjustment to each other, and an exquisite adaptation of every part to the great object of the whole, that render this little organ one of the greatest wonders in Nature. Of course, no attempt can be made here to enter into nice details, but only to give a general idea of the anatomical structure. The eyeball is nearly spherical in form and about an inch in diameter. For convenience of description, it is sometimes spoken of as consisting of three mem- branes, or coats, and three humors. The external or fibrous coat is a firm, tough membrane, having almost the resistance of leather, and is about one twenty-fourth of an inch thick. It maintains the form of the ball, fur- nishes attachments to the external muscles that move it, and protects its delicate contents. The sclerotic (Fig. I., i), which includes the posterior four-fifths of this coat, is opaque, and forms what is known as the "white 12 THE ANATOMY OF THE EYE. 13 of the eye;" the anterior one-fifth, the cornea (Fig. I., 4) is transparent, arid is joined to the sclerotic somewhat as a watch-glass is set in its case. On ac- Fig. I.—Vertical Section of the Eyeball. I. Sclerotic; 2. Choroid; 3. Ciliary muscle; 4. Cornea; 5. Iris ; 6. Aqueous humor ; 7. Lens ; 8. Vitreous humor ; 9. Retina ; 10. Optic nerve. count of its transparency, the cornea can be best seen by looking at it from the side, or by observing the reflection of a window-sash upon its surface ; we usu- ally look directly through it and see only the colored iris behind it. The next coat, called the vascular because it con- tains most of the blood-vessels of the eyeball, com- prises the choroid and iris. The choroid lies against 2 14 EYESIGHT, AND HOW TO CARE FOR IT. the inner surface of the sclerotic, and the iris forms a curtain behind the cornea. Fig. II.— Iris, Ciliary Muscle, and Choroid. The Whole of the Cornea and Part of the Sclerotic have been Removed. i. Pupil; 2. Iris; 3. Ciliary muscle; 4. Choroid; 5. Ciliary nerves; 6. Re- mainder of Sclerotic ; 7. Optic nerve. {After Gray.) The choroid (Figs. L, 2, and II., 4) consists princi- pally of a net-work of blood-vessels lined with a layer of flat, dark brown, or nearly black, pigment cells, which also covers the posterior surface of the iris. The use of this dark surface is to absorb the excess of light, which, THE ANATOMY OF THE EYE. 15 by reflection and diffusion, would prevent accurate vision. The iris (Figs. I., 5, and II., 2) forms a curtain stretched across the interior of the eye, behind the cornea, at the margin of which it is attached. It is the iris that gives to the eye its special color, and upon which its beauty, to a great ex- tent, depends. When we speak of a blue, brown, hazel, or black eye, we mean that this is the color of the iris — hence the name of iris, or " rainbow." The original color of the iris is blue, and depends not upon a pigment, or coloring matter, but upon what opticians call an " interference phenomenon," — that is, it is the result of the effect upon each other of waves of light reflected back and forth from the minute irregularities of its surface,— and the perma- nent hue is formed by the addition of a greater or less amount of dark pigment. The color of the iris is usually in accord with the general coloring of the in- dividual, so that we have every variety of shade, from the black of the negro through the dark brown of the brunette, and the gray or blue of the blonde to the colorless iris of the albino. The eyes of albinos are pink, not from the color of the iris, but from the re- flection seen thro.ugh it, from the red blood in the vessels of the choroid in which also pigment is absent. A good example of this kind of eye may be seen in the white rabbit. The pink eyes, transparent skin, 16 EYESIGHT, AND HOW TO CARE FOR IT. and snow-white hair of true albinos give them a most peculiar appearance. Their sight is always deficient, and they are painfully sensitive to light, against an excess of which they have not the natural protection. It is not generally known that the eyes of infants are always blue, and that they do not begin to assume their permanent color until the sixth or eighth week. There is therefore truth, as well as poetry, in the statement that babies look about them " in blue-eyed wonder.'' The wonder may be left to poets and phil- osophers, but the blue is always a practical fact. It is not uncommon to see different colors in the eyes of the same person, and even in the same eye half of the iris is sometimes brown and the other half blue. There is a popular notion that dark eyes are stronger than light ones. There is no truth in this except so far as they are better protected against excessive light; hence, light eyes prevail among northern nations and dark eyes among the races who live in the glare of a tropical sun. Near the centre of the iris is a round opening, the pupil (Fig. II., i), through which all the light that en- ters the back part of the eye must pass. Through the action of two sets of muscles in the iris, one circular and the other radiating, the pupil has the property of contracting and dilating, and its function is to regulate the amount of light admitted to the retina. When we pass from a dark room to a brightly lighted one, the pupil contracts, to protect the eye from the irrita- THE ANATOMY OF THE EYE. IJ ting glare of a flood of light; and when we pass into the dark it dilates, to admit as much of the insufficient light as possible. Belladonna applied to the eye, or taken to excess internally, dilates the pupil, and Cala- bar bean contracts it to a pinhole. Opium also contracts it, and this is the first symptom looked for when opium poisoning is suspected. When we look at a distance, or when the eyes are not directed to any object, as in meditation, the pupils dilate ; and this pensive ex- pression is said to be sometimes imitated by the use of belladonna. A light eye is also made to appear dark in this way, and the expression of the face is very much changed. The pupil is much smaller in the old than in the young, and this partially compen- sates for one of the optical defects incident to age. The shape of the pupil varies in different animals ; in the cat, for instance, it is a long, narrow slit when contracted, and round when dilated. In the huTnan eye, the pupil appears black; but in the eyes of certain animals it presents, in obscure light, a bright glare, which, even when seen in the cat, sometimes makes superstitious or nervous people uncomfortable, and must add not a little to the ter- rors of a lion or tiger ready to spring upon his prey. Before the present century, this was thought to be a kind of phosphorescent emanation from the retina, and to glitter more brightly when the animal was excited; but it is now known to be merely a reflection 2* B 18 EYESIGHT, AND HOW TO CARE FOR IT. from a bright patch of metallic lustre, found upon the choroid of these animals, called the tapetum lucidum. At the junction of the iris and choroid is found a narrow band of delicate muscular fibres, called the ciliary muscle, (Figs. I., 3, and II., 3.) This little muscle has a very interesting and important function, which will be referred to later. The retina, the third or nervous membrane, (Fig. I., 9) is the most important of all; indeed, all the other structures of the eye may be considered sub- servient to this one, for on it are formed the images of external objects, by means of which we are said to see them. It is a very complicated and extremely delicate structure, offering endless difficulties to the investigator; and, though an immense amount of labor has been expended upon it by many masters in science, its minute anatomy can hardly yet be con- sidered settled. Though its greatest thickness does not exceed one one-hundred-and-twentiefh of an inch, microscopists have described some eight or ten differ- ent layers, only two of which it will be necessary, for our present purpose, to refer to. The external is sometimes spoken of as the percipient layer, because it receives the images of objects and produces a sen- sation which is conveyed to the brain, telegraphed, as it were, by the fibres of the internal or conductive layer. This external layer, called Jacob's membrane, is shown by the microscope to consist of minute THE ANATOMY OF THE EYE. 19 columns arranged side by side perpendicular to the choroid, while the internal, or nerve-fibre layer, is composed of delicate nerve-fibrils forming a surface parallel to the choroid. A number of the little col- umns connect with each nerve-fibril, and the fibrils collect into a bundle which passes through the scle- rotic at the back of the eye and, receiving a strong sheath, forms the optic nerve. The optic nerve (Figs. I., 10, and II., 7) passes from the eye to the brain. In this way all the columns of the external layer of the retina are brought into direct communication with the brain, and may be almost said to feel the retinal image, just as the papillae of touch in our fingers feel any object with which they are brought in contact. As each kind of nerve responds to a special sensa- tion, and has no concern with any other, the optic nerve can convey no other impression than that of light, and can no more conduct a sensation of pain than a nerve of ordinary sensation can see; hence, when irritated, as by galvanism, it responds by a flash of light. When the retina is irritated by the concussion of a violent blow, the flashes of light that result have given rise to the expression of "seeing stars." Disease of the retina or optic nerve fre- quently destroys sight entirely without exciting the slightest pain. The three humors are the aqueous, crystalline, and vitreous. 20 EYESIGHT, AND HOW TO CARE FOR IT. • The vitreous humor (Fig. I. ,8) occupies four-fifths of the interior of the ball. It is colorless and transparent, and has rather less consistence than gelatine jelly. It is admirably adapted to maintain the form of the eyeball and give to the retina, which is spread upon its outer surface, the necessary support, while, at the same time, it yields sufficiently to protect this delicate structure from injury by jarring or external pressure. The eye is a wonderful example of skilful packing, combining firmness, elasticity, compactness, mobility and safety in a degree of perfection that can never be approached by art, and is perhaps scarcely equalled elsewhere in Nature. The crystalline humor, or lens (Fig. I., 7), is firmer than the vitreous, but not solid, and is shaped much like a double convex lens or ordinary "magnifying glass." Its form is maintained by a thin, transparent, elastic capsule, and in young persons its consistence is such as to allow its convexity to be readily altered. It grows denser by age, which is the cause of '' old- sight ; " when it is no longer possible to increase the convexity of the lens, a convex spectacle glass must be used for near vision. The lens rests in a cup- shaped cavity in front of the vitreous, and is therefore just behind the iris, with its centre opposite the pupil. The aqueous humor (Fig I., 6) is nearly pure water, and is contained in the space between the cornea and lens. The eyeball is imbedded in a soft cushion of oily THE ANATOMY OF THE EYE. 21 fat, which supports and protects it, and, at the same time, allows it to move in all directions as freely as if it floated in water. The orbit, in which the ball is lodged, is a hollow cone of bone with the base directed forwards and out- wards. The external edge of the orbit extends much less forwards than the internal, and the axes of the two orbits, if followed back, would meet at an angle of 450 ; an arrangement which permits the widest lateral range of vision consistent with the power of directing both eyes at the same time to a near object — that is, the faculty of binocular vision. The posi- tion of the orbits varies much in- different animals; in some, whose chance in the struggle for existence depends more on flight than on defence, the eyes are placed so entirely at the side of the head that they can see almost as well behind them as in front. They have a wide range of vision, but have not the ability to di- rect both eyes to the same object. This arrangement is very marked in the giraffe, whose eyes we can see almost as well when we stand behind him as we can in front. The edges of the orbit are comparatively dense and strong, particularly the upper one, which overhangs the eye, and is capable of shielding it from a very powerful blow; as is frequently attested by what is known as a "black eye," when the surrounding tis- sues are swollen and inflamed and filled with blood, while the eye peeps through them quite unharmed. 22 EYESIGHT, AND HOW TO CARE FOR IT. When the eyeball itself is injured by the fist, it is always by a blow aimed from beneath. The case is different with the deeper part of the orbit, the roof of which is formed of a plate of bone scarcely thicker than parchment. The front portion of the brain rests upon this bone, and has frequently been fatally wounded by injuries involving it. Duelists have sometimes selected the roof of the orbit as a vulnerable spot for a sword-thrust, and Henry II., of France, was accidentally killed at a tournament by a lance-point that pierced his brain through this fragile bone. The eyebrows are formed of muscle and thick skin, covered with stiff hairs, and resting on a bony ridge above the edge of the orbit. The hairs are arranged somewhat like the straw on a thatched roof, and shed the perspiration that trickles down the forehead. An- other useful purpose is shown by the way in which they are instantly drawn down when we are suddenly exposed to a dazzling light. They have aesthetic , functions, too, as powerful organs of expression. A frown is produced by wrinkling and depressing the brows, while by elevating them we can express in- credulity, surprise, or contempt almost as plainly as by words. The word supercilious is derived from su- percilium, the Latin term for eyebrow. The eyebrows may be considered almost distinctive in man; the seal has a few stiff hairs, and in some birds, as the THE ANATOMY -OF THE EYE. 2$ falcon, they are represented by an arrangement of the feathers above the eye ; but even our supposed imme- diate progenitors, the monkeys, cannot lay claim to them. The eyelid is covered with thin, loose skin and lined with smooth and delicate mucous membrane, and be- tween these is a plate of cartilage, to give it shape and firmness, and the muscles that move it. The upper lid, which is much the larger, is very movable, while the lower one is almost stationary. It results, from this disproportion in size, that when the eye is closed, the pupil is completely covered by the upper lid, and is much better protected than it would be if opposite to the fissure between them. An additional protection is afforded during sleep, or when the eye is threatened with violence, by a rolling upward of the ball. The skin of the lids contains no fat; a fortunate pro- vision, for if fat increased there as it sometimes does in the rest of the body, the eye would be mechanically closed. This mechanical blindness often results from swelling of the lids by injury or disease. Patients with erysipelas of the face are frequently much alarmed to find themselves completely blind; but it is consoling to know that the disease very rarely extends to the eye itself. The thin and delicate skin of the lower lid, loosely attached to the tissues beneath, furnishes valuable indications of the state of the circulation. 24 EYESIGHT, AND HOW TO CARE FOR IT. A puffiness and a dark shade under the eye show a sluggishness in the flow of the blood, and a more de- cided swelling is one of the first symptoms of some kinds of dropsy. The lids lie gently upon the eye, and are maintained in accurate contact with it by atmospheric pressure. The two surfaces move against each other with perfect freedom, and with an entire unconsciousness of friction, which the presence of the minutest particle of dust, or even a congestion of the blood-vessels, will at once disturb. This free- dom from friction depends not only upon the smoothness of the surfaces and their exquisite adap- tation to each other, but they are lubricated by a secretion of mucus from the conjunctiva, and moist- ened by a constant flow of tears. The polish and transparency of the cornea are maintained by fre- quent unconscious winking, which keeps its surface moist and free from dust. When the muscle that closes the lids is paralyzed, the cornea soon becomes hazy and dim, and blindness sometimes results. A number of small glands that open near the roots of the lashes keep the edges of the lids greased with an oily secretion which impedes the overflow of tears. This effect may be seen by greasing the edges of a cup, and then filling it with water, when it will be found that the surface of the water can be raised to a higher level than the edges of the cup. The lashes have a decided curve, whose convexity is downward THE ANATOMY OF THE EYE. 2$ in the upper set and upward in the lower, and when the lids are partially closed, they interlace in such a way as to form a screen, which, without excluding vision, serves as an admirable protection against wind and dust or excessive light. As their bulbs are freely supplied with nerves, they are delicately sensi- tive to the slightest touch, and act as "feelers" to warn the eye of the approach of any small object, as an insect, in the dark, or when the vision is not on guard. They differ from other hairs, in being thickest in the middle and tapering towards each end, and undergo a constant renewal; each one reaches ma- turity in about five months, and then drops out, and is succeeded by a fresh one. When this process is interfered with by inflammation of the edge of the lid, the new lashes sometimes take a wrong direction, and turn their points against the eyeball. They are then popularly called "wild hairs," and not only cause intense discomfort, but may inflict serious injury. It is quite a common mistake to attribute an irri- tation from some other cause to "wild hairs," and many persons pull out their lashes with great perse- verance and patience, but without the slightest prov- ocation. The mucous membrane of the eye is continuous with the skin at the margin of the lids. After lining the inner surface of the lids, it passes over to the ball, forming a loose fold, which is the only direct con- 3 26 EYESIGHT, AND HOW TO CARE FOR IT. nection between them; hence its name, conjunctiva. It covers the front part of the sclerotic, the whole of the visible portion, and, lining the walls of the tear- duct, becomes continuous with the mucous mem- brane of the nose and throat, and, therefore, usually takes a part in a "cold in the head," or influenza. It is ordinarily nearly white, with, perhaps, a few of the larger blood-vessels seen winding through it, but is very easily congested by local injury, or inflam- mation, or by general disturbances of the circulation, particularly of the head, as in the case of the " blood- shot '' eye that tells of a debauch. The characteristic yellow tinge of the eye in jaundice is due to the coloring matter of bile deposited in the conjunctiva. The opening between the lids is called the commis- sure, and the apparent size of the eye depends chiefly upon the width of this space. The actual size of the eye varies comparatively little in different individuals, but some eyes appear much larger than others, be- cause the lids are more widely opened. When an inflamed eye is kept constantly partially closed from an excessive sensitiveness to light, much anxiety is often caused by the conviction that it is becoming smaller. The almond shape of the Eastern beauty's eye de- pends upon the length of the fissure between the lids, and its effect is sometimes imitated by prolonging the shadow at the outer angle of the commissure with THE ANATOMY OF THE EYE. a few touches of the "cosmetic pencil." In the Chinese, the outer angle of the commissure is much higher than the inner, giving the cleft an obliquity upwards and outwards. (Fig. III.) This has a very marked effect upon the ex- pression of the face, which, at least to Caucasian taste, is always sinister; the pic- tures of Mephistopheles owe much of their devilish cast to the twitching upwards of the external angles of the lids. It is a curious illus- tration of the natural prej- udice in favor of our own peculiarities, that in Chinese caricatures of the " Meli- can man " the outer angles of the eyelids are absurdly drawn downwards. A drooping lid gives the impression of weakness or fatigue, and, in the final stages of wasting fevers, the half-closed eye, concealing the cornea and iris and exposing only the white sclerotic, has a pain- fully ghastly effect, and is a most discouraging symp- tom. The lachrymal apparatus (Fig. IV.) consists of the gland for secreting tears and the passages for drain- ing them off. The gland, 9, is lodged in a depression Fig. III. Chinese Lady. (Whalley.) 28 EYESIGHT, AND HOW TO CARE FOR IT. in the roof of the orbit above and to the outer side of the eyeball, and its secretion is poured upon the ball through a number of small ducts, 10, which open through the free fold of the conjunctiva. Fig. IV. — Lachrymal Apparatus. (The skin of the lids has been removed.) i and 2. Cartilages of lids. 3. Lachrymal canals. 4. Lachrymal sac. 5. Lachrymal puncta, or entrance to canals. 7. Lachrymal lake. 8. Nasal duct. 9. Lachrymal gland. 10. Lachrymal ducts. {Gray?) After passing over the surface of the eye, the tears are taken up by passages, which commence near its inner angle, 3, and conducted into the nose. THE ANATOMY OF THE EYE. On the margin of each lid at the inner angle may be noticed a slight elevation, called the papilla, and on its summit a pinhole opening, called the punctum. Fig. V.—External Muscles of the Eyeball, i. Piece of orbital bone. 2. External straight muscle, with piece cut out. 3. Optic nerve. 4. Internal straight muscle. 5. Upper straight muscle. 6. Lower straight muscle. 7. Upper oblique muscle, attached to ball at 8. 9. Lower oblique muscle. 10. Sclerotic. 11. Cornea. 