A TREATISE 
ON THE 
Diseases of Refraction 
AND 
ACCOMMODATION: 
BY 
C. S. FENNER, M. D., 
LOUISVILLE, KY., 
LATE OF MEMPHIS, TENNESSEE. 
LOUISVILLE, KY.: 
RICHMOND AND LOUISVILLE MEDICAL JOURNAL DRINT. 
1873. A TREATISE 
ON THE 
Diseases of Refraction 
AND 
ACCOMMODATION. 
C. S. FENNER, M. D., 
LOUISVILLE, KY., 
LATE OF MEMPHIS, TENNESSEE. 
LOUISVILLE, KY.: 
RICHMOND AND LOUISVILLE MEDICAL JOURNAL PRINT. 
1873. A TREATISE 
ON THE 
DISEASES OF REFRACTION 
AND 
ACCOMMODATION. 
[From May No. Richmond and Louisville Medical Journal.] 
Within the past few years no department of ophthalmologi- 
cal science has made such rapid progress as that relating to 
the diseases of refraction and accommodation. 
I propose in this paper to give a brief account of the views 
on these subjects at present entertained, and of the most ap- 
proved means of remedying them. Many cases of amblyopia, 
that a few years since would have been considered as incurable, 
are now entirely relieved by neutralizing the aberrations of re- 
fraction by appropriate lenses. It is definitely settled, that 
the inherent power possessed by the eye of adapting itself to 
see an object clearly and distinctly at different distances, is 
due to the voluntary action of the ciliary muscle on the crys- 4 
REFRACTION AND ACCOMMODATION. 
talline lens; causing the latter to change its curvatures as the 
object approaches or recedes from the eye, so that, within cer- 
tain limits, diverging rays coming from it are united in a focus 
on the retina. It was formerly supposed that both the iris 
and the external muscles of the eye-ball assisted in accom- 
modation, but it has been found that in congenital absence 
of the iris, and in one instance of its accidental removal, 
the accommodation has been normal. I have myself met 
with a case of paralysis of the external muscles of the eye in 
which the accommodation remained perfect. If we take a 
small object (No. 1 Snellen) and hold it at the farthest distance 
at which the normal eye can distinctly and sharply see it, we 
have the far point (r), and this represents the natural refrac- 
tive state of the dioptric apparatus. If we now bring the ob- 
ject to the nearest point at which it can be seen with equal clear- 
ness, we have the near point (_p). The distance of each point 
from the eye is represented, respectively, by P and P. The dis- 
tance between the far and near points is the range of accom- 
modation (A), and the measure of any point on that line for 
which the eye may be accommodated, is the amount of adjust- 
ment. Practically, rays of light emanating from the far point 
of the normal eye are regarded as parallel, and as coding from 
an infinite distance (oo). The range of accommodation is 
found by the following formula : A = p — r. If the far point 
is 12"* (infinite distance), and the near point 4", then A = J— 
oo = Hence A represents a convex lens of 4" focus, and 
the ciliary muscle has the power of changing the curvatures of 
the lens so as to add to it a power equal to a lens of 4". The 
smallest angle at which the emmetropic eye can ordinarily see 
with distinctness, is one of five minutes, hence this has been 
adopted as the normal angle. Snellen has devised test types, 
each one representing an angle of five minutes, and numbered 
according to the number of feet they are to be held from the 
eye. If one can, without the assistance of the accommodation, 
* The reader will observe that these symbols represent (/) foot, (//) inch, and 
line. REFRACTION AND ACCOMMODATION. 
5 
read No. 1 at 1', and No. 20 at 20', he has normal vision, and 
his eyes are emmetropic (V = 1). Some eyes can see at a 
smaller angle than five minutes. If No. 20 can be read at 30' 
and No. 1 at 18 ", then the sharpness of vision is greater than 
normal, and is expressed by V = or If No. 20 can only 
be read at 10', then V = 2°, and the sharpness of vision is di- 
minished one-half. 