12. Pulley for tendon of upper oblique. {Gray.) These openings are the mouths of the lachrymal canals, two small tubes which pass nearly horizontally towards the nose and empty into the nasal duct, 8. The ordinary flow of tears is thus drained into the nostril, and they overflow the lids only when the gland is excited to excessive secretion by local irrita- tion of the eye or by mental emotion. A slightly increased secretion may still be carried into the nos- tril and excite the "sniffing" which is usually the first stage of a "good cry." Infants do not shed 3* 30 EYESIGHT, AND HOW TO CARE FOR IT. tears before the third or fourth month, and the ele- phant is the only one of the lower animals accused of this human weakness. The eyeball is moved in various directions by six muscles, (Fig. V.) The straight muscles turn it up- wards, downwards, inwards, or outwards, and the oblique muscles rotate it. The straight muscles, act- ing together, tend to draw it backwards, while the oblique muscles are so placed as to oppose this ten- dency, and the globe is nicely balanced by the proper action of all of them. When, from any cause, one or more muscles act in excess of their opponents, a squint is produced. The operation for squint, or "cross eye," consists in weakening the overacting muscle by cutting it. CHAPTER III. THE PHYSIOLOGY OF VISION. THE act of seeing was involved in the mystery with which all vital functions were in former times invested, until the great astronomer, Kepler, first recognized the fact that the eye is a camera, and, as such, is subject to the same physical laws as any other optical instrument. Images of external objects are formed by the eye exactly as they are formed by a photographer's apparatus ; in the latter they fall upon a chemically sensitive plate, and are made per- manent by the chemical changes induced by light; in the eye they fall upon the nervously sensitive ret- ina, and their impression is conveyed to the brain by the fibres of the optic nerve. To understand anything of the physiology of vi- sion, it is necessary to have a general idea of the way in which images of objects are formed by refracting surfaces. Light emitted from luminous bodies, or reflected from the surface of non-luminous bodies, moves in straight lines, and the smallest conceivable line of light is called a ray. Rays of light," then, are 3» 32 EYESIGHT, AND HOW TO CARE FOR IT. merely suppositious lines used by optici'ans to enable them to bring the effects of an intangible force within the range of mathematical calculations, and to study its exact and unalterable laws. A ray of light is always a straight line while it re- mains in the same medium, or passes through another medium of the same density; but when it passes to a medium of different density, as from air to water or glass, its direction is at once changed. This is well illustrated by a simple experiment with which most people have amused themselves in childhood. Put a small coin in the bottom of an empty vessel, and place the eye in such a position that the coin is just concealed by the edge of the vessel; then let tome Fig. VI. — Refraction at Surface of Water Shown by " Coin Experiment." one pour water into the vessel, and the coin will come into view. The rays of light coming from the coin, as they pass from the denser medium of water to the rarer medium of air, are bent, or refracted, at the THE PHYSIOLOGY OF VISION. surface of the former, and take such a direction that it is possible for them to reach the eye. The object is seen in the direction in which the light reaches the eye, and the coin, situated at a, will appear to be at b (Fig. VI.). Refraction of light is the change of di- rection which its rays undergo in passing from one nfedium through another of different density. The new direction of a refracted ray is determined by the density of the new medium and the form of its surface. A number of parallel rays, or beam of light, passing from the air through a piece of glass with parallel sides, have their general direc- tion displaced, but emerge still parallel on the other side (Fig. VII.). If the surfaces of the glass are curved, and not parallel, the rays are either diverged or converged (Fig. VIII.). If, as in the case of the camera or the eye, the refract- ing surfaces are convex, the rays are brought together on the opposite side at a point called the focus. The focus of a common "burning-glass," in direct sun- light, is simply a minute image of the sun. A bundle of divergent rays, or pencil of light, pro- ceeds from every point on the surface of a visible C 34 EYESIGHT, AND HOW TO CARE FOR IT. object, and each one of these pencils may be brought to a focus by a convex lens. The combination of the Fig. VIII. focii of all the points on the surface of the object will optically re- produce the object, or form an image of it. Thus (in Fig. IX.) the pencil of rays proceeding Fig. IX.— Formation of Image by ° Convex Lens. t0 a focus at x'> those proceeding from b at y, and those proceeding from every point between a and b at a corresponding point between x and y. In this way the picture is formed in a cam- era, which, in its simplest form, consists of a box with its inner surface blackened, a hole in the front in which a convex lens is placed, and a white surface on the back to receive the image that the lens forms of an object towards which it may be directed. In the eye, the sides of the box are represented by the THE PHYSIOLOGY OF VISION. 35 sclerotic, the blackened inner surface by the pigment of the choroid, the opening by the pupil, the convex Fig. X.— Formation of Image on Retina. ( Whalley.) lens by the cornea and crystalline, and the surface to receive the image by the retina. Fig. X. illustrates the formation of an image by this living camera. Thus far the act of vision is a strictly physical proc- ess ; the rays of light can be traced to the image on the retina as definitely and accurately as they can be followed to the screen of the magic-lantern or the plate of the photographer's camera. But beyond this point we find ourselves in the misty region of theory and speculation, and the something that enables the image to excite a sensation, and converts the sensa- tion into a mental process — that evolves thought and reason — like an ignis fatuus, eludes the grasp of science. Prof. Tyndall says that science not only does not explain it, but does not even tend to explain it, and that " when we endeavor to pass from the phe- nomena of physics to those of thought, we meet a 36 EYESIGHT, AND HOW TO CARE FOR IT. problem which transcends any conceivable expression of the powers we now possess. We may think of the subject again and again — it eludes all intellectual presentation — we stand, at length, face to face with the incomprehensible.'' It will be seen by the figure that the image formed on the retina is inverted — upside down; and there has been much learned discussion as to the manner in which we receive from it the impression of an erect object. It must be remembered that, after all, it is the brain that sees, and that it sees not, strictly speak- ing, the external object, but what is called the "pro- jection outward " of its image on the retina, just as we see the picture of the magic-lantern slide projected on the wall. Under favorable conditions, this pro- jected image corresponds in position to the object itself, but those conditions are easily disturbed, when it becomes plain enough that we do not really see the object itself, but only, as it were, a phantom repre- sentation of it. If we look at an object through a prism, the rays of light coming from it are deflected, and, as the image is projected along the last direction of the rays, we see the object in a place where we know it is not, while the position actually occupied by it is blank. The sportsman who wishes to shoot a fish at the bottom of a pond does not aim at the phantom fish, but at the point where he knows the real fish must be. (See Fig. VI.) As the rays of light THE PHYSIOLOGY OF VISION. 17 are crossed in the eye, the inverted retinal picture is projected erect just as the inverted magic-lantern pic- ture is, and for the same reason. Vision is possible even without a retinal image, for an excited or disordered brain may project some phan- tasm of its own conjuring,— some "dagger of the mind,"—and see it as distinctly as if it were a tangible object; hence there have been many honest witnesses to impossible occurrences, whose falsehoods have been, not moral, but purely physiological. All parts of the retina are not equally sensitive to visual impressions. The most sensitive portion is a small space directly in the line of vision, called the yellow spot from a yellow tinge seen in it after death. Indeed, this is the only portion of the retina that ad- mits of distinct vision, and vision becomes gradually more and more obscure from this point towards the circumference. When we look at a large object or a landscape, we see only a small portion of it at a time distinctly, and " the image that we receive by the eye is like a picture, minutely finished in the centre, but only roughly sketched in at the borders." In reading, it is necessary to move the eyes backward and forward along the lines of the print, for without this movement we can distinguish not more than one long word. When we look at an object, we place the eye in such a position in reference to it that its image falls upon the yellow spot, and to obtain an accurate 4 38 EYESIGHT, AND HOW TO CARE FOR IT. idea of our surroundings, the eyes must be in con- tinuous, though unconscious, motion. This necessity for frequent shifting of the line of vision has much to do with the expression of the face. A person of sprightly temperament and active mind wishes to " take in " all that is going on about him, and moves his eyes quickly from object to object to bring them all in rapid succession in the range of his yellow spot; while dull or phlegmatic people are satisfied with a general view of things, and do not take the trouble to focus them all in succession sharply on the most sensi- tive part of the retina. It is a curious fact, that one spot on the retina, not very far from the most sensitive portion, is entirely insensitive to light, and, what at first sight may appear still more curious, this blind spot is at the entrance of the optic nerve, where the nerve fibres are most numerous, and where it might be thought that vision would be most acute. But the nerve fibres belong to the conducting layer of the retina, and the percipient layer, or Jacob's membrane, is, of course, wanting at the point where these fibres pass through it. The existence of this blind spot is very easily demonstrated by means of Fig. XI. Close the left eye, and direct the right to the small cross on the left hand side of the figure. Hold the page vertically before the eye, ten or twelve inches off, and then gradually bring it nearer, still keeping the gaze fixed THE PHYSIOLOGY OF VISION. 39 upon the cross: the round spot will also be visible, except at a certain distance from the eye, about seven Fig. XI. inches, when its image falls upon the entrance of the optic nerve, and it disappears from view. This is illustrated in Fig. XII. Fig. XII. — Blind Spot on Retina. In tracing the rays of light to the retinal image, we have, so far, proceeded as if the rays from all objects required the same degree of refraction to focus them accurately on the retina. This is, however, the case only with distant objects, the rays from which come 40 EYESIGHT, AND HOW TO CARE FOR IT. to the eye practically parallel. All rays in Nature, whose course has not been interfered with, are diver- gent, but beyond a distance of fifteen or twenty feet the divergence is so slight as to be inappreciable, and they are considered as parallel. When the object is brought nearer to the eye, the rays from it are then practically divergent, and require to be more strongly refracted to bring them to a focus. (Fig. XIII.) This Fig. XIII. — i. Focus of Parallel Rays. 2. Focus ot Diver. gent Rays. 3. Focus of Divergent Rays brought forward by more Convex Lens. is a familiar fact in the use of any optical instrument, as an opera-glass; when directed from a distant to a near object, its focus must be adapted to the divergent rays by a mechanism provided for the purpose. It is easy to prove that the eye forms no exception to this rule. If we hold a veil between our eyes and THE PHYSIOLOGY OF VISION. 41 a book, we can either read through it or see its meshes distinctly, but we cannot do both at the same time. While we read, the veil resolves itself into a kind of vague mist, and when we look 'sharply at the veil the print is no longer legible, but blurred and confused. When a fly is seen distinctly on a window- pane, the landscape beyond is obscure; and when the landscape is sharply defined, the fly becomes a shape- less spot. Such experiences show clearly enough that some change takes place in the eye to adapt it to different distances, and, indeed, Kepler, long ago demonstrated that this was a mathematical necessity. Few physiological or mathematical problems have excited more interest or enlisted more talent than the determination of the nature of this change and the means by which it is accomplished. It is now known that the increased refraction by which the divergent rays from near objects are accurately focused on the retina is the result of an increase in the convexity of the lens. When we look at a near object the lens is rendered more convex by the action of the ciliary muscle — a small muscle in the interior of the eye, situated beyond the margin of the lens and con- nected with the delicate ligament that holds it in position. (Figs. I. and II.) Every act of near vision, therefore, is accompanied by muscular effort. The ciliary muscle does for the eye what the adjusting screw does for the opera-glass. The dotted lines in 4* 42 EYESIGHT, AND HOW TO CARE FOR IT. Fig. XIV. show the increased curve in the lens in ad- justment for near objects, and its effect in focusing the divergent rays. This faculty of adapting itself to various distances is called the accommodation of the eye, and is brought into requisition whenever there is the slightest change in the distance of any near object that we look at. Fig. XIV. — Focus of Divergent Rays brought forward to Retina by increased Convexity of Lens. The simultaneous use of both eyes is called " bi- nocular vision," and to secure its correct and full effect, the eyes must have nearly the same acuteness of vision and degree of refraction, and the action of the external muscles must be so balanced that both eyes may be properly directed to the same object. There are, of course, two images formed of every object that we look at, one on each retina, and they are so combined by the brain as to give the impres- sion of one object only when they fall on what are called "corresponding parts" of the two retinae. Taking the yellow spot for the central point, the THE PHYSIOLOGY OF VISION. 43 corresponding portions are those above in each eye or below in each, or on the inner side of one retina and the outer side of the other — that is the por- tions that would come in apposition if one retina were placed upon the other. The most perfect binoc- ular vision is when both images are on the yellow spots, but there is nof double vision unless the images fall on other than corresponding parts, when they are immediately perceived separately, and two objects appear. This is easily shown by pressing one eye slightly out of position with the finger, when everything will be seen double. Or hold two pencils in a direct line before the eyes, six or eight inches apart, and fix the eyes on the nearer one; the other will appear double because its image falls upon portions of the two retinae that do not correspond. The principal advantages of binocular vision are in the appreciation of the solidity (the " three dimen- sions") of objects, and in the accurate determination of distances. When we look at a solid object (with both eyes), the images formed on the two retinae are not precisely alike ; that in the right eye includes more of the right side of the object, and that in the left eye of the left side, and the combination of these two images gives the "stereoscopic effect," or im- pression of relief. This effect is imitated by the ster- eoscope, in which we have two slightly different pic- 44 EYESIGHT, AND HOW TO CARE FOR IT. tures of an object, one taken from the right side and the other from the left, and are enabled to combine them by means of prisms. The effect is even exag- gerated by making the distance between the cameras, when the photographs are taken, greater than that be- tween the eyes, which makes the difference between the pictures more decided. We are greatly assisted in the estimation of dis- tances by the simultaneous use of both eyes, for each eye gives accurately the direction of the object, and we know that its position must be at the intersection of these lines of direction. Persons who have lost one eye are much inconvenienced by the want of this assistance, as may be appreciated by attempting to thread a needle, or to touch a spot on paper with the point of a pencil quickly, with one eye closed. In looking at an object closely, the eyes are turned towards it, or converged, by the action of the internal straight muscles — another muscular effort involved in near vision, which is far from being the merely passive sensation that it is too often considered. The correct interpretation of the impressions re- ceived by sight is after all, to a great extent, a matter of practice and education, with the assistance of the sense of touch. This is proved by numerous obser- vations made upon persons who have been born blind, and whose sight has been restored, or rather acquired, by surgical operation. None of these persons have THE PHYSIOLOGY OF VISION. 45 shown any indication of an instinctive use of their new-found sense; all have had to learn to see. None could distinguish form or distance, or could recognize at first, by sight alone, even objects that had been fa- miliar to touch for years. Some seemed to find their first experiences painful rather than pleasant; and it is related of one, who had earned his living as a street musician and had gone about the town alone for years, that he became confused and lost himself when his eyes were opened, and had to beg some one to lead him home. All this is well illustrated in the inter- esting and instructive, even if somewhat apocryphal, story of Caspar Hauser, who was imprisoned in a dark cell for the first sixteen years of his life. CHAPTER IV. THE OPHTHALMOSCOPE. WHY does the pupil appear black .?" may seem like a very simple question, but thereby hangs the story of one of the most important discoveries of the 19th century. In the beginning of the last century, a French physiologist, while holding a cat under water in the performance of some experiment, was surprised by seeing the blood-vessels of the retina. As the aqueous humor behind the cornea is nearly pure water, its refraction was neutralized by the flat surface of the water in front of the cornea, and this caused the rays of light reflected from the bottom of the cat's eye to pass out of the pupil divergently, and thus rendered visible the structures from which they proceeded. Though not understood at the time, this incident proved that the interior of the eye was not necessarily, under all conditions, invisible, and gave the first hint of brilliant possibilities, whose promise future develop- ments more than fulfilled. The possibility of so mod- ifying the optical conditions as to render the interior 46 THE OPHTHALMOSCOPE. 47 of the eye visible, having once been demonstrated, the problem enlisted many distinguished scientists in its elucidation, and their efforts culminated in the invention of the Ophthalmoscope by Helmholtz, in 1851. When we speak of seeing anything, we mean that rays of light proceeding from it reach our retina, and the pupil ordinarily appears black, because the eye of the observer is not placed in a position to receive the rays of light coming from the interior of the observed eye. If, for instance, we hold a candle in front of an eye to illuminate the pupil, the light thrown back from the bottom of the eye through the pupil, and towards us, will be intercepted by the flame; and, of course, we cannot place our own eye in the course of the rays, between the flame and the observed eye, without shutting off the light altogether. In either case, the pupil of the eye examined will appear black, simply because no light passing out through it can reach our retina. This part of> the problem is solved by using, instead of the candle, a small mirror, usually concave, with a hole in the centre. Light is thrown by the mirror through the pupil, and the observer, by placing his own eye behind the central opening, has it directly in the line of the rays reflected from the interior of the eye examined, a bright red reflection from the blood in the vessels of the choroid immedi- ately takes the place of the usual blackness of the pupil. 48 EYESIGHT, AND HOW TO CARE FOR IT. Having managed to light up the interior of the eye, and to perceive the light reflected from it out through the pupil, it only remains to focus this light accurately on our own retina in order to see distinctly every object from which it comes. This is accom- plished by means of small lenses, of different focal distances, placed immediately behind the opening in the mirror. This forms, substantially, the ophthal- moscope now in general use, which gives a distinct and magnified view of the interior of the eye, and reveals to actual inspection many diseased conditions which were formerly the subjects of theoretical spec- ulations. The lenses also afford the means of meas- uring the focus of the eye examined. The uses of the ophthalmoscope are not confined to ophthalmic surgery, but physiologists have availed themselves of its aid to study the circulation in the only blood-vessels in which it can be seen during life, and general diseases are often detected by the changes that they make in the appearance of the retina and optic nerve. This is particularly true of diseases of the brain, for the ophthalmoscope enables us to in- spect a large nerve within a short distance of its origin in the brain, and one that is wrapped in membranes and contains blood-vessels derived directly from those of the brain itself. CHAPTER V. INJURIES AND DISEASES OF THE EYE. ONLY a brief reference will be made to some of the more common injuries and diseases of the eye, with a view to exposing their dangers and some popular errors in reference to them. The guards with which the eye is provided to pro- tect it from injury, have already been referred to, but, complete as they are, it 'is a matter of wonder that this extremely delicate organ, exposed as it is in numberless ways in its owner's constant pursuit of labor or pleasure, escapes so generally as it does. The most common form of injury is from particles of dust and small foreign bodies. As the course of the tears is from the gland at the upper and outer part of the ball towards the canals at its inner side, (Fig. IV.,) and as the lids are firmly attached to bone at their inner extremities, and only loosely to the soft tissues at their outer, such particles are usually washed by the flow of tears, and moved along by the action of the lids towards the space at the inner angle of the eye, which is called the " lacus lachrymalis," or tear 5 D 49 50 EYESIGHT, AND HOW TO CARE FOR IT. lake. From this we remove them, almost uncon- sciously, with the end of the finger, or perhaps the handkerchief. This little operation is performed very frequently of a wirfdy day. Occasionally, a cinder or piece of coal, or some other object with projecting points, becomes lodged on the conjunctiva, and, as everybody knows from experience, is the cause of most acute pain. A smooth object rarely gives much pain, and is almost invariably passed on by the tears and the action of the lids. This process may be assisted by gentle rubbing of the lids, which, however, only makes matters worse when the offending mote has once taken hold. This com- parative harmlessness of a smooth body has suggested the popular notion of sending it after a lodged one, in the hope that it may displace it and send it on its way, which, it cannot be denied, is occasionally ac- complished. Druggists sell, for this purpose, what are called eye-stones, which are supposed by some to have a mysterious kind of semi-intelligent action which enables them to search out and capture the in- truder. The genuine article is the