When the natural refractive state of the dioptric apparatus 
falls too low to unite parallel rays in a focus on the bacillar 
layer, but is adjusted for virtual images behind the retina, the 
eye is said to be hypermetropic, and, unless assisted by the 
accommodation, sees objects indistinctly. When in the emme- 
tropic eye the near point recedes beyond 8", it is said to 
be presbyopic. The convexity of the cornea often varies in its 
different meridians. When this is the case, planes of homo- 
centric light falling on the different meridians are not united 
at the same point, but those falling on the most convex 
meridian are united first, and those upon the meridian least 
convex last. This is astigmatism of the cornea. If similar 
inequalities exist in the lens, it produces lenticular astigma- 
tism. The ocular axis and visual axis are not the same. The 
former corresponds with the long axis of the cornea, and is 
represented by a line drawn from its vertex through the poste- 
rior schleral pole—wdiich is about midway between the external 
edge of the optic disk and the yellow spot. The latter—that 
is, the axis of the vision or optic axis—corresponds with the 
axis of the lens, and is represented by the visual line, which 
passes from the yellow spot—the point of direct vision— 
through the nodal point—the optical centre of the eye—to the 
point of fixation, usually cuts the cornea inside of its zenith, 
and slightly below its horizontal meridian. The horizontal devi- 
ation in the normal eye varies from two to three degrees ; in 
the hypermetropic eye from three to nine degrees, while in the 
high grades of myopia, the visual line may cut the cornea out- 
side of its zeninth. These variations in the visual lines have a 
marked influence upon the degree of convergence necessary in 6 
REFKACTION AND ACCOMMODATION. 
the different abnormal conditions of the eyes, and often give 
rise to an apparent squint. When a small object is slowly 
moved towards the eyes, the ciliary, the internal recti, and the 
circular muscles of the iris gradually contract, until the near 
point is reached; then the two former muscles are in a maxi- 
mum state of tension; as the object recedes, these relax until it 
reaches the far point, when the ciliary and internal recti muscles 
are in a minimum state of contraction. 
There is in binocular vision an intimate association between 
accommodation and convergence. With a certain amount of 
accommodation we have a certain amount of convergence, and, 
vice versa, with a certain amount of convergence there is a cor- 
responding amount of accommodation; but these relations are 
not absolute; for, with the same convergence, an object may be 
brought a little nearer, or receded from the eye, without inter- 
fering with the sharpness of vision. The difference is relative 
accommodation. Then again, with a certain amount of ac- 
commodation the convergence may be slightly increased or 
diminished without disturbing vision. This variation represents 
relative convergence. For easy vision, relative convergence 
and relative accommodation must bear a certain proportion to 
each other, and these relations cannot long be disturbed without 
inducing retino-ciliary hypersemia and its attendant symptoms. 
In relative accommodation—that is, the maximum variation 
that can take place with a certain convergence—that part in- 
duced by relaxation of the ciliary muscle is negative, while 
that caused by an increased muscular tension is positive. The 
positive must bear to the negative a relation of about three to 
two.—\_Loring.] 
These relative associations only represent possible condi- 
tions, they cannot be maintained for any considerable length 
of time. They act in equalizing the adjustment, very much 
like a spring in a machine equalizes force when suddenly 
applied. In quick and successive changes of the distance of 
small objects looked at, they temporarily preserve uninter- 
rupted vision while the convergence and accommodation are MYOPIA. 
7 
becoming accurately adjusted. To the surgeon a thorough 
knowledge of the intimate associations existing between accom- 
modation and convergence is of the utmost importance; for 
upon it will in a great measure depend his success in treating 
many of the diseases of the eye. 
In order to thoroughly comprehend the anomalies of refrac- 
tion and accommodation, it is requisite for the surgeon to make 
his own eye myopic, hypermetropic, or astigmatic, by suitable 
lenses, and then study the etfect produced; after which he 
should select such glasses as neutralize the artificial anom- 
alies, and restore normal vision. He can then more readily 
understand and appreciate the symptoms described by patients, 
and, as a matter of course, be better qualified to diagnosticate 
and treat these diseases. 
MYOPIA. 
Myopia consists in a diminution of the distance of the far 
point, and when the accommodation remains normal, of a cor- 
responding change in the near point. The eye is too long in 
its antero-posterior diameter, or its refractive power is so high 
that parallel rays are united too soon; they cross and meet the 
retina in circles of dispersion. For distinct vision, objects re- 
quire to approach the eye in proportion to the grade of the 
myopia, so that rays of light emanating from them may meet 
the cornea as divergently as may be necessary to form the re- 
quired image on the bacillar layer of the retina. The grade of 
the myopia is said to be low when the far point is beyond 14"; 
medium when it is between 6" and 14"; and high when it does 
not reach 6". In the latter case the near point is sometimes 
less than 2" from the eye. To find the far point, it is usual to 
take moderately fine print (No. 4 Jseger), and hold it as far 
from the eye as it can easily be read. The distance noted 
represents the far point, the grade of the myopia, and the focus 
of a negative glass necessary to neutralize it. If the far point 
is found to be twelve inches, then with a concave lens of 12" 
focus the patient should be able to read No. 20 Snellen at 20'. 8 
MYOPIA. 
In low and medium grades of myopia the sharpness of sight 
within the clear visual distance is just as great as in the emme- 
tropic eye, and owing to the increased size of the visual angle, 
the myope can do fine work by a weaker illumination, and con- 
tinue at it longer without fatigue. It was formerly thought 
that myopia was caused by too great a convexity of the cornea, 
but the ophthalmometer shows that it is usually less convex 
than in the emmetropic eye; still a conical cornea may 
render the eye myopic. The crystalline lens may have an ex- 
cessive convexity naturally, but rarely enough so to cause any 
other than a low grade of short-sightedness. Long-continued 
work on objects requiring great accommodation may induce an 
excessive development of the ciliary muscle, with increased 
tonicity, so that it cannot readily relax and allow the lens to 
be adjusted for the normal far point (plesiopia). 
Perhaps in these cases the crystalline capsule—the chief op- 
posing power of the ciliary muscle—loses some of its elasticity, 
and does not contract sufficiently to give the lens the dimin- 
ished degree of convexity necessary to the adjustment of the 
eye for the normal far point, when the tension of the muscle is 
reduced to its minimum. 
Myopes are in the habit of partially closing their lids, in order 
to shut out the circumferential rays that greatly increase the 
circles of dispersion, and are thus enabled to get a better view 
of objects situated beyond the far point; hence they are some- 
times called “blink-eyed.” Myopia may be congenital, and is 
often hereditary; the most frequent cause is an excessive poste- 
rior development of the eye in the direction of its optic axis 
during the growth of the body in childhood (bathymorphio). 
Another cause is posterior staphyloma; this frequently attacks 
bathymorphitous eyes, and increases the abnormal state already 
developed, or it may occur in emmetropic eyes during any pe- 
riod of life, and is always the cause of high grades of myopia 
that develop after the eye has attained its normal growth. The 
elongation of the eye-ball in the direction of its optic axis 
causes it to be very prominent, to force the lids wide apart, and MYOPIA. 
9 
to protrude more or less from the orbit; and when turned far 
inwards, the squarely ovoid shape caused by the pressure of 
the recti muscles can be plainly seen. The point of rotation 
of the eye is relatively moved forward on the elongated visual 
axis; consequently to produce different degrees of convergence, 
greater motion is necessary, requiring increased muscular con- 
tractions. 
The ophthalmoscope may be used to find the far point; an 
inverted vertical image is formed very near the cornea, which 
the observer can see with the concave mirror by placing his 
eye at a proper distance. If the examiner knows the adjust- 
ment of his own eye, then find its distance from that of the 
patient’s, subtract the distance of his own adjustment, and 
the result will give the far point of the eye of the pa- 
tient. Children affected with myopia should exercise great 
care, and avoid reading or writing in dimly-lighted apart- 
ments. They should sit so as not to face the light, but to 
allow a clear, direct illumination to fall on the book. At school, 
desks should not be so low as to require the bending of the 
neck and body. Reading in a recumbent position should be 
avoided, and if at any time the eyes feel fatigued, the use 
of them for near vision should be at once suspended; for 
nothing tends more to the development of bathymorphia and 
posterior staphyloma than vascular excitement induced by ex- 
cessive use of the eyes. By the exercise of great care, and by 
proper prophylactic measures, an increase of the abnormal 
elongation may be prevented; but a restoration of the eye to its 
normal condition cannot be expected: for distant vision, re- 
course must be had to a lens with a negative focus of sufficient 
power to render parallel rays as divergent as may be necessary 
to make the proper retinal image. The farthest distance at 
which the patient can read moderately-sized print, gives us his 
far point, and its distance from the eye, measured from the 
nodal point, gives the focus, theoretically, of the lens required 
to neutralize the myopia. If the far point be 12", then a lens of 
— 12 inches focus would be the proper one to> make his Y—1 10 
MYOPIA. 
that is, to see at an infinite distance—No. 20 Snellen, at 20.'* 
Practically, a concave glass of 12 inches focus is found to be 
a little too strong; for the convergence of the visual axes at 
12" prevents the eyes from accommodating themselves for the 
normal far point; hence we should by means of trial lenses se- 
lect those that are exactly adapted to his case, and render vision 
most easy and distinct. 