operculum, or lid, of a small shell found on the sea-shore; but when the stock of these is exhausted, some smooth seed, as a small bean or flaxseed, is sometimes substituted. A patient recently presented herself at the eye hospital with a highly inflamed and very painful eye, with which she had been suffering for weeks. When the INJURIES AND DISEASES OF THE EYE. 5 I lid was everted, a germinating seed with quite a well developed sprout was found in the fold of the con- junctiva, where it had been liberally supplied with the requisites of warmth and moisture. The patient then remembered that she had placed her faith in an " eye-stone." It is hardly necessary to warn intelligent readers against such mistakes as this, but it may be well to suggest that it is a very simple and easy thing to evert the eyelid, and that many hours of really serious suf- fering may often be saved by it, particularly in travel- ling. Direct the sufferer to look well downwards, then, taking the lashes of the upper lid between the finger and thumb, stretch the lid downwards and out- wards, place the point of a pencil on the upper part of the lid, above the top of the ball, and press it downwards while the edge of the lid is raised. The inner surface of the lid is thus exposed, and the cinder can be readily removed by touching it with a fold of a handkerchief. When the mote is just within the margin of the lid, it may sometimes be removed by drawing the upper lid well down and pressing it against the skin of the lower lid. When the foreign body has lodged on the firmer tissue of the cornea, its extraction is not so simple a matter, and rubbing only presses it in more firmly. The particle is usually driven with some force, as from a hammer or turning-lathe, but may be simply 52 EYESIGHT, AND HOW TO CARE FOR IT. blown into the eye, and imbedded in the cornea by pressing the lid against it. Often a minute piece of iron, that can scarcely be seen without a magnifying- glass, will give rise to great pain and intense inflam- mation. If it is completely imbedded, so as not to present any sharp point to scratch the lid in its move- ment over the cornea, the pain will be comparatively slight, but the resulting inflammation may still be severe. A foreign body should always be suspected, if a violent inflammation is lighted up suddenly with- out apparent cause, particularly if one eye only is affected. Of course, the only remedy is the removal of the offending particle, which should be accom- plished without delay, but should not be intrusted to unskilful hands. Specks of iron and steel, however, may often be removed safely and promptly by the use of a strong magnet, which would be a useful thing to have at hand in establishments where work- men are liable to such accidents. Wounds made with pointed instruments, such as scissors or fork, frequently penetrate the cornea and injure the lens, when a cataract is formed. This, in young people, is usually absorbed, but in adults may require an operation for its removal. A not uncommon and a dangerous form of injury is that from lime splashed into the eye. Quick-lime acts as a powerful caustic, and often causes complete blindness by destroying the vitality of the cornea. INJURIES AND DISEASES OF THE EYE. 53 Even when the conjunctiva only is affected, the eye may be seriously disabled by a growing together of the raw surfaces of the lid and ball. The lime should, of course, be instantly washed out, as thor- oughly as possible, with water, and any that may remain should be neutralized by bathing with a tea- spoonful of vinegar in a glass of water, or rendered inert by sweet-oil. The latter is equally efficient and more soothing. In case of injury by- acids, one part of lime-water to three of water may be used, or the eye may be freely bathed in milk. Sympathetic Ophthalmia.—When the eye is exten- sively lacerated by a wound, or when a foreign body is lodged in the ball, the effect is not always confined to the injured eye, but there is great danger of the other being lost by sympathetic inflammation. In nearly all such cases, the only safety from ultimate blindness is in the removal of the offending eye, which is no longer either useful or ornamental, but has become merely a dangerous de- formity, and sooner or later, some- times after many years, is pretty sure to give trouble. Fortunately, Fig. XV. the operation for the removal of Artificial Eye. a disorganized eye is not a serious one, and the result- ing disfigurement can, to a great extent, be concealed by the use of an artificial eye. 5* 54 EYESIGHT, AND HOW TO CARE FOR IT. Such perfection has been reached in the manufac- ture of artificial eyes, that close examination is often needed to distinguish them from the natural organ. They are thin shells, the edges of which fit into the folds of the conjunctiva, and they are held in place by the lids. One should never be worn more than two or three years, as, when the enamel is eroded by the tears and mucus, it loses the perfect smoothness of its surface and becomes a source of irritation. Catarrhal Ophthalmia. — The most common dis- ease of the eye is inflammation of the conjunctiva. Its simplest form is the catarrhal, in which the mucous membrane of the eye is affected in the same way as that of the throat and nose, and often at the same time. As the membrane is continuous with that of the nose and throat, its diseases may be so too, as in the case of influenza. It usually yields readily to rest and simple treatment, but if not checked, may run into the purulent form, or may become chronic and end in the condition known as granular lids. This latter is a very tedious and obstinate complaint, and is well known and much dreaded by patients who frequent hospitals and dispensaries. The inner surface of the lids becomes thickened and rough like sand-paper, and, by constant friction, impairs the transparency of the cornea. When the discharge in catarrhal ophthalmia consists only of an excessive secretion of tears and mucus, it is probably not con- tagious, but if pus is mingled with it, it may become INJURIES AND DISEASES OF THE EYE. 55 so at once, and in all cases it is prudent to take pre- cautions against communicating the disease by allow- ing the smallest particle of the matter to come in contact with a healthy eye. It often prevails in an epidemic form in the spring, when frequent and ex- treme changes in temperature and prolonged damp- ness predispose to affections of the mucous membranes, and the eyes are irritated by wind and dust. Purulent Ophthalmia differs from the preceding form principally in degree, and it is sometimes difficult to draw the line where one ends and the other begins. The discharge, which is thick and yellowish, and, in bad cases, very copious, is undoubtedly and viru- lently contagious. Whole families are sometimes inoculated by the discharge from the eyes of an in- fant who has had the disease so slightly as scarcely to attract attention. It is not common among adults who live in clean and roomy homes with comfortable surroundings, but is met with often enough in very young infants to be considered one of their special diseases. It is most frequent where a number of people are crowded together* as in barracks, asylums, charity-schools, etc. Some of the most frightful epi- demics formerly occurred on slave-ships. It is sometimes called Egyptian ophthalmia, from its great frequency in Egypt, where it prevails to such an extent as to assume the proportions of a national scourge, and the number and wretchedness of its vie- 56 EYESIGHT, AND HOW TO CARE FOR IT. tims sadden the journey of sympathetic travellers. Its causes are exposure to intense heat and glare, the high winds driving clouds of sand before them, and the poverty and ignorance of a large portion of the inhabitants. Many soldiers of the Crusades were victims of this disease, and numbers of blind beggars groped about the streets of London and Paris, appealing to the sympathies of the passers-by with the cry of " Holy Land ! " " Holy Land ! " to show that they had lost their sight in the popular cause. . Three hun- dred of these persons were cared for in an asylum established in Paris by Louis IX., which, from the number of its inmates, was called " Les Quinze Vingts." It is still in existence, with the same name, and is the oldest institution for the blind in the world. Purulent ophthalmia is one of the most dangerous diseases to which the eye is subject, and its victims are the most numerous in asylums for the blind. Fortunately, in a large proportion of cases, it yields to proper treatment, particularly the form occurring in infants, which is nearly always curable in its earli- est stages; but no time should be. lost, as, in a bad case, a few hours sometimes decide the patient's fate. The most scrupulous cleanliness is always essential, and the greatest care must be taken that no towel or basin that the patient uses shall be used by any one else. When the disease appears in a building where INJURIES AND DISEASES OF THE EYE. 57 a number of persons are congregated, every one at- tacked should be immediately isolated, at whatever inconvenience. The conjunctiva is nearly always inflamed in mea- sles, and frequently in scarlet-fever and small-pox, and occasionally the diphtheretic membrane is formed upon it, either with or without an accompanying af- fection of the throat. There is danger in such cases that, in the overshadowing anxiety for the patient's life, the eyes may not receive due care and attention ; but it should always be remembered how little of the pleasure and usefulness of life is saved if sight is lost. The question is frequently asked whether it is bet- ter to bathe the eyes in cold or warm water. So far as external bathing is concerned, this is merely a question of comfort that may be decided by the ex- perience of the individual; but it is not well to apply anything to the conjunctiva unless it is inflamed. Many people have an idea that it strengthens the eyes to open them under water, but, as we are not amphibious animals, though the eye may be able to bear this exposure to an unnatural element, it cer- tainly cannot suffer for the want of it. Healthy eyes, if given anything like a fair chance, will take care of themselves, and need no attention beyond what may be necessary to avoid abusing them. Diseases of the cornea may destroy or impair its transparency, or the ulcers that are frequently formed 58 EYESIGHT, AND HOW TO CARE FOR IT. may extend through its substance, allow the aqueous humor to escape, and involve the iris. Even when such ulcers heal most favorably, they, leave a perma- nent scar in the form of a white speck. Inflamma- tion of the cornea is usually painful and accompanied with distressing sensitiveness to light. It occurs most frequently in persons whose health has been subjected to some depressing cause, or in children who have in- herited a delicate constitution. Many of the latter are subject to repeated attacks for years, but the ten- dency to their recurrence generally disappears before adult life, and if care be taken to prevent each attack from leaving a permanent mark, the eyes may finally remain sound and strong. A large, white opacity of the cornea is often mis- taken for cataract, and not many years ago, when a knowledge of diseases of the eye was not so general as now, this mistake was sometimes made by physi- cians, and such patients were sent hundreds of miles to have the cataract removed. Iritis, or inflammation of the iris, often destroys sight by closing the pupil and shutting off the light from the interior of the eye. This very rarely hap- pens if the disease is promptly and skilfully treated, but it is often masked by an accompanying inflamma- tion of the conjunctiva; the patient, perhaps, thinks " it is only a cold," and neglects it until the mischief is done. It should always be suspected when, in an acute INJURIES AND DISEASES OF THE EYE. 59 affection of the eye, the sight is decidedly diminished and there is some pain in the ball, and particularly in the brow. The latter is always more severe at night. Cataract is a disease of the crystalline lens. The lens becomes opaque, and obstructs the entrance of light so completely that, when the cataract is fully formed, the patient can merely distinguish light from darkness. The pupil loses its natural blackness and the whitish surface of the opaque lens is seen just be- hind it. Cataract is not "on the eye," as is popu- larly supposed, but in it. The mistake arises from confounding cataract with the whitish opacities of the cornea already referred to. Treatment by any kind of medication is entirely useless; the only remedy is the removal of the lens by operation. Of course, in the absence of the lens, the light cannot be focused accurately upon the ret- ina, and people who have undergone this operation have no distinct vision until a convex lens of glass is placed in front of the eye. As no artificial lens can imitate the power of the crystalline to accommodate its focus to different distances, two glasses are re- quired, one for distance and one for reading. Glaucoma is a disease in which an excess of the fluids of the eye makes the ball tense and hard, and exerts injurious pressure upon its delicate contents. In acute cases it is intensely painful, and rapidly destroys sight by pressure upon the nerve. In its earliest 60 EYESIGHT, AND HOW TO CARE FOR IT. stage, its progress can nearly always be checked by an operation which consists in cutting out a piece of the iris; but when the nerve is once paralyzed, the case is hopeless. In no disease are early recognition and treatment more important, and many of its victims have been condemned to blindness by delay. No one with a violent pain in the eye and head, particularly if it is accompanied by flashes of light, rainbow colors, or dimness of virion, should allow himself to be lulled into a sense of security by calling it " neuralgia." Diseases of the choroid and retina can be recognized only by the ophthalmoscope. When uncomplicated, they are painless, and may give rise to no other symp- toms than dimness of vision — a symptom that, in all cases, is entitled to respectful consideration. Amaurosis.— Before the invention of the ophthal- moscope enabled us to examine the interior of the eye, a number of unseen diseases were classified to- gether under the general term of amaurosis, which was humorously, but not inaptly, described as a "dis- ease in which the patient sees nothing and the physi- cian sees nothing." Now, this vague term is rarely used, and only to indicate paralysis of the optic nerve or blindness resulting from disease of the brain. Tobacco amaurosis is a form of partial paralysis of the optic nerve met with in excessive smokers. Ex- cessive use of alcoholic drinks is thought, by some authorities, to induce the same condition. INJURIES AND DISEASES OF THE EYE. 61 There is a popular notion that floating specks be- fore the eye, or muscce volitantes, are a symptom of "amaurosis," and they consequently very often oc- casion much unnecessary uneasiness, particularly to persons of nervous temperament. They have the form of small spots or circles, strings of beads, or gossimer threads, and float about in the field of vision. They are the shadows cast upon the retina by microscopic opacities in the vitreous humor, wlv'ch do not usually attract attention, and are frequently met with in perfectly healthy eyes. " Muscae " may be made evident in any eye by looking through a small pinhole in a card at a bright light covered by a ground glass globe. The dread excited by these specks, in the minds of people who devote themselves to watching them, sometimes almost amounts to mon- omania. Color-blindness is the inability to distinguish cer- tain colors. Base colors are those by the mingling of which, in proper proportions, we may produce any one of the other colors of the solar spectrum, or white, which is a combination of all of them. Red, yellow, and blue were formerly considered the base colors, but Thomas Young preferred red, green, and violet, and these have also been accepted by Helm- holtz and others. This has reference to the mingling of colors by the retina, and not to the mixing of pigments. According to what is known as the 6 62 EYESIGHT, AND HOW TO CARE FOR IT. Young-Helmholtz theory, there are special retinal elements for each of these base colors,; when all of them are simultaneously and equally excited, the sen- sation of white results, and the different colors are produced by the excitation of one or more of these elements in varying degrees. A person completely color-blind for any one color is deficient in one set of elements, and his percep- tion of other colors is affected just in the proportion that this one enters into their composition. The case may be complicated by partial color-blindness, and it must be confessed that there are many compli- cations which are still subjects of discussion, and which prevent this theory from taking its place among those which may be considered as finally ac- cepted. A greater portion of the retina is naturally color- blind ; in fact, perfect color-vision exists only in the central portion, around the "yellow spot." This may be readily proved by keeping the eye fixed, and passing some small red object, as a wafer, slowly across the field of vision. It will be found that the color fades away long before the form of the object becomes invisible. Green can be recognized beyond the limit for red, and the perception of blue extends beyond that of green. The most common form of color-blindness is that in which red is deficient. It is frequently called INJURIES AND DISEASES OF THE EYE. 63 " Daltonism," because first carefully described by the great English chemist, Dalton, who was himself a subject of it. He was a strict Quaker, and when he was about to be presented at court, it was feared by his friends that it would be impossible to induce him to wear the scarlet robe, in which custom demanded that a doctor of civil law should appear. But it seemed to him like a harmless gray, and, finding it comfortable, he persisted for several days in wearing it about the streets of London, surmounted by a broad-brimmed hat, and with drab pantaloons peep* ing out beneath it. Color-blindness is sometimes produced by disease, but usually exists at birth, and is often hereditary. It will be readily understood that in many occupa- tions it is a serious disability, and, as the subject of it is frequently unconscious of the defect, the eyes should always be tested before such occupations are undertaken. Some otherwise excellent artists have been spoiled by it. It is a matter of grave impor- tance in the case of seamen and of railroad engineers, and has lately attracted much attention in that con- nection all over the world. A green light at night marks the "starboard " or right-hand side of a ves- sel, and a red light the "port" side; while a red light on railroads is the signal for danger. A color- blind pilot or lookout has no means of knowing, on a stormy night, whether a vessel that he must pass is 64 EYESIGHT, AND HOW TO CARE FOR IT. steering to the right hand or to the left; and a loco- motive engineer who cannot distinguish between red and green, does not know the difference between dan- ger and safety to the hundreds of passengers whose lives are in his hands. The Swedish, Russian, and Bavarian governments have ordered all persons con- nected with railroads to be tested for color-blindness; in Italy, all railroad employe's are subjected to rigor- ous examination; and investigations have been, or are being, made on an extensive scale in France, Bel- gium, Holland, Denmark, and Finland. In Finland, of 1200 employes examined, sixty were found color- blind. Not much progress has been made in Eng- land, though Prof. Tyndall has added his warning to that given strongly, twenty years ago, by Wilson; and little or nothing has as yet been done in this country. This defect is much more frequent than is com- monly supposed. Of a large number of men exam- ined in Europe and this country, four or five per cent, have been found color-blind. Women enjoy, comparatively, a singular immunity. Drs. Cohn and Magnus found only one color-blind among 2318 school-girls tested in Breslau, and Dr. Jeffries found only two among nearly 2000 women and girls ex- amined in Boston. No satisfactory explanation has been given of this fact, but it appears to be pretty well established, and, until a careful system of testing has been adopted, ladies who feel aggrieved that their INJURIES AND DISEASES OF THE EYE. 65 sphere of usefulness is too much restricted might well inscribe it on their banners in an advance, by land and sea, on every position where signal-lights are used. As the crystalline lens grows dense with age, par- ticularly if there is commencing cataract, a yellow tinge often takes the place of its natural colorless transparency. This must partially impair the percep- tion of the complementary color, blue, to the extent, at least, of requiring a deeper tinge to produce a given effect. Liebreich, therefore, in his London lecture on Turner and Mulready, took the ground that the excessive blue in the later pictures of Mul- ready, who continued to paint after he was seventy years of age, was due to yellow degeneration of the crystalline lens, and maintained that this excess of blue could be neutralized, and these pictures could be restored to the harmony of the artist's earlier pro- ductions, by looking at them through a glass slightly tinted with yellow. Persons who have been operated upon for cataract sometimes complain, after the yel- lowish lens has been removed, that everything appears to them unnaturally blue. This effect soon passes off as the retina becomes accustomed to white light. Among the causes of defective sight, hereditary transmission of optical defects, or of a tendency to particular forms of disease, is important. It is met with in various forms. Color-blindness, 6* E 66 EYESIGHT, AND HOW TO CARE FOR IT. as has already been observed, is in a high degree hereditary. Prof. Wilson says, " it is a safe estimate, that every decided case of color-blindness implies the existence of another case of equal or similar severity in the person of a relative," and Dr. Pliny Earl, some years ago, gave the history of color-blindness in five generations of his own family. Any anatomical or physiological peculiarity that has existed from birth (that is, "congenital"), is liable to be transmitted to the next generation, and persons blind from such causes would be liable to have blind children. The case is different, however, with acquired blindness, and many instances have been recorded of children with perfect eyes being born to blind parents. Four marriages of blind per- sons are known to the officers of the Pennsylvania Institution for the Blind; there were one or more children in each instance, and all had good sight but one, who was born quite blind, and this was the only case in which the blindness of either parent was con- genital. Six of the inmates of this institution are the children of blind or partially blind parents. The defects in focus, or optical defects, as will be explained in the next chapter, are dependent on the form of the eyeball, and are therefore very liable to be inherited. This is particularly the case with short- sight, the predisposition to which, at least, is consid- ered by the best authorities to be in a large propor- tion of cases hereditary. INJURIES AND DISEASES OF THE EYE. 6j A peculiar affection ("Retinitis Pigmentosa"), which is recognized, with the ophthalmoscope, by the presence of black spots upon the retina, shows a very marked tendency to hereditary transmission. It also sometimes occurs in several members of a family, though its existence in a previous generation cannot be established. The prominent symptoms are "night-blindness" and a gradually increasing contraction of the field of vision. Its subjects may be able to go about alone well enough in daytime, but become helpless after sundown ; and may see accurately with a small central space of the retina and be blind in other parts of it. Some authors set this affection down among the various evils let loose by the Pandora of consanguineous marriage, but, after much discussion, the most that can as yet be said of this view is that it is not proven. The pro- portion of cases that have been observed among the children of near relatives has not been large enough to exclude the possibility of mere coincidence. A tendency to gouty or rheumatic iritis, to certain forms of inflammation of the optic nerve and retina, and to some forms of cataract, may be inherited, but perhaps is not so frequently as might be expected; while there are general diseases whose inherited taint manifests itself in the eyes of children, though the parent from whom it has been derived may have had no affection of the sight. CHAPTER VI. OPTICAL DEFECTS: OLD-SIGHT, LONG-SIGHT, SHORT-SIGHT, ASTIGMATISM. AS the eye is a camera, just as subject to the ordi- nary laws of light as any other optical instru- ment, it may be free from disease and perfectly sound, and vision may still be indistinct because the rays of light are not accurately focused upon the ret- ina. The causes that give rise to such imperfections of sight are called optical defects. Presbyopia, or old-sight, is the most common of these; in fact, unless neutralized by short-sight, it is, of a physical necessity, universal with all of us who live beyond middle age. People of fifty-five or upwards are frequently heard to boast that they can read perfectly well without glasses. Prof. Donders says of them, " such people consider themselves a lucky exception. They are extremely proud of their sharp sight. The inquiry whether they are near- sighted is answered in the negative, with a smile of self-complacency." But when their distant-sight is compared with the natural standard, it is invaria- 68 OPTICAL DEFECTS. 69 bly found to be deficient. The degree of the defect may be slight, and they may be unaware of it, but it necessarily exists. Old people who have been using glasses for twenty or thirty years, are sometimes sur- prised by a return of the ability to read without them, and this is spoken of as "second sight; " they have become short-sighted in consequence of a change that has taken place in the shape of the lens. " Old-sight " is simply a partial loss of the power to accommodate the eye to different distances. A general explanation of this power of accommodation has been given, (Fig. XIV.,) from which it will be seen that the divergent rays of light coming from near objects are brought to a focus on the retina by increasing the convexity of the lens. Of course, this change in the form of the lens will be accomplished more readily in proportion as its substance is soft, and with greater difficulty when it is denser. Now, one of the most constant of the physiological changes that accompany advancing age is an increase in the density of the crystalline lens, and a corresponding diminution in the ability to change its form. Hence, the nearest point of distinct vision, which corre- sponds to the greatest convexity of the lens, year by year recedes from the eye. A child ten years of age can see small objects distinctly at two and a half or three inches from the eye ; at about this time the change becomes manifest, and steadily advances until JO EYESIGHT, AND HOW TO CARE FOR IT. the age is reached when we commence to " trombone our newspaper " in search of the receding near point of distinct vision, which at first becomes doubtful, and finally ceases, practically, to exist. '' Far-sighted'' is not a correct term for this condition ; the far point of distinct vision is not altered, the near point is simply removed so far from the eye that small objects are no longer visible. The first symptom of old-sight is a demand for brighter light and clearer print, and at length, some- where between the ages of forty and fifty, dim light and poor print become so universal that we are forced to admit that our eyes are at fault, and to seek aid of the optician. The proper time to commence using glasses is when it is no longer possible to read with perfect comfort without them. A contest with age is hopeless, and it is the part of wisdom to yield grace- fully to the first summons to surrender. A convex glass is used to supplement the failing power to increase the convexity of the lens, and it is important that a proper glass should be selected. A common mistake of opticians is to commence with too strong a glass. People are apt to be pleased with such glasses, because by magnifying small print they make it unnaturally clear. It is by no means neces- sarily the case, though, that the glass that may seem most pleasant on first trial is the one that will give the most comfort in a long evening's work. The ob- OPTICAL DEFECTS. J\ ject of the glass is not to magnify, this is merely an incidental effect, but to assist the lens in focusing divergent rays of light; only so much assistance as is really needed should be given, and anything more than this may be injurious. There is such a wide range of individual differences in the condition of the eyes, in nervous force, occupations, etc., that the attempt, sometimes made, to adapt glasses arbitrarily according to age is absurdly irrational. The same care should be exercised in increasing the power of the glasses as age advances; it should be done with reference, not to any stated intervals, but to the pro- gressive failure of accommodation. It is well for per- sons who read or write a great deal by clay and night to use the stronger glasses in artificial light only, and the old pair in daytime. Hypermetropia, or long-sight, should not be con- founded with the previous condition, as it very fre- quently is. This mistake is a natural one, as both conditions require convex glasses, and both are popu- larly called " far-sight," though this is not a correct term for either of them. Presbyopia, or " old-sight," as has already been explained, affects merely the near point of distinct vision, which is removed further from the eye ; while in hypermetropia both the near and the far point are involved, and there is no dis- tinct vision at any distance without a strain; this strain exists even for distant vision, but becomes 72 EYESIGHT, AND HOW TO CARE FOR IT. greater the nearer the object looked at. Old-sight is a failure of the power to accommodate the focus of the eye to near objects, resulting from a natural change, in the density of the lens; while hyperme- tropia is a defect in the focus, dependent upon the form of the eye, and exists in childhood. The term " far-sighted " is not a good one, because, though such eyes may see perfectly well at a distance, and much better than near by, they cannot see further than the perfectly formed (or "'emmetropic") eye. The ex- pression long-sight is sometimes used to denote the contrast with short-sight, which is the opposite con- dition in cause as well as in effect; in short-sight, the distance between the cornea and the retina is too great, and in hypermetropia it is not great enough. It will be remembered that the perfectly formed eye, when in a state of rest, is adapted to parallel rays of light, which are therefore brought to a focus accurately upon the retina, where a distinct image of the external object, from which they come, is formed. Such an eye is called emmetropic, from the Greek word emmetros, according to measure, because the measure of its axis, or the distance between the cor- nea and the retina, is the same as that of its focal distance, or the distance between the cornea and the point where parallel rays are brought to a focus. If either the axis of the eyeball or the focal distance of the eye is too long or too short, if they do not ac- OPTICAL DEFECTS. 73 curately correspond, the focus will not fall upon the retina, but in front of it or behind it, and this is what is meant by "an error of refraction." This is easily illustrated by holding a convex lens, or com- mon magnifying-glass, in such a position in front of a piece of white paper that the image of some object, as a candle-flame or window-sash, will be formed upon the paper. When the outlines of the image are sharp and the picture is clear, the distance between the lens and the paper corresponds to the focal distance of the lens, just as in the emmetropic eye the distance between the cornea and the retina corresponds to the focal distance of the refracting surfaces of the eye. If the paper is moved ever so little, towards or away from the lens, the distance is no longer "according to measure," and the image becomes indistinct; pre- cisely in the same way, the retinal image becomes in- distinct if, from an imperfection in the form of the eyeball, the retina is too near or too far from the cornea. In hyperme- Fig. XVI.—Hypermetropia. tropia {hyper- nietros, beyond the measure), the axis of the eyeball is too short, and the focus falls beyond the retina, 7 74 EYESIGHT, AND HOW TO CARE FOR IT. which is too near the cornea. If the shape of an emmetropic eye be compared to that of an orange, a hypermetropic eye will have more the form of a tur- nip. In Fig. XVI., the continuous outline shows the form of the emmetropic eye, and the dotted curve indi- cates the position of the retina in hypermetropia. It will be seen that rays of light which enter the eye par- allel are intercepted by the retina, in this false posi- tion, before they are brought to a focus, and that only convergent rays can be focused accurately upon it. As all rays of light that have not passed through a convex lens are either divergent or parallel, and con- vergent rays are not met with in Nature, it would seem, at first sight, that an eye with too short an axis could have no distinct vision at any distance. This would be the case if it were not for the power of accommo- dation, which enables the eye, by increasing the con- vexity of its lens, to bring the focus forward on to the retina. (See Figs. XIII and XIV.) This, however, as has been explained, is accomplished by muscu- lar action, and such an eye is subject to constant strain; even distant vision, which in the perfect eye is a passive sensation consistent with entire rest of the organ, requires an effort. In reading, the effort required, even by the natural eye, must be added to that already in use for distance, in the case of the hypermetropic eye, and the strain is propor- tionately increased. OPTICAL DEFECTS. 75 In very young people, in whom the lens is soft and easily acted upon, and who usually occupy themselves less constantly in close work, a very considerable de- gree of hypermetropia may pass unnoticed; but sooner or later, according to the degree of the defect, the vigor of the individual, and the nature of his occupation, the time must come when the strain will manifest itself by discomfort, distress, or complete disability for anything but manual labor. At first there is merely a sense of fatigue on prolonged use of the eyes, with, perhaps, a slight pain or "heavy feeling" in the brow. Then, after reading for a time, particularly at night, the print, which at first may have been perfectly sharp and clear, becomes blurred and misty, or even fades away entirely ; by closing the eyes for a little while, and, perhaps, rub- bing or bathing them, it is possible to resume the strain, but the same experience is repeated. Persons who persist in struggling on in this way have, for some time after the work is laid aside, a feeling of fatigue and discomfort in the eyes, accompanied by headache, and not unfrequently dizziness, irritability, and mental confusion. Finally, in many cases, the tension of the accommodative power required for dis- tant vision is felt, and these symptoms, to a greater or less extent, become continuous, even when no attempt is made to use the eyes for near work. The hopeless condition of such persons, before Donders 76 EYESIGHT, AND HOW TO CARE I-OR IT. explained the true cause of their troubles, and re- duced its treatment to a rational physical basis, may be judged from the following quotation from Macken- zie, the highest authority of the last generation : "In many cases, it is our duty to declare the disease in- curable. If the patient is a young lad, bound ap- prentice to a sedentary trade, and the disease, from its duration and its mode of origin, not likely to yield to treatment, we may advise him to turn shop- keeper, to apply himself to country work, or to go to sea; if a female, occupied constantly in sewing, to engage in household affairs, or any other healthy, active employment. Many a poor man have I told to give up his sedentary trade, and drive a horse and cart; while to those in better circumstances and not far advanced in life, I have recommended emigration, telling them, that though they never could employ their eyes advantageously where much reading or writing was required, they might see sufficiently to follow the pastoral life of an Australian colonist." Now and then a child discovered by chance that he could study his lessons, or read his novel, comfort- ably through his grandmother's spectacles; but his mother snatched them from him as she would a loaded pistol or a cup of poison, and his family physician lectured him solemnly on the terrible risks he was running. The obvious and certain remedy for all these OPTICAL DEFECTS. 77 troubles — obvious enough, now that a master mind has pointed out the way to us — is to use the convex glass (Fig. VIII.) that will give to parallel rays of light the necessary degree of convergence before they enter the eye. The muscle of accommodation is thus re- lieved of its extra work, the focus is brought forward on to the retina, and the focal distance of the eye and the glass together is " according to measure." Short-sight has for many years been called myopia, from two Greek words meaning to close the eye, be- cause short-sighted persons have the habit of half- closing the lids in the effort to see distinctly; and this term has been retained by modern authors. Fig. XVII. —Myopia. While in the perfectly formed or emmetropic eye the focus for parallel rays of light falls accurately upon the retina, and in the hypermetropic eye falls beyond it, in myopia it falls in front of the retina. In hy- permetropia the axis of the eyeball is shorter than the focal distance for parallel rays, and only conver- 78 EYESIGHT, AND HOW TO CARE FOR IT. gent rays can be brought to a focus upon the retina; in myopia the axis is too long, and no object can be » seen distinctly until it is brought near enough to the eye to throw the focus of the rays of light coming from it back to the false position of the retina. In Fig. XVII., the continuous line shows the proper form of the eye, and the dotted line indicates the position of the retina in myopia. It is thought that the tendency, at least, to short- sight exists, in most cases, at birth, and that it is, in a high degree, hereditary. It is possible, however, that it may sometimes originate in later life from abuse of the eyes, and there is no doubt that it is de- cidedly, and often very rapidly, increased. That it is extensively increased by close work, and is trans- mitted from parents to children through generations, is shown by its invariably greater prevalence among the classes that make most demand upon the eyes. It is one of the penalties of advancing civilization, and is met with more frequently in old communities than in new, in cities than in the country, in the pro- fessions and among students and literary people than among those who labor only with their hands. Its greatest prevalence is in Germany, where it has long been impossible to fill the ranks of the army without allowing soldiers to wear glasses. It is comparatively rare among seamen and farmers, and no one ever heard of a short-sighted Indian. OPTICAL DEFECTS. 79 Even with the greatest care, there is nearly always more or less increase of myopia during the period of childhood and youth, when the organs are growing and the tissues are rapidly changing, and the results of imprudence and abuse are so disastrous that this is one of the most important problems that the re- formers of the age have to deal with. The statistics upon this subject are really startling. Dr. Cohn, of Breslau, some twelve years ago, examined the eyes of more than 10,000 school-children, and found the percentage of short-sight increasing, from year to year, as shown by the following table: Elementary school, . . 6.7 per cent. Intermediate school, . 10.3 " High school, . . . 19.7 " Gymnasia, . . . 26.2 " And in the high schools one-half of the first class were found to be short-sighted. Other examinations, since made in Europe and in this country, show the same tendency. Because short-sighted people can see small objects with great distinctness, and may be able to read after middle age without glasses, there is a popular notion that short-sighted eyes are stronger than others. This is a dangerous delusion. Though myopia may remain stationary, and may be merely a matter of slight in- convenience, which is, to a great extent, compen- 80 EYESIGHT, AND HOW TO CARE FOR IT. sated for by the ability to read without glasses at the age when others are entirely dependent upon them, an eye with a high degree of short-sight is almost always an unsound one. The essence of the defect is a bulging backward of the outer coat or sclerotic, which yields more readily as it becomes stretched and thin; and any excessive strain of the eye, anything that causes an increased flow of blood to the interior of the eyeball, adds to the pressure upon this weakened membrane, and forces it further back. The delicate choroid and retina, in attempting to follow the distended sclerotic, are seri- ously injured by the stretching. When the disten- sion is very rapid and excessive, the retina sometimes becomes detached, and lies in loose folds in the disor- ganized vitreous humor, and there is an end to sight. This result may be considered exceptional, but it is not very infrequently met with, and should be borne in mind as a possible, though usually avoidable, ter- mination of any case of rapidly progressive myopia. Inflammation of the choroid is also common in ex- cessively short-sighted eyes, and large white spots, the result of wasting of this membrane, are frequently seen by the ophthalmoscope. In short, myopia, when it exists in a high degree, is, in a large proportion of cases, a serious disease, which requires the most careful and skilful treatment. Another common mistake is the belief that short- OPTICAL DEFECTS. 8l sight diminishes with age. It will be remembered that old-sight affects only the near point of distinct vision, and not the far point; hence its effect upon a short-sighted eye will be to prevent it from seeing small objects so near as in youth, but not to make distant vision more distinct. As a short-sighted eye is adapted only to divergent rays of light, it requires, for distant vision, the con- cave glass (Fig. VIII.), that will give to parallel rays the necessary degree of divergence. If, for instance, the farthest point of distinct vision is twelve inches, dis- tant objects will be made distinct by a double concave glass of twelve inches focal distance; because such a glass gives to parallel rays of light coming from a dis- tance the same degree of divergence that light has which comes from an object twelve inches from the eye. Persons beyond middle age, and sometimes younger persons, who are too short-sighted to read comfortably without glasses, require two pairs, one for distance and one for reading. The selection of glasses for short-sight requires great care, as much harm may be done by using those that are too strong or that are not properly fitted to the eye. In many cases, the plan of " trying " the various glasses on the optician's counter — or, far worse, the peddler's box — is about as rational and safe as it would be, in case of sickness, to try the contents of the various bottles on the drug- gist's shelf without a prescription. F 82 EYESIGHT, AND HOW TO CARE FOR IT. As long-sight and short-sight depend upon the length of the axis of the eyeball, and not upon the curve of the cornea, it is hardly necessary to denounce the absurd pretensions of quacks, who have professed to cure them by increasing the convexity of the cor- nea with a suction apparatus, or diminishing it by pressure. Astigmatism is an optical condition of the eye in which, from a want of uniformity in the curvature of the cornea, different meridians have a different focus. The perfectly formed cornea is part of a sphere or globe, and has the same degree of convexity in all directions, and therefore the same focal distance for all meridians. The astigmatic cornea is not symmet- rical, but has different curvatures in directions at right angles to each other. Rays of light passing through the greatest curvature have the shortest focal distance, and those passing through the least curvature have the longest focal distance; and no sharply defined image can be formed by such a cornea. As a rough illus- tration, draw a line around an egg through the ends, and another around the middle, at right angles to the first; it will be evident that these lines have a very different curvature, and that if the egg were made of glass it could not form a sharp focus, as a glass sphere does — it would be astigmatic. Thus an astigmatic eye may be able to focus sharply either perpendicular or horizontal lines, but it cannot focus them both at OPTICAL DEFECTS. 83 the same time, or with the same accommodative effort at a given distance. One meridian may be correct and the other myopic or hypermetropic, which is simple astigmatism; they may have different degrees of myopia or hypermetropia—compound as- tigmatism ; or one meridian may be myopic and the other hypermetropic — mixed astigmatism. The statement that the natural cornea is a section of a perfect sphere requires some modification, as, in point of fact, such a cornea is never met with. More or less astigmatism always exists; but, in the typical eye, the degree is so slight that it gives no inconven- ience, and it can be detected only by delicate tests. If Figure XVIII. (one of Dr. John Green's test dia- grams) be brought gradually towards the eye, it will be found that one set of lines remains distinct after those at right angles to it become blurred. Usually, the hori- zontal lines can be , iU Fig. XVIII. — Test for Astigmatism. seen closer to the eye than the vertical; at the ordinary reading distance, however, they should all appear alike. 