In short-sightedness of medium and high degrees there is 
frequently a deficiency of relative accommodation, so that 
should the error of refraction at once be entirely neutralized, it 
would give rise to muscular asthenopia; hence it is better to 
begin with weaker glasses, and increase them from time to 
time for those of higher power, until the proper ones can be 
worn. This course allows the natural relations existing be- 
tween accommodation and convergence gradually to become 
accustomed to the changed conditions of association. 
Myopia of very high grade cannot be entirely neutralized; 
■owing to the distance of the glass from the eye, the image is so 
reduced in size that the object has to approach very near the 
■cornea, in order to attain the necessary visual angle. In me* 
■dium and high grades of the disease, the same glass will not an- 
swer for near and distant vision; for it is necessary that the 
ray of direction should pass through or near the centre of the 
lens. If the spectacles are adjusted to see at a distance—then 
for near vision, owing to the great convergence of the visual 
axes,—the light lines would pass through the glasses at a con- 
siderable distance from their centres, which would bend them 
the same as prisms with curved surfaces; consequently, for near 
vision the centre of the glasses should be made to approach each 
* In the calculations for the adjustment of spectacles, I have neglected to 
take into consideration the distance of the glass from the eye. This is unne- 
cessary, unless the required-glasses are of very high power. If, for instance 
in myopia, the far point be 6", and the glass is half an inch from the eye, 
then its focus should be 5J inches; on the contrary, in high grades of hyper- 
metropia the focal length of the required glass should be increased by its dis- 
tance from the eyes. HYPERMETROPIA. 
11 
other, so as to correspond to the visual l«n1f from the point of 
fixation. 
For binocular near vision in high grades of myopia—owing 
to the visual axis frequently cutting the cornea outside of its 
zeninth, and to the antero-posterior elongation of the eye-ball,— 
ft requires excessive exertion of the internal recti muscles to 
converge the visual axes to the point of fixation. If the dis- 
ease has been slowly developed, often these muscles attain ab- 
normal strength and development, so as to be capable of sus- 
taining, for a long time, a great degree of tension, but usually 
after a while the muscles tire; one of them fails, and the eye 
turns outward. After a short period of rest this muscle regains 
its power, but if used too soon speedily becomes fatigued again, 
and we have muscular asthenopia. This becomes so trouble- 
some that patients often give up binocular vision, and turn the 
eye not used outward, so that rays of light from the object may 
strike a part of the retina least sensitive, and cause less disturb- 
ance to the retinal image of the other eye. The patient learns 
to suppress the image of the unused eye, which, from want of 
use, soon in a great measure loses its sharpness of vision (ances- 
thesia optica or amblyopia ex anapasia). Most of the cases of 
divergent strabismus arise from this cause. 
HYPERMETROPIA. 
Here the far point is removed from positive infinity to a 
negative distance. The reverse occurs from what we find in 
myopia; the refractive power of the dioptric media is too low, 
or the eye is too short in the diameter of its optic axis, so that 
parallel rays meet the retina before they are united in a focus, 
and objects are seen in circles of dispersion. Hypermetropia 
is divided into facultative, relative, and absolute. In the former 
the far point is behind, and the near point in front of the retina. 
A part of the accommodation is necessary for distinct vision of 
distant objects. The near point may recede until it becomes 
the normal far point; then the entire power of accommodation 
is exhausted; slightly beyond this, vision may be rendered pos- 12 
HYPERMETRCPIA. 
itive by giving up binocular vision and converging the optic 
axes to a point nearer than the one of binocular fixation {rela- 
tive hypermetropia); for when the accommodation remains normal 
the near point may be brought nearer, and the far point receded 
by the convergence or divergence of the optic axes. When the 
eye fails to unite parallel rays on the retina by the aid both of 
the accommodation and excessive convergence, it is absolutely 
hypermetropic—the clear visual distance is entirely negative. 