84 EYESIGHT, AND HOW TO CARE FOR IT. Astigmatic persons, in reading, require different degrees of focusing for the horizontal and the vertical lines of the letters, and the distress that results from this continued and irregular strain of the muscle of accommodation may be readily understood. They usually attribute their defective vision to short-sight, but are disappointed in their efforts to correct it by short-sighted glasses, or by any glasses to be found in the stores. The surfaces of these glasses are spherical, and if they correct one meridian of an astigmatic eye, they cannot correct the other, but may make it worse. What is needed, in simple astigmatism, is a glass that will correct one meridian without affecting the other; and in compound or mixed astigmatism, a glass with two curved surfaces, one adapted to each meridian. Such a glass is found in the section of a-cylinder in- stead of the section o'f a sphere. Fig. XIX. represents d a cylindrical glass, and it will be seen that rays of light passing through its axis, a b, meet with no curve, and are therefore not refracted; while in the direction Fig. XIX. at right angles to the axis, c d, Cylindrical Lens. it ig strongly convex. This glass is cut into the usual oval form, and is set in the spec- tacle-frame with its axis corresponding to the direc- tion of the correct curvature of the cornea. In this way we are able to place the proper convex or con- OPTICAL DEFECTS. $5 cave lens before one meridian of the cornea, and, at the same time, only a plain glass before the opposite meridian ; or, if necessary, to correct each meridian separately by the appropriate curvature on each side of the glass. A difference of focus in the eyes of the same per- son is not uncommon. One eye may be correct, and the other long-sighted or short-sighted; they may have different degrees of the same defect, or one eye may be long-sighted and the other short-sighted. Sometimes, when the difference is very great, it is convenient to wear glasses that will adapt one eye to distant vision and the other to near. Irregular action of the external muscles of the eye- ball is closely connected with the subject of this chap- ter, as it is usually dependent upon optical defects. When we look at a distant object, supposing the eyes to be optically correct, the axes of the eyes are parallel, and the muscle of accommodation is at rest — the image is formed upon the retina, in accordance with the physical laws of optics, without the necessity for muscular action, and vision is without effort. When, now, we look at some small object near at hand, both eyes must be directed towards it (their axes converged) by the action of the muscles that move the ball, at the same time that the focus is correspond- ingly altered by the action of the muscle of accom- modation, increasing the convexity of the lens. 8 86 EYESIGHT, AND HOW TO CARE FOR IT. Here, then, is a closely associated action of the muscles on the outside of the eye, and the muscle of accommodation within it, that adapts the focus to the divergent rays of light coming from a near ob- ject ; and the comfort, ease, and safety with which the eyes may be used depends much upon the proper balance of these two forces. Their relation cannot be disturbed without more or less danger or incon- venience ; and such disturbance is a fruitful source of discomfort in cases of optical defect. In hypermetropia there is an excessive strain of the accommodation, out of proportion to the degree of convergence that is used; while in high degree's of short-sight an excessive convergence is demanded without any action of the muscle of accommodation, as the eye is already adapted to very near vision, and does not require an increase in the convexity of the lens. Squint. — The strain of the accommodative power in hypermetropia is the cause, in a great majority of cases, of squint, or "cross-eye." The demand for excessive accommodation causes an excessive tendency to convergence, which ends in a permanent turning inward of one eye. This kind of squint usually com- mences in children three or four years of age, or older, at the time when they begin to occupy them- selves with near objects, as toys and pictures, and to demand accurate vision. At first it occurs only when OPTICAL DEFECTS. $f the eyes are directed to some near object; then oc- casionally even when a distant object is looked at steadily or carefully, particularly if the child is not well, and is therefore less equal to the strain than usual; and, finally, one eye remains constantly turned in towards the nose. The origin of the squint is fre- quently referred to some attack of sickness, as measles, scarlet-fever, whooping-cough, or convulsions. This may be merely a question of coincidence, as these dis- eases occur very frequently at about the age when squint is developed ; or they may act as exciting causes, by reducing the strength of the patient so that the eyes are less able to bear the strain; but the real cause is a defect in focus, due to the fact that the eye is not properly formed — is not "according to measure." It will be remembered that when a want of har- mony in the action of the external muscles of. the eyeball causes the image to fall on parts of the retina that do not correspond, double vision at once results (see page 42). To avoid this annoyance, persons with squint learn to use only one eye, and the image on the retina of the other is said to be " suppressed." In consequence of this constant suppression, the vision of the squinting eye becomes greatly impaired, in fact, accurate vision is lost, though the eye remains perfectly healthy. In the early or periodic stage, before it becomes 88 EYESIGHT, AND HOW TO CARE FOR IT. constant, this kind of squint may be cured by cor- recting the optical defect with proper glasses, which remove the cause by taking away the strain. Of course, there are obvious difficulties in the way of this treatment in the case of very young children. It is worth some trouble, however, to remove so great a deformity without an operation, and, at the same time, to preserve the sight of both eyes, which is rarely, if ever, done by even the most successful op- eration, after the defect has been for some time estab- lished. After the squint has been cured by an opera- tion, there is danger of its return unless glasses are worn. In high degrees of short-sight, there is an excessive demand made upon the muscles that move the eyes inward (converge them), in the effort to keep them both fixed upon small objects held close to the face. Sometimes they prove unequal to this strain and give out, and one eye is turned outward by the opposing muscle, forming an external squint. The constant strain involved in the effort to over- come this tendency to external squint is prominent among the causes that increase short-sight, and when it cannot be relieved by suitable glasses, an opera- tion is sometimes necessary. This "insufficiency," as it is called, of the muscles that move the eyeball to do the work demanded of them, sometimes exists without short-sight. OPTICAL DEFECTS. 89 These are the principal, but not the only, causes of squint. A squint occurring suddenly, with double vision, is generally the result of paralysis of one of the external muscles of the eyeball, and is frequently the first symptom of serious disease of the brain. Such a case should receive immediate medical atten- tion. Weakness of the accommodation (or focusing power of the eye), giving rise to symptoms much the same as those of old-sight, but from a different cause, may occur in young persons with perfectly formed eyes. The act of accommodating the focus of the eye to near objects is accomplished by a muscle which is subject to local and general influences, like any other muscle of the body. In old-sight, this muscle is not necessarily weakened, but the lens becomes too dense to be impressed by it; in the cases now referred to, the muscle is at fault. After long illness, the muscle of accommodation shares the debility of the whole system, and the eyes are not fit for continuous close work any more than the legs are equal to a long walk. The use of the eyes should be moderate at first and gradually increased. After diphtheria, there is often a paralysis of this muscle, which is shown by difficulty or impossibility of reading, though the patient may be able to see perfectly well at a distance. It usually gets well un- der judicious treatment, though sometimes not for 8* gO EYESIGHT, AND HOW TO CARE FOR IT. several months. In the meantime, if there is no other objection to reading, proper glasses may be used. Spasm of the accommodation is also occasionally met with, usually in persons of nervous temperament or as a result of overstraining of the eye. The contin- uous action of the muscle of accommodation keep- ing the eye always focused for near objects, establishes a kind of artificial short-sight. Any short-sighted glass, even the weakest, does harm in such cases, as it gives sharpness of vision by stimulating the already overstrained muscle to increased action. Asthenopia, or weak sight, is the term applied to that state of vision in which the eyes, though their appearance is entirely natural and distant vision may be perfect, are more or less incapacitated for close work; they are unable to bear the strain of continued application to near objects. Asthenopia may result from any of the optical defects that have just been described, but its most frequent causes are long-sight (hypermetropia) and astigmatism. The demand made upon the eyes is excessive, and they prove unequal to it. The symptoms of this form of asthenopia have al- ready been briefly noticed. It is important to remem- ber that not only may those referred to the eyes be the least prominent, but the sufferer may not suspect his eyes at all, while the strain is manifesting itself by OPTICAL DEFECTS. 91 headache, dizziness, nausea, or nervous irritability, to such an extent as to excite apprehensions of serious disease of the brain. The possible results of asthenopia from short-sight, and consequent strain of the muscles that move the eyeball, are well illustrated by the following case, published in an English medical journal, five or six years ago, by Mr. Carter, a prominent ophthalmic surgeon of London. "The patient's father was a banker in a provincial town, and the son, who was an only child, had been intended to succeed to his father's business and social position. About eighteen months before I saw him, he was at Oxford, reading hard for honors, and with confident expectation of obtaining them. His work was suddenly interrupted by symptoms which compelled him to obtain medical advice, and which were attributed to some serious and alarming cerebral disturbance. He was directed to abandon his studies immediately, and not only to give up the idea of taking honors, but even to leave the university immediately, without aspiring to an ordi- nary degree. He returned home, and there the opin- ion given at Oxford was reiterated by his family atten- dant, and was confirmed by a consulting practitioner in the locality. He was for some time under treat- ment, but derived no benefit, and at last came to London for further advice. An eminent physician, since deceased, concurred in the view that had 92 EYESIGHT, AND HOW TO CARE.FOR IT already been taken of the case, and pronounced abso- lute rest of brain to be essential to the patient's re- covery. In order to obtain this rest, he was directed to undertake a voyage to Australia and back, and this direction he literally fulfilled. He went to Australia, made some brief stay there, and returned to England unimproved. He was then told that little or nothing more could be done for him ; that he must abandon the idea of carrying on the family business, or of taking any active part in life; and that he must also abandon an engagement of marriage which he had formed prior to his illness. His prospects seemed utterly blighted, and he listened to his father's nar- rative with a careworn and dejected expression which was pitiable to see. The father concluded by saying that he had heard, from an unprofessional source, that oculists were in the habit of using some instru- ment by which they could see the state of the circula- tion in the brain, and that he had come to me in the forlorn hope that this instrument might throw some light upon the case. " On inquiring into the actual condition, I was told that it was very'peculiar.' The memory, the intelligence, the mental faculties generally, were all unimpaired, and at last I narrowed the case down to this—that the patient was unable to read. Before he had read a page, he became the subject of double vision, followed by vertigo; and also, if the effort OPTICAL DEFECTS. 93 was continued, by sickness, palpitation of the heart, and intense headache. These were the symptoms that had interrupted his work at the University, and they had ever since recurred almost as soon as he opened a book. When he had not been trying to read, he was in all respects quite well. " On examining his eyes, I found that they were both myopic in the same degree, and that the far point was only eight inches from the cornea. The patient had binocular vision, and had never worn spectacles. With concave lenses of eight inches focal length, the distant vision was nearly normal. Beyond myopic crescents, the ophthalmoscope showed nothing amiss. "With these data, the condition of the case began to be manifest. The patient had never been able to read from a book which was more than eight inches from his eyes, and had generally held it still nearer, say at seven inches. The internal recti muscles, therefore, were required to maintain convergence of the two optic axes to a point only seven inches dis- tant. Up to a certain period they fulfilled this re- quirement, but they broke down under a stress of work which was imposed upon them by reading for honors. The muscles became tired, they relaxed sud- denly, and, as a matter of course, the two eyes being no longer directed to the same point of the page, the lines and characters would appear doubled. It is 94 EYESIGHT, AND HOW TO CARE FOR IT. probable that the whole system was somewhat over- wrought; but the transitions from double vision to vertigo, from vertigo to faintness, sickness, and pal- pitation, and from palpitation to headache, are easily intelligible. The muscles, having once struck work, rebelled against even a short period of convergence; and the grave view taken of the symptoms by medi- cal authority added anxiety and emotional excitement to the pre-existing elements of the case. "My prescription was very simple. I explained the view I took of the case, and told the patient he had nothing whatever the matter with him. I ordered two pairs of spectacles, one of eight-inch concaves, — to be worn from morning to night, except when read- ing,— and one of fourteen-inch concaves, for reading only. The book was never to come nearer than eighteen inches, and the patient was to read three half hours a day, at three different times, and to come and report himself in three weeks. He and his father listened to me with polite incredulity, but they probably thought the advice worth trying, and they procured the spectacles. On that day three weeks the young gentleman returned alone, his spec- tacles on his nose, his front erect, his whole figure expanded, his countenance beaming. He said : ' I have come to see you again because you told me to do so, but I have nothing to say except that I am quite well; I am going to be married next week, and OPTICAL DEFECTS. 95 to set to work at the bank as soon as we return from the wedding tour.' " Asthenopia sometimes exists without optical defect, in cases of disturbance of the general health, particu- larly of a nervous character. The external muscles of the eyeball or the muscle of accommodation act insufficiently, painfully, or irregularly; or the sensi- bility of the retina is easily exhausted, and any object looked at fixedly seems soon to fade away. In some cases, though the eyes do their part perfectly well, the mere mental effort involved in reading brings on a headache or dizziness that makes it impossible to continue. This form of the affection, however, is exceptional, and should never be admitted until a careful examination of the eyes has excluded every possible physical cause. The strain caused by optical defects is sometimes manifested only by an irritability of the eyes, or a slight chronic inflammation of the conjunctiva or lids. CHAPTER VII. SPECTACLES. THE simplest forms of spectacles are those used merely to protect the eyes from mechanical in- jury or excessive light. Plain, clear glasses are use- ful in employments that expose the eye to injury from flying particles. In many cases ordinary window- glass answers perfectly well, or, if greater strength is required, plate-glass may be substituted. As the latter is uncomfortably heavy, it has been recom- mended to use thin, clear mica instead. If greater protection is needed than can be given by at glass curved like a watch-glass, the best material for sides is wire gauze, as it allows the air to circulate about the eyes, and does not heat them so much or shut them up in an atmosphere saturated with secretions. Protecting glasses are not worn nearly so much as they should be. With the natural disposition to underrate any danger that we are exposed to con- stantly, many workmen prefer the risk of going with- out the glasses to the inconvenience of wearing them, and often bear the scars of innumerable wounds of 96 SPECTACLES. 97 the cornea. Generally, the only men who can be persuaded to wear protecting glasses are those who have already sacrificed one eye to their objections. For protection against the glare of too bright a light, green glasses were formerly used; but as the orange rays of the spectrum are thought to be the most irritating to the retina, the complementary color, blue, is now preferred. There is a serious objection, howeyer, to the long-continued use of any color in this way. The natural stimulus of the retina is white light, and glasses that decompose this leave the retina, when they are removed, unduly sensitive to the colors that have been excluded. The best glasses, in day- light at least, are the London smoke, or neutral gray, which, as nearly as possible, diminish uniformly all the light without separating its components. Those should be selected that are the most nearly neutral; some have a purplish tinge. Persons whose eyes are too sensitive to light find these glasses a great com- fort at the sea-side; in fact, it is only by their aid that many people can enjoy the benefits of sea-air, and their use in this way is entirely unobjectionable. As a rule, they should never be worn in the house, and never at any time when not absolutely necessary, as, by accustoming the eye to a subdued light, they may increase the difficulty that they are intended to remove. Blue glasses are more in order at night, as artificial light, particularly gaslight, has an excess of 9 G 98 EYESIGHT, AND HOW TO CARE FOR IT. yellow, and is pleasantly modified by blue, which ab- sorbs the yellow rays. Cheap protecting spectacles are often made of poor glass, and contain flaws which produce an unpleasant distortion of objects seen through them. " Coquille," or shell-glasses (those shaped like a watch-glass), if their surfaces are not parallel, may act as weak lenses to a noticeable and even annoying degree. To de- termine if a professedly plain glass is free from refrac- tion, hold it at some distance from the eye, and look through it at a window-sash across the room; when the glass is shaken from side to side, there should be no apparent motion of the sash. Ladies often find the protection of a double veil rnore agreeable than that of any kind of glass, and, in the case of children, the broad brim of a straw hat, ljned, if necessary, with dark silk or muslin, may an- swer perfectly well. Weak convex or concave spectacle-lenses may be made of blue or gray glass, but when the lens has a strong curve, a difficulty is met with in the fact that its thick part is necessarily darker than the thin. The sensitiveness of the retina is liable to be ex- hausted by long exposure to the dazzling reflection of sunlight from a wide expanse of snow. This is called snow-blindness. Alpine travellers who neg- lect to protect their eyes, sometimes suffer from it seriously. The Esquimaux guard against it by the SPECTACLES. 99 use of snow-spectacles formed of discs of wood with small holes perforated in the centres, which admit only so much light as is necessary for distinct vision. Though not very becoming, they are, perhaps, quite as efficient as anything that has been invented. The spectacle-glasses in most general use are double convex for long-sight and old-sight, and double con- cave for short-sight. They have the same curve on each surface. (See p. 34, Fig. VIII.) The periscopic glass is what opticians call a me- niscus. One surface is convex and the other concave, and it has the effect of a convex or a con- cave glass, according as one or the other of these surfaces has the sharper curvature. (Fig. XX.) The ad- vantage claimed for it Fig. XX.— A Positive and a Nega- is that the image is less tive Meniscus. distorted when the rays of light pass through it ob- liquely than is the case with the ordinary glass, and that, as there is less necessity for looking directly through its centre, the eye may move more freely behind it, and less turning of the head is required. There is no objection to its use, if it is found more convenient, but it has no optical advantage that can IOO EYESIGHT, AND HOW TO CARE FOR IT. compensate for its increased weight and additional expense. Prismatic glasses are used for the relief of the ex- ternal muscles of the eye. Fig. XXI. shows how it is possible to enable both eyes to see a near object Fig. XXI. —Divergent Rays made Parallel by Prisms. without converging. The prisms bend the rays of light towards their bases, and make divergent rays parallel. The degree of assistance given to the mus- cles in this way is regulated by the angle of the prisms. Prismatic glasses are sometimes used to cor- rect double vision. Cylindrical ox astigmatic glasses have been described. (See Fig. XIX.) Double focus glasses are sometimes used by persons SPECTACLES. IOI who need different glasses for reading and for dis- tance. They are so arranged that the upper halves of the spectacles are adapted to distant, and the lower halves to near, vision ; and they do away with the annoying necessity of frequently taking off one pair and putting on another. They are called Frank- lin glasses, because first used by Benjamin Franklin. He was slightly short-sighted, and therefore needed concave glasses for distance, and, as he grew older, also needed convex glasses to read with. He had too high an appreciation of the value of time to spend it unnecessarily in changing spectacles, and therefore cut a concave glass and a convex glass in half, and placing the concave halves above and the convex halves below, was always ready for either near or dis- tant sight. Sometimes, instead of using " slit glasses," the two required curves are ground, one on the upper half and the other on the lower half of the same glass. Spectacle lenses are usually made of crown- or flint- glass. The former is less expensive, but is softer and more easily scratched. Rock-crystal, or Brazilian quartz, is also used, and is commonly known as " peb- ble." It has no advantage over glass, except' in hardness; in fact, the opticians find it difficult, or impossible, to distinguish between them without a polariscope or a file. Many people, however, are not satisfied unless they have "pebbles," or think 9* 102 EYESIGHT, AND HOW TO CARE FOR IT. they have them, for glass is very often sold instead. What is essential in glasses is that they shall be per- fectly clear, of uniform density, and free from flaws, and shall be properly ground with the right curva- ture. These essentials are by no means always to be found in cheap glasses, so that spectacles are not good things to economize in. The kind of frame to be used is very much a matter of taste. It is important, though, that it should set properly, and that the glasses should be correctly centred, that is, that their centres should be opposite to the pupils. Sometimes, to produce certain effects, which it would be out of place to enter upon here, oculists order them decentred — the centres placed closer together, or farther apart, than the pupils. Theoretically, the use of eye-glasses, as compared with spectacles, is not to be encouraged, but practi- cally they will always be extensively used, and in most cases answer the purpose sufficiently well. There is usually more or less resistance to be over- come in wearing glasses constantly. In over-sight and astigmatism, the strain of the muscle of accom- modation, which has been established, perhaps, for many years, is not to be relaxed suddenly, or without persevering effort; while in short-sight, this muscle, which has never had any work to do, must learn to act. The change in the apparent size of objects, too, and in the estimate of distances is a source, at first, SPECTACLES. IO3 of perplexity and annoyance. Sometimes, when the degree of the optical defect is high, its full correction can be reached only by gradual approaches — by means of a series of glasses increasing in strength. In the case of any kind of optical defect, it is a great advantage to begin the use of glasses in youth, as the eyes adapt themselves to them much more readily then than in later years. The eyes and the glasses become, as it were, one optical instrument. The fallacy of supposing that the glasses that are most pleasant for three minutes are necessarily the best to use for years, is not so general now as formerly. Experience has taught the public much in this respect; but there are still many people who would scorn to buy a ready-made suit of clothes, but who still do not hesitate, in the infinitely more important and delicate matter of selecting glasses, to make their purchases without a measurement. CHAPTER VIII. PRACTICAL SUGGESTIONS FOR THE CARE OF THE EYES. ALL the organs of the body are better for moderate and rational use, and the eyes are no exception to this rule. Perfectly formed and healthy, eyes should do their work without the consciousness of their owner; and the test of this condition is that there shall be nothing to remind us that we have eyes. This would be a safe measure of the amount and kind of work to be demanded of them, for there is, even in health, such a wide range of individual differences in vigor and endurance, that what is safe or moderate work for one person may be dangerous excess for another. The great danger of people who have perfect and strong eyes, just as with those who have exceptional vigor of general health, is over-confidence. A French author, some years ago, wrote a book on " the ad- vantages of a bad constitution," in which he endeav- ored, with much ingenuity, and not without some support from facts, to show that its tendency was to 104 PRACTICAL SUGGESTIONS. 105 prolong life, by banishing recklessness and promoting caution ; and it cannot be denied that there are many people who would have had better sight in old age, if some slight weakness or defect had made them, in youth, more appreciative and careful of their eyes. It should never be forgotten that, while distant vision is a passive sensation not more exhausting than breath- ing, near vision demands convergence and accommo- dation, and therefore muscular effort. He who vol- untarily forces a continuance of this effort until it is no longer possible to see, is scarcely more rational than the fools of the " walking match," whose ambi- tion is to walk the greatest number of miles in the fewest number of hours that it may be possible to do and live. It is well in reading to interrupt the strain of con- tinuous gaze upon the page, and rest the eyes by looking into the distance .occasionally, even if only for a few seconds. In studying, or in reading any- thing that requires thought, this is likely to be done unconsciously ; the natural condition in close thought is rest of everything except the brain. Some of the biographers of Democritus assert that he put out his own eyes that he might devote himself more thor- oughly to meditation, undisturbed by the impressions of sight. One of the disadvantages of city life is the con- stant occupation of the eyes with close objects and 106 EYESIGHT, AND HOW TO CARE FOR IT. the absence of anything like a long, free range; those who are engaged in continuous and exacting city work experience an indescribable sense of rest when their eyes can be allowed to wander over a broad landscape or the boundless sea. A little fellow who had been taken to the country for the first time, on a Sunday-school picnic, pathetically illustrated this phase of city life, by exclaiming in raptures that " he never knew there was so much sky." He had seen only the little patch perpendicularly above the narrow court in which he lived, and whose pent-up limits comprised his world. He had never scanned the horizon, never seen a rainbow, or watched the flight of a distant bird — had never completely relaxed the tension of his eyes. It would be a wonder if, with a childhood alternating between this home and, per- haps, a crowded, ill-ventilated, and badly-lighted school-room, and a youth and manhood bound down to some close mechanical work, his eyes should be healthy and strong and well developed. Even the more prosperous dwellers in cities do not altogether escape this cramping tendency of town as compared to country, for nearly all their occupations, their bus- iness and pleasure, make a more or less constant de- mand upon the accommodative action of the eyes. It is their own fault, however, if this tension is not now and then relaxed; and not least among the ad- vantages of a holiday trip is the freedom from strain, PRACTICAL SUGGESTIONS. 107 the complete rest, that a distant range of vision gives the eyes. As distant vision represents rest for the eyes, and near vision represents exertion, care should be taken, in reading, not unnecessarily to increase this exer- tion by holding the book too close. The book should not be held nearer to the eyes than is necessary to make the print appear perfectly sharp and distinct, and no print should be read continuously that can not be seen clearly at about eighteen inches. Short- sighted persons may, of course, read closer than others without straining the accommodation; and persons advanced in life, in whom the lens has be- come less transparent and the retina less sensitive, have to hold small objects closer to get the benefit of a larger angle of vision, and therefore a larger retinal image. In the case of the latter, however, there is no longer a question of this kind of strain, as the accommodation of the eye to near vision is accom- plished by glasses, which also enlarge the visual angle and increase the apparent size of near objects. With- out any optical or other discoverable reason, or, per- haps, merely in consequence of a careless and loung- ing way of sitting, young people often acquire the vicious habit of reading with the book held close to the eyes—a habit which, if examination of the eyes proves it to be nothing more, should be strictly dis- couraged. It is very important, however, to deter- 108 EYESIGHT, AND HOW TO CARE FOR IT. mine positively that there is no physical cause for the habit, and to remember that true short-sight depends upon the form of the eyeball, which no amount of discipline can alter. Great injustice is often done to children by accusing them of obstinacy or inatten- tion, when they are the subjects of physical defects of sight or hearing. Those with a high degree of long- sight are particularly liable to be misunderstood, for, though they can see distant objects better than near ones, they sometimes hold the book close to the eyes to make the print appear larger, and thus partially compensate for their dimness of sight. In such cases, the retinal image, of course, becomes more indistinct the nearer the object is approached to the eye, but, as Prof, von Graefe showed by mathematical calcula- tion, it gains more in size than it loses in sharpness of outline. Children with astigmatism often appear stupid or inattentive, because there is in this defect what the subjects of it sometimes aptly call "slow sight," that is, they do not recognize a word quickly on first sight, but " it seems to come to them after- wards." As has already been explained, the cause of this is that the perpendicular and the horizontal lines of the letters have a different focus, and a men- tal effort is required to combine them. When the sensitiveness of the retina becomes exhausted from fatigue or other cause, the impression of a larger PRACTICAL SUGGESTIONS. IO9 image is required, and the book is held closer to the eyes: it should be laid aside instead. A very common way of straining the accommoda- tive apparatus of the eye is by reading in a car or carriage. Between reading under these circumstances and reading in a motionless seat, there is all the dif- ference between irregular and jerky muscular action and continued uniform muscular tension. A mod- erate and accustomed muscular tension, when once established, may be continued a long time without conscious effort or perceptible strain ; but the case is very different with continually varied degrees of con- traction. A weight that can be carried for miles without fatigue, may be found very exhausting if picked up and set down every few seconds for the same length of time. Ordinarily, when we take up a book to read, we adapt the focus of our eyes to a cer- tain distance, and maintain a nearly uniform tension; but when we jead in a car, the focus must be changed to suit every variation that the jarring makes in the distance between the eyes and the book. The exter- nal muscles, too, are strained in the effort to keep the eyes fixed upon the letters in their irregular move- ments. Business men who live out of town find a constant temptation to this imprudence in the morn- ing and evening papers. Some people may be able to stand it without serious injury — just as some octo- genarians will tell you that they have smoked all day 10 HO EYESIGHT, AND HOW TO CARE FOR IT. and a good part of the night for more than sixty years; but, on general principles, it is not a good thing to do. Another equally, or perhaps more, injurious habit is that of reading while lying down. The extraor- dinary strain, in this case, falls, not upon the mus- cle that adapts the focus of the eye, but upon the external muscles of the eyeball that direct the eyes to the print. To direct both eyes to the same point requires a delicately balanced associated action of several muscles of each eye. In any part of the body, where a certain set of muscles are accustomed to act together in a given direction, this particular combi- nation of movements becomes natural and easy, and any other comparatively difficult. This may be ap- preciated, for instance, by any one who has under- taken to drive a nail into the ceiling, and has ex- perienced the fatigue of the muscles of the arm and neck and back that follows almost immediately. We are accustomed always, in converging the eyes towards any small object, at the same time to direct them downwards, as the object is usually held in the hand, or lies on something before us, below the level of the eyes. This facility of turning both eyes in- wards and downwards at the same time has not only been acquired by the individual, but has been in- herited from his ancestors, and has become a part of his nature; so that the association of convergence PRACTICAL SUGGESTIONS. Ill with any other than a downward movement demands an extraordinary effort. This is a cause of fatigue in looking at pictures hung high in a gallery. Con- siderable interest has been excited recently by an affection noticed in miners, and called "miner's nys- tagmus," in which the external muscles of the eye- ball seem to lose their balance, and the eyes con- tinually oscillate. It is thought to result from the unnatural position of the eyes in working at the roof of the subterranean cavern in which these men pass their lives. In reading while lying down, it is hardly possible to hold the book in a favorable position, and the ex- ternal muscles of the eye are strained. In addition to this, when the head is on a level with the body, instead of erect, there is a tendency to an excess of blood in the eyes. It is not well to persist in reading when overcome with sleep, as there is a constant tendency of*the muscle of accommodation to relax, and of the eyes to diverge, and they have to be forced back to their work by an effort of the will. The effect of this is soon shown in a congestion of the blood-vessels of the conjunctiva. As tension of the eyes in near vision is the prin- cipal cause of strain and fatigue, and the various dis- eased conditions that they bring about, common sense will dictate that the objects upon which near vision 112 EYESIGHT, AND HOW TO CARE FOR IT. is exercised should be such as not to make excessive or unnecessary demands upon this tension. ' By far the most universal of these objects are printed letters ; and as small print or poor print must be brought closer to the eyes to be distinctly recog- nized, it adds proportionately to the tension required, and is a fruitful source of injury. It is not easy to fix an arbitrary size for letters, as much depends upon their kind and form. The letters need to be larger if the strokes are fine, while heavier strokes may be easily recognized, if the print is clear, even in smaller letters. German letters are trying because of the extreme fineness of some of the lines that form them. In reading, it is not usually necessary to see sharply all the details of the letters, as, if the characteristic parts are distinct, the rest is recognized, and the whole word is suggested rather than accurately seen. Let- ters may be readable without being distinctly visible. This is well illustrated by what are called IVOR- MAN" CAPITALS, in which the characteristic strokes are excessively heavy, and the others but lightly traced. The names of the streets in Paris are printed in this type, and can be read at a greater distance, and by a dimmer light, than would be possible with any other kind of letters of the same size. The space be- tween the different parts of the letters, between ad- joining letters, and between the lines, is also to be considered. PRACTICAL SUGGESTIONS. II3 In the test-types used by oculists, letters seen at an angle of five minutes are adopted as the smallest that can be distinctly seen by the average eye. As the limbs and subdivisions of these letters measure one- fifth of their height, this gives an angle of one min- ute as the limit of accurate perception by the retina. According to this standard, the smallest letter recog- nizable at twenty feet would be about three-eighths of an inch in height, and at eighteen inches about one-thirty-second of an inch. The following paragraph, from Dr. Snellen, of Utrecht, the author of the test-types in general use, gives a specimen of letters one-thirty-second of an inch in height: " We have adopted as proper objects square letters, the limbs of which have a diameter equal to one-firth of the letters' height. Such letters are clearly distinguished by a normal eye at an angle of five minutes. As the limbs and subdivisions of the letter just measure one-fifth of their height, they present themselves at an angle of one minute; for instance, our letter, C, shows an opening, as compared with the O, of one minute visual angle. In testing accuracy of vision, we accept perfect recognition, and not uncertain perception, of the letters.'' As in ordinary letters the width of some of the strokes is much less than one-fifth of the height of the letter, a larger letter than this would be required for distinct vision. Of course, for continuous read- ing, the letters should be very much larger than those that it is just possible to see. Nor should type be made with reference only to perfect eyes and good daylight, as a vast amount of reading is done in arti- ficial light and by imperfect eyes. 10* H 114 EYESIGHT, AND HOW TO CARE FOR IT. The quality of type is to be considered as well as the size, for print of fairly good size is often very trying to the eyes, because blurred and indistinct. The quality of the paper, and of the ink, too, has its influence on the general effect. Bright white paper, particularly if its surface is glazed, is dazzling and irritating. It is on account of the quality, rather than the size, of English print, that it is usually so much pleasanter to read than American. Some cheap publications manage to combine all of the defects referred to in such a degree that a more paternal government than ours might well suppress them as enemies to society. Fortunately, such pub- lications do not contain intellectual treasures that it need tempt one to risk his eyes to reach. As the eyes must be moved, in reading, to bring the image of each word in succession upon the yellow spot of the retina, if the page is very wide, the ex- ternal muscles of the eyeball are fatigued by follow- ing the long lines, and it is better to divide such pages into double column. The whole aim and object of the eye, with all its complicated anatomical, physiological, and optical apparatus, is to receive the impressions conveyed by light; and it is hardly necessary to urge the impor- tance of considering the amount and kind and direc- tion of the light in which and by which it must do its work. Though it is, of course, possible to use too PRACTICAL SUGGESTIONS. I I 5 bright a light in reading, there is much more danger of the opposite extreme, and it is only necessary, in this direction, to avoid a dazzling or an irritating glare. It is not often that daylight indoor? is too bright to read by — the direct rays of the sun being, of course, avoided — but too little light is a real and very common grievance. The distinctness of an ob- ject depends upon the amount of light reflected from its surface as well as upon its size; and to diminish the light by which it is seen is, so far as the eye is concerned, the same thing as to diminish its size. An increase in the size of the retinal image is at once required, to compensate for its dulness; to gain this increase, the object is brought closer to the eye, and the converging and focusing power is put upon the strain. Much injury is done by reading in twilight, and by reading or working in badly-lighted rooms. Good artificial light is much to be preferred to in- sufficient daylight. The direction in which the light comes is by no means a matter to be disregarded. All light that does not come from the page, in reading, can only be a source of annoyance, by irritating the retina, if it is direct, or by confusing the image of the print with the images of other objects, if it is reflected. The irritating effect of direct light, even in distant vision, is shown by the pulpit-lights in church or the foot-lights in a theatre; and the confusion caused by Il6 EYESIGHT, AND HOW TO CARE FOR IT. the interference of the images of other objects, may be illustrated by looking at a picture hung in the space between two windows, where it will be seen to great disadvantage, because its image on the retina has to contend with the images of the window-sashes, or of objects outside. We should therefore place ourselves in such a position that the direct light from the win- dow will fall upon the book from above and from the side — preferably the left side, as, particularly in writ- ing, a shadow is cast by the hand if the light comes from the right. The next best direction is, perhaps, from above; if from behind, a shadow is cast by the head and shoulders. The worst direction of all is that directly in front; indeed, this is so manifestly and immediately uncomfortable, that it is scarcely necessary to inveigh against it, as no one ever adopts it from choice. Light coming from below the level of the head is worse than useless, and, if the windows are low, it is often an improvement to darken the under sash. From an optical point of view, it is a mistake to place the shades at the top of the window instead of at the bottom. The natural stimulus of the retina is white sunlight, and this is, of course, the best kind for the eye to work with. The softest and most pleasant of all light is the diffused light from a northern sky; but the point of the compass is not a matter of paramount importance, provided the light is sufficient in amount PRACTICAL SUGGESTIONS. WJ and is free from annoying reflections. An excess may be easily regulated by shades, and is therefore the safest of all faults. The demands that the labors and pleasures of civilized life make upon the eyes, however, cannot be met by daylight alone, and during many hours of the twenty-four an artificial substitute must be found. The nearer an artificial light can be made to approach to the perfectly colorless daylight the better, but the most important requisites are that it shall be suffi- ciently bright and shall be steady — a flickering light is always bad. Gas-light has a decided excess of yellow rays, but is almost universally used in cities, and answers very well if the gas is of good quality and the flame is properly regulated. The flame of an ordinary "fish-tail" burner, exposed to every current of air, is never steady, and is unfit to read by. The shades or "globes" of a recent pattern, with wide openings at the bottom, have something of the effect of a chimney, and make the flame more steady. The Argand burner, with its shade and chimney, gives an excellent light and is easily controlled. The light of a good coal-oil lamp, particularly of that known as the "German student's lamp," is more grateful to the eye, and is used by many persons in preference to gas. A slight tinge of blue in the shade or chimney of a gas-flame modifies the light pleasantly by absorb- ing the excess of yellow rays. We cannot think, without wonder, of the literary Il8 EYESIGHT, AND HOW TO CARE FOR IT. work that our ancestors did by the light of tallow- candles or of "midnight oil," that we would think it a hardship to read by for an hour. Perhaps the retina accustomed to the glare of the nineteenth cen- tury needs a brighter light than theirs-did. The "coming" light is undoubtedly the electric. Among its many advantages is the fact that in color, or rather absence of color, it more nearly approaches daylight than any other. Its spectrum is nearly like that of sunlight. Though it has already been suc- cessfully applied to the lighting of large areas, its application to domestic purposes has so far proved impracticable, on account of difficulties in the way of dividing the electric current so as to produce a number of small lights instead of a single intense one of dazzling brilliancy; but, having made such wonderful strides of progress in the last three or four years, it is not going now to stand still always, even in the presence of the difficult problem of " di- visibility." The restless and irresistible spirit of invention is hard at work, and has been heard from last in San Francisco, where it is proposed to illumi- nate a whole building, or even a street, by one lamp, the light from which is to be directed by lenses and reflectors, and to be conveyed by tubes, like gas or water, to as many points as may be desired. The same general principles are to be observed in the care of weak eyes as of strong ones; but as the PRACTICAL SUGGESTIONS. 