Children and young persons with hypermetropia, when they 
are required to read, write, or perform other occupations de- 
manding near and sharp vision, soon learn by experience 
the increase of power of accommodation gained by excessive 
convergence of the visual axes. A part of their accommo- 
dation being used for distant vision, for the near point, it 
requires the maximum tension of the ciliary muscle, which 
soon tires, and the object becomes indistinct; then the child 
finds that by squinting inward he can restore the sharpness 
of sight with less strain of the accommodation. At first 
the squint is periodic, the eyes becoming parallel as soon as 
they are removed from the object, but speedily returns if 
near vision is resumed, and the squint eventually becomes per- 
manent. It is said that seventy-five per cent, of the cases of 
convergent strabismus arise from this cause. The hyperme- 
trope frequently learns to read very fine print by holding it an 
inch or two from the eye; he attains wonderful facility in this 
respect, and is often thought to be very near-sighted. The 
visual angle increases in an inverse proportion to the distance 
of the object; hence, it becomes very large when the print is 
held near the eye. By contracting the pupil and partially 
closing the lids, so as to shut out as much as possible the cir- 
cumferential rays, the circles of dispersion are largely dimin- 
ished ; then by a forced uniform contraction of the recti muscles 
the print becomes clear and distinct. 
I believe that the strong contraction of these muscles, at- 
tached, as they are, anteriorly near the margin of the cornea 
and posteriorly around the optic foramen, with their broad bel- HYPERMETROPIA. 
13 
lies resting on the equator of the partially yielding eye-ball, 
lessens its transverse diameter and slightly increases its 
length in the direction of its optic axis. The lessening of its 
transverse diameter exerts a direct pressure on the equator of 
the lens, and renders it more convex than it can be made by 
the maximum tension of the ciliary muscle. This accounts for 
the increased accommodation caused by convergent squint; 
here the excessive action of the internal rectus requires an in- 
creased tension of the other recti muscles, in order to steady the 
eye. A greater lateral pressure is the result, which extends 
to the equator of the lens. One can easily prove this by 
trying the experiment on his own eye. Take No. 1 Jaeger, and 
hold it one and a half inches from the cornea; let the book and 
the eye be well illuminated, contract the pupil, partially close 
the lids, and exert the full power of the ciliary muscle; the 
print is seen in circles of dispersion; now forcibly contract the 
recti muscles, and instantly it will become very black, sharply 
defined, and twice or thrice its natural size. 
Hypermetropia may be hereditary, and is often congenital, 
but the most frequent causes are senile involutions in the eye 
with advancing age, and in children the arrest of the growth 
of the sclerotica in the direction of its optic axis, making the 
eye too flat (pathy morphia), which is also small and deeply set 
in a shallow orbit, giving the face a peculiar flattened appear- 
ance. In young persons the disease is often masked; a portion 
of the power of accommodation being exhausted in adjusting 
the eye for parallel rays, the ciliary muscle, by unusual strength 
and activity, may bring the near point to its normal distance, 
so that V still equals 1. 
The hypermetropia may be detected by placing before the eye 
of the patient the strongest convex glass with which he can 
read No. 20 Snellen at 20'; but this does not give the real 
grade, because he cannot completely relax the muscle of accom- 
modation. Hence it must be paralyzed by the repeated instil- 
lations of atropia; then the number of the lens required to read 
No. 20 Snellen gives the grade of the disease. In well marked 14 
PRESBYOPIA. 
plathymorphitous eyes, and in hypermetropia of high grade, 
the sharpness of vision is always diminished, and cannot be 
entirely restored by the use of convex glasses. Here, as in my- 
opia, children should exercise great care, and avoid straining 
their eyes by reading, writing, or doing fine work by an insuf- 
ficient illumination. Convex glasses should be selected that 
just neutralizes the latent hypermetropia; these are to be used 
for near vision only, and should enable the facultative hyper- 
metrope to accommodate for the near point with the same ease, 
and continue to do so as long as those with emmetropic 
eyes, and prevents the development of convergent squint. In 
absolute hypermetropia, theoretically, different convex glasses 
are required for every change in the distance of the object, but 
in practice two pairs of spectacles will ordinarily suffice; one 
pair should be selected that enables the patient to distinctly see 
No. 20 Snellen at 20'. Then another pair of sufficiently high 
power to make No. 1 easily read at from 8 to 10 inches. 
PRESBYOPIA. 
Presbyopia is simply a recession of the near point with ad- 
vancing age, and consequently, sooner or later, affects all per- 
sons. The near point gradually recedes from childhood, but it 
is not usually noticed until about the age of forty or forty-five 
years, when, in reading or looking at small objects by artificial 
light, or by day in dimly-illuminated apartments, vision be- 
comes indistinct, and the object has to be removed to a consid- 
erable distance from the eyes; this reduces the size of the 
visual angle to such an extent that the eyes soon tire, become 
painful, and the reading has to be suspended. By increasing 
the light, easy vision is at once restored. This is because a 
stronger light contracts the pupil and shuts out the circumfer- 
ential rays that meet the retina in circles of dispersion. Soon 
the near point becomes so distant that in the most favorable 
illumination small objects, as print, for instance, cannot be 
sharply seen—the letters are blurred and indistinct. Accord- 
ing to Bonders, presbyopia commences when the near point has PRESBYOPIA. 