119 penalty of excess or imprudence is more swift and sure, there is more urgent necessity for moderation and prudence. A great deal of work may often be done by weak eyes, if there is no actual disease, pro- vided they are not urged beyond the limits of their endurance. The amount of work demanded of them should be proportioned to their strength. It should first of all be determined how much of their weak- ness may be due to optical causes, and how much re- lief may be derived from glasses; and they should then be given the benefit of greater care, more rest, more indulgence in distant vision, and more hours of sleep. Many eyes that are equal to all the rational demands of business, social, and domestic life, will inevitably break down if called upon to bear the strain of daily work, and also to pass the best part of the night in the glare and heat and dust, the close atmosphere, late hours, and excitement of the ball- room and theatre. The principle of the familiar adage of " mens sana in corpore sano," is as applicable to the sight as to the mind, and a person whose whole system is debili- tated should not expect full duty of his eyes. CHAPTER IX. EFFECTS OF SCHOOL-LIFE UPON THE SIGHT. THE principles to be observed for the preservation of sight are, of course, the same in the case of children as of adults, and in school-work as in other occupations; but the greater necessity for carefully observing these principles at the time when the body, as well as the mind, is rapidly developing, and their very general neglect at this critical period, may jus- tify a more detailed reference to them, even at the expense of some repetition. The increased demand that the exigencies or the fashion of the times make upon the eyes as well as upon the brains of children, and the increased numbers that are yearly brought within the influence of school-life by the compulsory laws of governments or of public opinion, should be accompanied by a corresponding increase in the use of all the alleviations and precautions that science and humanity can suggest. School-life is essentially an unnatural one; school-training is necessarily an artificial process, and unless it is conducted under rational and favorable conditions, universal education 120 EFFECTS OF SCHOOL-LIFE. 121 can never be an unmixed universal blessing. M. Javal, of Paris, in a recent essay on the physiology of reading, says, "The necessity of reading with an increased assiduity, and at a more and more tender age, print whose fineness has been increasing from generation to generation, has resulted in generalizing myopia to such a degree, that if means of precaution are not taken this defect will end by affecting the whole human species." The cramming for "exhibitions," and what Pro- fessor Huxley calls the "abomination of desolation " of competitive examinations, prizes, etc., that goad on children of various strength and capacity to tasks that the brightest and strongest are hardly equal to, are responsible for much injury of mind and body as well as of sight; and the "higher education," that is now so earnestly demanded for the gentler sex, is too often dearly bought at the expense of shattered constitutions and unstrung nerves. But if these things must be, in the name of humanity and justice, let them be surrounded by all the checks that can lessen their power for evil. A matter of much importance, and one that is very generally neglected, is the air that children breathe in school. The carelessness or ignorance of public officials, or the narrowest possible considerations of economy, very often huddle an excessive number of children of the poorer class into small and ill-venti- ii 122 EYESIGHT, AND HOW TO CARE FOR IT. lated public schools; but this class are by no means the only sufferers, as the greater proportion of private schools are held in houses not intended for the pur- pose, and parents who give every care to the sur- roundings of their children at home, often seem strangely indifferent to the fact that they may spend many hours of the day, with twenty or thirty others, in a close and superheated little room that was built, perhaps, for five or six people to dine in. This is a fruitful source of income to the family physician, and now and then brings a case of weak sight, from de- bility and nervous exhaustion, to the office of the ophthalmic surgeon. As the sense of sight is the chief medium of edu- cation, it is hardly possible to overestimate the im- portance of feeling assured that its organ is in proper working order, and that whatever defects Nature may have left in it have been, so far as possible, remedied by art. Though great advance has, of late years, been made in this direction, much still remains to be done, and many children, in the critical period of school-life, labor under disadvantages that a little care and attention might easily remove. The case of children with long-sight is particularly liable to be misunderstood, because their stronger power of accommodation, — their greater ability to change the focus of the eye by increasing the convex- ity of the lens,— enables them to mask a degree of this EFFECTS OF SCHOOL-LIFE. \2% defect that would manifest itself in after-life by an absolute inability to read, or even by dimness of dis- tant vision. It will be remembered that the axis of the long-sighted eye is too short (see page 73), and it has been explained how the optical defect of this malformation may be neutralized by a corresponding shortening of the focal distance — bringing the focus forward by increasing the convexity of the lens. What we are concerned with here, is the fact that in childhood the soft lens admits of a much higher de- gree of this change of form, and makes it possible to see, and to see distinctly, in spite of the defect. This, however, is accomplished by muscular strain, and demands a certain amount — sometimes a very considerable amount, depending upon the degree of the defect — of physical and mental effort. Such a child may be said to be " weighted " in the race with his classmates; he may be able, by virtue of superior strength or greater pluck, to keep up with the rest, or even to take the lead; or he may break down before the end of the race is reached. He seeks a bright light to get the sharpest possible image of the print, and may get on well enough in the morning, when he is fresh and vigorous, and light is abundant, but suf- fers most in the latter part of the day, when the light grows dim, and he is more or less fatigued. A bright light assists him, too, by contracting the pupil, and thus excluding the outer rays of the cone of light 124 E YESIGHT, AND HO W TO CARE FOR IT. which make the most confusion in the retinal image. He sometimes learns to increase this effect at night by holding the light between his eyes and the book. A dislike of books sometimes originates in the extra effort required to read them, and an appearance of stupidity or inattention may have the same phys- ical cause. Support is given to this view of the case, by the fact that the difficulty of distinct vision varies decidedly at different times, not so much with moral moods as with variations in mental and physical vigor. As has already been explained, four-fifths of the cases of internal squint are the result of hypermetro- pia, or long-sight, and this great deformity, which is increased by use of the eyes, may generally be pre- vented, and sometimes cured, by proper and timely correction of the optical defect. The eyes of children with this defect are usually '' weak,'' and become watery and bloodshot after pro- longed use. The edges of the lids are often thick- ened and red. Finally, the constant strain, excessive even for distant vision and painfully so for near, is a frequent cause of headache and other nervous symp- toms. In astigmatism the difficulties are still greater, and, in high grades, cannot be, even temporarily, entirely overcome. Even with the greatest amount of strain, vision is never quite distinct. Professional men of EFFECTS OF SCHOOL-LIFE. 125 middle age, who have all their lifetimes been at work with books without correction of this defect, are heard to say, when provided at last with cylindrical glasses, " this is the first time I have ever seen print distinctly." Children with long-sight or astigmatism often struggle on for years under painful disadvantages, until finally they break down utterly, and an oculist is consulted to decide whether they had better give up school. Of course, they need glasses, and are old enough to wear them if they are old enough to study. They may not be becoming, but neither are headache, bloodshot eyes, wrinkled eyebrows, half-closed lids, or a squint — any or all of which may be the only alternative, so far as personal appearance is concerned, to say nothing of the importance of continuing their education with comfort and safety. Many people of a conservative turn of mind are greatly shocked at the degeneracy of the times, and the multiplicity and officiousness of eye-doctors, when they see a child with spectacles ; ignoring the fact that such children, in the good old times when they themselves were young, were compelled to give up study altogether, or to struggle painfully and irregularly for a partial education. As might have been expected from what has gone before, the most frequent of the injurious effects that follow tension of the eyes prolonged unduly, or under 126 EYESIGHT, AND HOW TO CARE FOR IT. unfavorable circumstances, is short-sight. The high- est authority upon this subject, Prof. Donders, of Utrecht, says: "The distribution of near-sighted- ness, chiefly in the cultivated ranks, points directly to its principal cause — tension of the eyes for near ob- jects. Respecting this fact, there can be no doubt. " Three factors may here come under observation : ist, pressure of the muscles upon the eyeball in strong convergence of the visual axes; 2d, increased press- ure of the fluids, resulting from accumulation of blood in the eyes in the stooping position ; 3d, congestive processes in the eye v/hich, tending to softening, give rise to extension of the membranes. Now, in con- nection with the causes mentioned, the injurious effect of fine work is, by imperfect illumination, still more increased. " To this it is to be ascribed that in schools where, by bad light, the pupils read bad print, or write with pale ink, the foundation of near-sightedness is mainly laid, which, in fact, is usually developed in these years.'' These causes may not only increase to excess a slight degree of short-sight or develop an hereditary predisposition to the defect, but may produce it in an eye originally perfect. It has been positively es- tablished by careful and extensive statistics that short- sight is most frequently, if not almost exclusively, developed during school-life. This is due partly to EFFECTS OF SCHOOL-LIFE. 12J the fact that the eye during the period of its growth is more liable to change of form, and partly to the fact that children have a much stronger power of ac- commodation than adults, and therefore hold objects much closer to the eyes; but, to a great extent, it is due to preventable causes that are too often over- looked by parents and teachers. The dangers to be avoided are : a too prolonged tension of the eyes, concentration of the sight upon objects too near, and straining of the external mus- cles of the eyeball by a position of the book or paper unfavorable to their free and natural movement. It is important in all cases, and particularly if a tendency to short-sight is known to exist, not to urge or to allow children to keep the eyes fixed upon the book too long without intermission ; this is not an imaginary danger, when a certain task is to be accom- plished in a given time. No form of punishment that involves this kind of strain should ever be adopted. The book or paper should never be closer to the eyes than ten or twelve inches, and if there is short- sight enough to prevent the letters from being distinct at this distance, it is usually better to wear proper glasses in studying. The print should, of course, be large enough and clear enough to be seen with ease at a much greater distance, and it is important that pale ink should not be used in writing. (See page 113.) 128 EYESIGHT, AND HOW TO CARE FOR IT. Reducing'the size of print has much the same effect as diminishing the amount of light, as the smaller the print the more light necessary to make it distinct, and the closer it is brought to the eye. This is appreciated at the commencement of old-sight, when fine print can be read only in a bright light, because the loss of accommodating power prevents us from compensating for the smallness of the type by bringing it closer to the eyes. Children are able to do this, but they do it at the expense of a strain that may inflict permanent injury upon the eyes. Printers' type, particularly for school-books, is a bad thing to economize in. The cause that most frequently necessitates a too near approach of the book is a defect in the amount or direction of the light. Dr. Cohn, whose statistics of the examination of more than ten thousand school children in Germany have already been referred to (seepage 79), found that "the narrower the street in which the school was built, the higher the oppo- site buildings, and the lower the story occupied by the class, the greater was the number of near- sighted children; " he also found that, while in the village schools the proportion of near-sighted pupils was only 1.4 in a hundred, in the city schools it was 11.4 per cent. It is impossible to establish any general and uniform measure for the proportionate size of windows, as so EFFECTS OF SCHOOL-LIFE. 129 much depends upon the point of the compass from which the light comes, and, particularly, upon the character and the proximity of surrounding build- ings ; but it should always be remembered that an ex- cess of light is easily controlled, while a deficiency is an irremediable defect. Dr. Cohn, in a recent pub- lication, maintains that a school-room cannot have too much light, and recommends the very large pro- portion of a square foot of window-glass for every square foot of floor, and says that less than about half this proportion should never in any case be allowed. Some other authorities consider the pro- portion of thirty to one hundred usually sufficient. The direction of light is scarcely less important than the amount. Much discomfort may be caused by shadows thrown upon the book or paper by the shoulders, head, or hand, but the most injurious direction for light to come from is that directly in front. Such a light not only causes a close approach to the desk, by bending over to shade the eyes from the glare by the brow or perhaps by the hand, or turning of the head to one side, which brings one eye nearer to the work than the other, but the dazzling has a directly irritating effect upon the retina and conjunctiva. It is extremely annoying to the strong- est eyes, and is intolerable to persons whose eyes are weak or unduly sensitive. There is rarely any excuse for this mistake, as it is nearly always possible to I I3O EYESIGHT, AND HOW TO CARE FOR IT. place the desks or seats in such positions as to avoid it; but it is still not uncommon to see class-rooms or study-rooms, even in buildings erected especially for school purposes, in which the only comfortable and safe pair of eyes is the teacher's. The conditions to be observed are simple enough ; the room should be oblong, and be lighted by high windows in one of the long sides, and the rows of desks should be parallel to the short sides, and should face so that the light may come from the left. A large, square room, with windows on two or more sides, can never be properly lighted. In erecting a building for school purposes, it in- volves little or no additional expense to provide win- dows of sufficient size, and in utilizing a house built for other purposes it is usually possible to enlarge the windows, if necessary. The majority of school- houses are, at best, not models of architectural beauty; and, at any rate, this is a matter of secondary con- sideration where such grave practical interests are involved. Further, it should be remembered that "there is an architecture for schools as well as an architecture for palaces. One is not less worthy of study than the other, and we are at fault in taste as well as in hygiene if we forget that here real beauty consists, above all things, in the perfect adaptation of a building to its uses." In some Austrian and Swiss schools the plan has been adopted of fixing EFFECTS OF SCHOOL-LIFE. 131 shades at the bottom of the windows, so that they may be unrolled upwards instead of downwards. By this arrangement, when light is excessive, it can be modified by excluding the portion that is less useful and agreeable, and admitting only that which comes from above. Light striking below the top of the desk can reach it only by reflection, and is uncertain and confusing. At night, a number of desks cannot be lighted to advantage by any one source of light, however brill- iant. The same rule as to direction should, of course, be observed as in daytime. Liebreich recom- mends the use of reflectors, and suggests that they might be so arranged as to act, at the same time, as ventilators. The vitiation of the atmosphere by the combustion of a number of lamps or gas-jets is not to be lightly considered. Ground-glass globes are condemned by all authorities as unsuitable for school purposes. The very property that makes them useful for the general lighting up of a room, that of diffu- sion, unfits them for this use. The size and form of the desk, and its relation to the seat, are not without their effect upon the welfare of the eyes. To use desks and seats of the same pattern and size for a large number of children of all ages, is not more rational than the system of distri- bution of army clothing, by which, as Dickens com- plained, all the tall soldiers got the short pantaloons, 132 EYESIGHT, AND HOW TO CARE FOR IT. and the short soldiers got the long ones. If a child is uncomfortably seated, he is pretty sure to lean for- ward on the desk, thus bringing his eyes too close to their work, and, at the same time, overfilling their blood-vessels by gravitation. As the muscles of the back become fatigued by sitting long in a constrained position, the tendency is to bend over more and more, and this faulty posi- tion, at first assumed for temporary relief, becomes, by frequent repetition, a confirmed habit, and may end in permanent deformity. Thus a relation is es- tablished between short-sight and spinal curvature, and either may promote or increase the other. Another affection of the eyes that may result from improper arrangements for study, is that known to ophthalmic surgeons as" muscular asthenopia," a dis- turbance of the harmonious action of the muscles that move the eyes and direct them both to the same point of the book or paper. (See page no.) An excessive convergence to an object too close cannot be main- tained without injurious strain, and a direction of the axes of vision upwards or sidewise demands an un- natural, and therefore fatiguing, combination of mus- cular actions. It will be readily understood how the positions often assumed by children at school must necessitate one or even all of these conditions. According to Liebreich, the most common and im- portant defects in school furniture are the following: EFFECTS OF SCHOOL-LIFE. 133 " 1. Want of, or unsuitable, backs. "2. Too great a distance between the seat and the desk. "3. Disproportion, generally too great a distance, between the height of the seat and that of the desk. '' 4. Wrong form and slope of the desk.'' Illustrations of model desks and seats, proposed by Liebreich for remedying these defects, may be found in his lectures on school-life.* "The back ought to be straight, and consist of a piece of wood only three inches broad. If this is fixed at a proper height, viz., close above the hips, it supports the loins sufficiently to make it easy and comfortable for even the most delicate children to sit perfectly upright. The seat ought to be broad enough to support almost the whole length of the thigh, and the height of the seat such as to allow the sole of the foot, in its natural position, to rest on a foot-board. The edge of the desk must be perpendicularly above that of the seat, and just high enough to allow the elbow to rest upon it, without displacing the shoul- der." A flat desk promotes a stooping position, with its attendant evils of close sight and gravitation of blood to the eyes, and, besides, does not permit the di- *The subject of "School Hygiene" will be treated in a future number of the Primers. 12 I34 EYESIGHT, AND HOW TO CARE FOR IT. rection of vision most favorable to the natural and easy movement of the eyeballs. An inclination of forty or forty-five degrees is considered the best for reading, as, when the body is erect, and the eyes are directed downwards and forwards, this brings the page about at right angles with the line of vision. This slope would be too steep for writing, and an an- gle of about twenty degrees is recommended. The inclination of the desk may be changed by a very simple mechanism. Still more serious considerations (which it would be out of place to discuss here) are involved in this question of the construction of desks and seats. A dis- tinguished orthopoedic surgeon, Eulenberg, has stated that ninety per cent, of curvatures of the spine, not induced by local disease, are developed during school- life ; and a number of high authorities have testified to the sad effects that crooked and stooping posi- tions at school may have upon the heart and lungs and abdominal organs as well as upon the spine and the sight. INDEX. PAGE Accommodation of Vision to Different Distances . .41 ----Paralysis of ........ 89 ----Spasm of........ .90 Acids, Injury of the Eye by......52 Albino..........15 Amaurosis.........60 Aqueous Humor........20 Artificial Eye........53 Asthenopia.........9° Astigmatism .........82 Beam of Light........33 Belladonna, Effects of, on Eye.....17 Binocular Vision ........ 42 Black Eye.........21 Blind Spot on Retina.......42 Camera Obscura........31 Cataract ..........59 Catarrhal Ophthalmia.......54 Chinese Eye.........27 Choroid.........14 ----Diseases of . . . . . . • . .60 Ciliary Muscle........18 Coin Experiment........33 135 I36 INDEX. PAGE Color-Blindness ....'..•• 61 Color of Eye......• • • *5 Commissure of Eyelids.......26 Conjunctiva ......••• 2° Cornea..........*3 ----Diseases of........57 Crystalline Humor.......2° Daltonism ......... 63 Diphtheria, Paralysis of Accommodation in . . . 90 Diphtheritic Conjunctivitis......57 Distance, Estimation of. . . . . . • 44 Distant Vision.........38 Double-Column Print......."4 Double-Focus Glasses.......100 Double Vision ........ 43 Egyptian Ophthalmia.......55 Electric Light........118 Emmetropic Eye ........72 External Muscles, Affections of.....85 Eyeball..........12 Eyebrows.......• • . 22 Eyeglasses........ 102 Eyelashes...... . • • 25 Eyelids...........23 Eye-stones.........50 Focus . ........33 ----of Divergent Rays......40 Foreign Bodies in Eye.......50 INDEX. 137 PAGE Glasses, Convex and Concave.....99 ----Cylindrical........100 ----Double-focus.......loo ----Periscopic ........ 99 ----Prismatic ........ 100 ----Slit..........101 Glaucoma.........59 Granular Lids.........54 Heredity in Eye Diseases......65 Humor, Aqueous ........ 20 ----Crystalline ........ 20 ----Vitreous ......... 19 Hypermetropia...... . 71 Image, Formation of, by Convex Lens . . . • 34 ----in Eye.........35 ----Inversion of, on Retina......35 Iris..........15 ----Inflammation of.......58 Jacob's Membrane. . . . . . . . 19 Lachrymal Apparatus.......27 Lens, Crystalline ........ 20 Light, Artificial........117 ----Beam of........33 ----Electric.........118 ----in Reading......• .114 ----in Schools........128 ----Ray of.........3' ----Refraction of........32 Lime, Injuries of the Eye by.....52 12* 138 INDEX. PAGE Measles, Affections of the Eye in.....57 Membranes of the Eye . . . . . . . 12 Meniscus .......... 99 Muscse Volitantes........61 Muscles, External, of Eye-ball......29 Muscular Insufficiency.......88 Myopia .......... 77 Ophthalmia, Purulent . . . . . . . 55 ----Sympathetic ........ 53 Ophthalmoscope ........ 46 Opium, Effect of, on the Eye . V . . . .17 Optic Nerve ......... 19 ----in Diseases of Brain ...... 48 Orbit..........21 Paralysis of Accommodation ...... 89 Pebbles.........101 Physiology of Vision.......31 Pupil..........16 Retina..........18 ----Diseases of........60 Retinitis Pigmentosa.......67 Scarlet-Fever, Affections of Eye in . . . . 57 School-Desks . . . . . . . . .130 Sclerotic ......... 12 Sight, Long ......... 71 ----Old.........68 ----Second........ . 69 ----Short.........77 ---Weak ......... go INDEX. 139 9 PAGE Slit Glasses.........101 Small-Pox, Affections of the Eye in.....57 Snow-Blindness........98 Spasm of Accommodation......90 Spectacles, Blue ........97 ----Coquille ......... 98 ----Protecting........97 ----Smoked.........97 ----Snow.........99 Squint.........3°. 86 Sympathetic Ophthalmia.......53 Tapetum Lucidum.......J7 Tears..........28 Tobacco Amaurosis . .....60 Type..........II2 Vitreous Humor....... • • l9 Weak Sight.........9° Wild Hairs.........25 Winking..........24 Yellow Spot of Retina.......37 The End. SELECT LIST OF BOOKS FOR GENERAL AND SCIENTIFIC READERS. tMtOM THE CATALOGUE OF PRESLEY BLAKISTON, Publisher of Medical. Pharmaceutical, Dental, and Scientific Books, 101'i Walnut Street, Philadelphia. t&~ Any of the following books will be sent, postpaid, upon receipt of the price, or they will be found in the stock of most booksellers throughout the United States and Canada. ON SLIGHT AILMENTS. Their Nature and Treatment. By Lionel S. Beale, m.d. Large 12mo. Cloth. Price $1.73. Among civilized nations a perfectly healthy individual seems to be the exception rather than the rule ; almost every one has experienced very fre- quent departures, of one kind or another, from the healthy state ; in most instances these derangements are slight, though perhaps showing very grave symptoms, needing a plain but quick remedy. CONDENSATION OF CONTENTS. The Tongue in Health and Slight Ailments, Appetite, Nausea, Thirst, Hunger, Indigestion, its Nature and Treatment^Dyspepsia, Constipation, and its Treatment, Diarrhoea, Vertigo, Q-iddiness, Biliousness, Sick Head- ache, Neuralgia, Rheumatism, on the Feverish and Inflammatory State, the Changes in Fever and Inflammation, Common Forms of Slight Inflam- mation, Nervousness, Wakefulness, Restlessness, etc., etc. OPINIONS. " It abounds in information and advice, and is written for popular use."— Philadelphia Bulletin. " Singularly clear and felicitous."—Sanitarian. "A valuable work for the family library."—Boston Transcript. " A thoroughly practical work (or non-p-ofessional as well as medical readers."— Cincinnati Gazette. " A scholarly book, singularly free from all technicalities, and.'almost as valuable to general readers as to the profession."— Chicago Inter-Ocean. "Clear, practical, and a valuable instructor and guide."—Baltimore Ga- zette. "The advice given as to treatment is so excellent, that no student or young practitioner should neglect to read it."—Med. and Surgical Reporter. " In a very important sense, a popular book."— Chicago Advance. "An admirable treatise upon the minor ills which [flesh is heir to."— Springfield Republican, 1 2 Presley Blahiston's BRIGHT'S DISEASE. How Persons Threatened or Afflicted with this Disease Ought to Live. By J. F. Edwards, m.d. 16mo, 96 pages. Cloth. Price 76 cents. The author gives, in a readable manner, those Instructions in relation to Hygiene, Clothing, Eating, Bathing, etc., etc., which, when carried out, will prolong the life of those suffering from this disease, and a neglect of which costs annually many lives. WHAT IS SAID OP IT. " Every one should read this excellent little volume, in which Dr. Ed- wards describes and defines the disease."—Providence Journal. " This little book is prepared, not in the interest of the doctor, but of the sufferer."—Louisville Christian Observer. " A very valuable work."—New York Commercial Advertiser. " Plainly written, and ought to be of great use."—Philadelphia Ledger. " "What should be done and avoided are clearly shown, and the informa- tion communicated is of general Interest."—Albany Journal. " Plain and straightforward."—Baltimore Sun. " An admirable and much needed book."—Catholic Mirror, Baltimore. "A remarkably able and useful treatise upon an obscure and vital sub- ject."—North American. "Should be read carefully by every one."—The Voice, Albany, N. Y. "It encourages the sufferer as well as instructs him."—Congregationalist. " An intelligent work."— Toledo Blade. "A clear statement of some of the rules of life, which will insure the longest lease of life, and the greatest measure of health."—Prov. Press. " A satisfactory treatise."—Indianapolis Sentinel. "Of especial interest and importance, and should be universally known." —Lutheran Observer. '' Will be eagerly welcomed by thousands. The malady is one of a pe- culiarly insidious character, and it may be asserted with confidence that this book will be very valuable for medical men as well as lavmen. It is written in good, plain English, and with clearness."—Stoddarfs Review. "Simple, practical directions that can be easily obeyed."— Bookseller and Stationer. " The considerations presented in this little volume are of the greatest moment."—N. E. Journal of Education. "To those for whom it is designed, this manual can hardly fail to be a God-send."—Buffalo Courier. BY THE SAME AUTHOR. JUST BEADY. CONSTIPATION. Plainly Treated and Relieved without tho Use of Drugs. By Joseph F. Edwards, larao. Cloth. Price 75 cents. Select List of Books. 3 THE MANAGEMENT OF CHILDREN in Health and Disease. By Mrs. Amie M. Hale, m.d. A book for Mothers. Second Edition. 12mo. Cloth. Price 60 cents. THE PRESS COMMEND IT AS FOLLOWS I " Altogether, it is a book which ought to be put into every baby basket, even if some lace-trimmed finery is left out, and should certainly stand on evory nursery bureau."—Philadelphia Public Ledger. " Admirable common-sense advice,which mothers would do well to have." —Southern Churchman. ■' Contains invaluable instruction."—Evening' News, Detroit. "The importance of this book cannot be over estimated."—N. E. Journal of Education. " A work for mothers, full of wisdom."—Congregationalist. "Ought to be the means of saving many a young life."—Phila Inquirer. "Abounds in valuable information."— Therapeutic Gazette. " Emphatically a book for mothers, and cannot fail to be useful to all who read it."—Indiana Farmer. " Admirably simple, clear, sensible, and safe in its teachings."—Friends' Review. " It should be upon every household table."—Nashville Jour. Med. and Sur. BIBLE HYGIENE ; or, Health Hints. By a Physician. This book has been written, first, to impart in a popular and condensed form the elements of Hygiene. Second, to show how varied and important are the Health Hints contained in the Bible, and third, to prove that the secondary trendings of modern philosophy run in a parallel direction with the primary light of the Bible. 12mo. Cloth. Price $1.25. NOTICES OF THE PRESS. " The anonymous English author of this volume has written a decidedly readable and wholesome book."—Philadelphia Press. " The scientific treatment of the subject is quite abreast of the present day, and is so clear and free from unnecessary technicalities that readers of all classes may peruse It with satisfaction and advantage."— Edinburgh Medical Journal. DRAINAGE FOR HEALTH; Or, Easy Lessons in Sanitary Science, with numerous Illustrations. By Joseph Wilson, m. d.. Late Medical Director, United States Navy. One vol. Octavo. Price $1.09. " Dr. Wilson is favorably known as one of the leading American writers on hygiene and public health. The book deserves popularity."—Medical and Surgical Reporter. "Easily understood, and briefly and concisely presented."— Providence Journal. " Will be sure to be a harbinger of good in every family whose good for< tune it may be to possess a copy."—Builder and Wood Worker. Presley Blakiston's THE AMERICAN HEALTH PRIMERS. Edited by W. W. Keen, m.d. Bound in Cloth. Price 50 cents each. The Twelve Volumes, in Handsome Cloth Box, $6.00. I. Hearing and How to Keep It. With illustrations. By Chas. H. Burnett, m.d., of Philadelphia, Aurist to the Presby- terian Hospital, etc. II. Long Lire, and How to Reach It. By J. G>. Richardson, m.d., of Philadelphia, Professor of Hygiene in the University of Pennsylvania. III. The Summer and Its Discuses. By James C. Wilson, m.d., of Philadelphia, Lecturer on Physical Diagnosis in Jefferson Medical College. IV. Eyesight, and How to Care for It. With Illustrations. By G-eorge C. Harlan, m.d., of Philadelphia, Surgeon to the Wills (Eye) Hospital. V. The Throat and the Voice. With illustrations. By J. Solis Cohen, m.d., of Philadelphia, Lecturer on Diseases of the Throat in Jefferson Medical College, etc. VI. The Winter and Its Dangers. By Hamilton Osgood, m.d., of Boston, Editorial Staff Boston Medical and Surgical Journal. VII. The Mouth and the Teeth. With illustrations. By J. W. White, m.d., d.d.s., of Philadelphia, Editor of the Dental Cosmos. VIII. Brain Work and Overwork. By H. C. Wood, Jr., m.d., of Philadelphia, Clinical Professor of Nervous Diseases in the University of Pennsylvania, etc. IX. Our Homes. With illustrations. By Henry Hartshorne, m.d., of Philadelphia, formerly Professor of Hygiene in the University of Pennsylvania. X. The Skin in Health and Disease. By L. D. Bulkley, m.d., of New York, Physician to the Skin Department of the Demilt Dispensary and of the New York Hospital. XI. Sea Air and Sea Bathing. By John H. Packard, m.d., of Philadelphia, Surgeon to the Episcopal Hospital. XII. School and Industrial Hygiene. By D. F. Lincoln, m.d., of Boston, Mass., Chairman Department of Health, American Social Science Association. This series of American Health Primers is prepared to diffuse as widely and cheaply as possible, among all classes, a knowledge of the elementary facts of Preventive Medicine, and the bearings and applications of the latest and best researches in every branch of Medical and Hygienic Sci- ence. They are not intended (save incidentally) to assist in curing disease, but to teach people how to take care of themselves, their children, pupils, employes, etc. They are written from an American standpoint, with especial reference to our Climate, Sanitary Legislation and Modes of Life; and in these re- spects we differ materially from other nations. Select List of Books. 5 NOTICES OF THE PRESS. " As each little volume of this series has reached our hands we have found each in turn practical and well-written."—New York School Journal. " Each volume of the 'American Health Primers' The Inter-Ocean has had the pleasure to commend. In their practical teachings, learning, and sound sense, these volumes are worthy of all the compliments they have received. They teach what every man and woman should know, and yet what nine-tenths of the intelligentclass are ignorant of, or at best, have but a smattering knowledge of."— Chicago Inter-Ocean. "The series of American Health Primers deserves hearty commenda- tion. These handbooks of practical snggestion are prepared by men whose professional competence is beyond question, and, for the most part, by those who have made the subject treated the specific study of their lives. Such was the little manual on 'Hearing,' compiled by a well-known aurist, and we now have a companion treatise, in Eyesight and How to Care for It, by Dr. George C. Harlan, surgeon to the Wills Eye Hospital. The author has contrived to make his theme intelligible and even interesting to the young by a judicious avoidance of technical language, and the occasional introduction of historical allusion. His simple and felicitous method of handling a difficult subject is conspicuous in the discussion ■ if the diverse optical defects, both congenital and acquired, and of those injuries and diseases by which the eyesight may be impaired or lost. We are of the opinion that this little work will prove of special utility to parents and all persons intrusted with the care of the eyes."—New York Sun. "The series of American Health Primers (now entirely completed) is presenting a large body of sound advice on various subjects, in a form which is at once attractive and serviceable. The several writers seem to bit the happy mean between the too technical and the too popular. They advise in a general way, without talking in such a manner as to make their readers begin to feel their own pulses, or to tinker their bodies without medical advice."—Sunday-school Times. " Brain Work and Overwork, by Dr. H. C. Wood, Clinical Professor of Nervous Diseases in the University of Pennsylvania, to city people, will prove the most valuable work of the series. It gives, in a condensed and practical form, just that information which is of such vital importance to sedentary men. It treats the whole subject of brain work and overwork, of rest, and recreation, and exercise in a plain and practical way, and yet with the authority of thorough and scientific knowledge. No man who values his health and his working power should fail to supply himself with this valuable little book."— State Gazette, Trenton, N.J. " An unexceptional household library."—Boston Journal of Chemistry. " Every family should have the entire series; and every man, woman, and child should carefully read each book."—Alabama Baptist. WATER ANALYSIS For Sanitary Purposes, With Hints for the Interpretation of Results. By E. Fbankland, ph.d., d.c.l. With Illustrations, Tables, etc , etc. 12mo. Cloth. $1 00. " The name of the author, who is a distinguished Chemist, and has had great experience in Sanitary matters, is a sufficient testimonial to its ac- curacy and its great practical value."— Boston Journal of Chemistry. 6 Presley Blakiston's WHAT TO DO FIRST in Accidents and Poisoning. By Charles W. Dulles, m.d. Illustrated. 18mo. Cloth. Price 50 cents. PREFACE. Whoever has seen how invaluable, in the presence of-an accident, is the man or woman with a cool head, a steady hand, and some knowledge of what is best to be done, will not fail to appreciate the desirability of possess- ing these qualifications. To have them in an emergency one must acquire them before it arises, and it is with the hope of aiding any who wish to prepare themselves for such demands upon their own resources that the following suggestions have been put together. OPINIONS. "Of special practical value, and we commend it to all."— Lutheran Ob- server. " Ought to be in everybody's hands."—Times, Philadelphia. '• Its usefulness entitles it to a wide and permanent circula.ion."—Boston Gazette. "Just the thing for an emergency."—Portland Transcript. " Of great practical value to the public."— Wisconsin State Journal. " A complete guide for sudden emergencies."—Philadelphia Ledger. "So plain and sensible that it ought to be introduced into every female seminary."—Evening Chronicle, Pittsburgh. "The suggestions are of priceless value."—The Traveler, Boston. " The book is invaluable."—Providence Press. EYESIGHT, GOOD AND BAD. The Preservation of'Vision. By Robert Brudenel Carter, m.d., f.r.c.s. With many explanatory illustrations. 12mo. Cloth. Price $1.50. PREFACE. A large portion of the time of every ophthalmic surgeon is occupied, day after day, in repeating to successive patients precepts and injunctions which ought to be universally known and understood. The following pages contain an endeavor to make these precepts and injunctions, and the reasons for them, plainly intelligible to those who are most concerned in their observance. WHAT 18 THOUGHT OF IT. '■ A very valuable book, and should be in everybody's hands."—North American. " A valuable book for all who are interested in the best use and preser- vation of the vision."—A'. E. Journal of Education. " A compact volume, full of information to all classes of people."__Book- seller and Stationer. "A comprehensive treatise, well calculated to educate the public."— Kansas City Review. "Gives excellent advice. "—Chicago Journal. "To teachers particularly the book is of interest and importance."— Educational Weekly. Select List of Books. 7 HEALTH AND HEALTHY HOMES. A Guide to Personal and Domestic Hygiene. By George Wilson, m.a., m.d., Medical Officer of Health. Edited by Jos. G. Richardson, Professor of Hygiene at the University of Pennsylvania. 12mo. Cloth. 314 pp. Price $1.50. WHAT IT TELLS ABOUT. How your Body is Made. The Hereditary Influences, as well as the self-Induced and Social causes of Dis- ease. The Value and Choice of Food, its Preparation, and Sensible Hints on Diet. Proper and well Adapted Clothing. How to take Exercise, and the best Method of Training. Useful Hints about your Home. How to Prevent taking the Infectious Diseases which are always at certain seasons so prevalent in cities. All sorts of Important Suggestions in Regard to the Everyday Life. WHAT IS THOUGHT OF IT. " A most useful and, in every way. acceptable book."— N. York Herald. " Marked throughout by a sound, scientific spirit, and an absence of all hasty generalizations, sweeping assertions, and abuse of statistics in sup- port of the writer's particular views. . . . We cannot speak too highly of a work which we have read with entire satisfaction."—Medical Times and Gazette. " We warmly commend it to the public."— Boston Herald. •' We have read few books of more interest and value than this."— South- ern Practitioner. "The book will take a permanent position. It is a sound work by a com- petent writer."—London Lancet. " Full of good sense and sound advice."—Educational Weekly. "The book aims at the prevention of Disease It abounds in sensible suggestions, and will prove a reliable guide."—Churchman. " Deserves wide and general circulation."—Chicago Tribune. WHAT EVERY MOTHER SHOULD KNOW. Bv Edward Ellis, m.d., Author of a Practical Manual on the Diseases of Children. 16mo. Cloth. Price 75 cents. " As it is only too true that our children have to dodge through the early part of life as through a sort of pathological labyrinth, we must be thank- ful to meet with such a sensible guide for them as Dr. Ellis. He is emi- nently a practitioner among doctors, and a doctor among practitioners; that is to say, he is learned and well knows what is known, can do what should be done, and can put what he has to say in plain and comprehensive language."—Pall Mall Gazette. " The author has a faculty of sketching out the characteristics ] of dis- eases and their treatment in striking outlines, and of making his points very clear and impressive."—N. Y. Medical Record. 8 Presley Blakiston's Select List. DRUGS THAT ENSLAVE. The Opium, Morphine, Hhloral, and Hashisch Habits. By H. H. Kane, m.d., of New York City. ^One volume. 12mo. With Illustrations. Price $1.50. A curse that is daily spreading, that is daily rejoicing in an Increased number of victims, that entangles in its hideous meshes such great men as Coleridge, De Quincey, William Blair, Robert Hall, John Randolph, and William Wilberforce, besides thousands of others whose vice is unknown, should demand a searching and scientific examination. " A vivid and startling expose" of the increase of this form of intemper- ance, and the terrible sufferings endured by those trying to free them- selves from this habit."—Pittsburg Telegraph. " It is well that such a warning as is contained in this book should be sounded."—Albany Evening Journal. " The volume seems to be a summary of the results of the most approved practice, both in Europe and this country."—New York World. " A work of more than ordinary ability and careful research. . . . For the first time, reliable statistics on the use of chloral are classified and published. . . . And it is shown that the use of chloral causes a more complete and rapid ruin of mind and body than either opium or morphine." —Druggists' Circular and Gazette. " The effects of the habits described are set forth boldly and clearly, and the book must have a beneficial effect. It will do still better service in de- terring persons from experimenting 'to see what it is like.'"—Charleston (S. C.) News and Courier. "The subject of the chloral habit has not been investigated by any one, we believe, so thoroughly as by Dr. Kane."—Medical Record. " There is ground for a new temperance movement here. The book is a valuable one. It is written in a practical manner, and has nothing of a sensational character."—Philadelphia Ledger. THE OCEAN AS A HEALTH RESORT. A handbook of Practical Information as to Sea Voyages, for the use of Tourists and Invalids. By Wm. S. Wilson, l.r.c.p.. Lond , m.r.c.s.e. With a Chart showing the Ocean Routes, and Illustrating the Physical Geo- graphy of the Sea. Crown 8vo. Price $2.50. Curative Effects of the Ocean Climate; The Various Health Voyages ; Time of Starting: Choosing a Ship ; Preliminary Arrangements ; Life at Sea; Climate and Weather; Management of the Health at Sea; Occupa- tions and Amusements at Sea; Objects of Interest at Sea; End of the Voyage; Future Plans ; The Homeward Voyage ; Australia—Its Climate, Cities and Health Resorts; South Africa and its Climate; The Meteorol- ogy of the Ocean. Appendix A.—Outfit Required for a Voyage to Austra- lia. Appendix B.—Names and Addresses of some or the Principal Ship- ping Firms. "All the information is supplied by, or based upon, the actual experience of the author; and the book may be confidently recommended to all who have to undertake, without previous experience, a sea voyage of any length. Medical men may consult it with advantage, and commend it to those patients whom they may advise to try the effect of a long voyage at sea."— Med. Times and Gazette. •• We have read every page of this book, and have derived both instruc- tion and amusement."—Lancet. '^^m^^MMvz^^ ">////////■' ■■■ >?o////»/^. 0116016