15 
receded beyond 8", and this rule has been generally adopted. 
I am satisfied that in this country, particularly in the South 
and West, the normal visual angle is less than five minutes. 
From a large number of tests, I have found that most per- 
sons have clear and sharp sight with a visual angle of four min- 
utes. In Germany, and some other European countries, the 
inhabitants are proverbially short-sighted. An angle of five 
minutes is the smallest one (except in small children) at which 
they can ordinarily see with distinctness. For generations a 
large proportion of the population have been accustomed 19 
work in doors, frequently in manufactories, requiring constant 
strain of accommodation. Those who receive a liberal educa- 
tion are unusually studious, often spending for years twelve or 
fifteen hours daily in reading, writing, etc. These habits long 
continued have had a marked influence on the formation of 
their eyes, gradually diminishing the distance of the far point. 
Here we have exactly the reverse; the people have, as a rule, 
been reared in the rural districts; as children, they have 
roamed over our hills and prairies, and by their amusements 
and occupations, have cultivated sharpness of sight for distant 
objects. They rarely spend much time in close study, or learn 
trades requiring constant exercise of the accommodation, such 
as engraving, watch-making, etc.; nor have we manufactories 
that demand an unusual amount of sharp vision for minute ob- 
jects. The result is that, as a people, we are far-sighted. It is 
rare to find one here, under thirty-five years of age, who can- 
not easily read No. 1 Snellen at 20", and No. 20 at 30', 
(V = » *>), far more exceeding this than falling short of it. 
Under thirty, I find the near point from 5" to 6", evidently 
more distant than it is, as a rule, in Germany. These views 
being established, I think that with us 8" is too near for the 
starting point of presbyopia. 
I have for some years in my practice made it 10", with the 
most marked favorable results in preventing the rapid increase 
of senile changes, and preserving the sight with but compara- 
tively slight impairment to advanced age. If the recession of 16 
PKESBYOPIA. 
the near point beyond 8" is taken for the commencement of 
presbyopia, then when it has become 12", to bring it back to 
8", it requires a lens of 24" focus, for g — 12 = 24; whereas, to 
bring it to 10", it would require a glass of 60" focus, for 
jo —12= 60- Owing to the power of accommodation gained by 
the convergence of the optic axes, these numbers would be a 
little too strong, and 30 and 7l2 would, in practice, be found to 
answer the required purpose. 
In all theoretical calculations, the eye is considered simply as 
a dioptric apparatus; to render these results practical, the as- 
sociations existing between the ciliary and internal recti mus- 
cles must be taken into consideration. Glasses that would, the- 
oretically, neutralize the errors of refraction, are usually too 
strong; “ they compel the muscle of accommodation to a relax- 
ation greater than corresponds to the developed circumstances 
of association.” Surgeons often forget this important consid- 
eration (and opticians who adopt most of the spectacles are 
generally ignorant of it, as they are of the theory of re- 
fraction and accommodation), and recommend glasses that are 
too strong, and consequently absolutely injurious. Every oph- 
thalmic surgeon should have a complete set of trial lenses, 
with numbers ranging at least from 2 to 72 (and I would pre- 
fer to 96), and by actual tests find the number that will ena- 
ble‘the patient easily, and for a long time, to read moderately 
fine print held from 12" to 14" from the eyes. 
The habitual use of glasses too strong in the commencement 
of presbyopia is a most powerful factor in inducing rapid senile 
changes in the lens and muscles of accommodation. The ciliary 
muscles are relaxed, and only required to contract to a certain 
point; they soon become enfeebled, and lose the power to act 
beyond their accustomed tension; this state of tension soon in- 
dicates their maximum strength, which cannot long be main- 
tained; hence, lenses of higher power must be substituted to 
relieve the strained accommodation. 
Now, this substitution of convex lenses for accommodation 
from muscular power has a direct influence in increasing the PRESBYOPIA. 
17 
firmness and solidity of the crystalline lens. The latter is of a 
jelly-like consistency, that is, constantly changing its shape as 
it is acted upon by opposing forces. In children it is quite 
soft and supple, but its firmness increases with advancing 
age, so as to require additional force to produce the same 
amount of change in its curvatures; the necessity for these 
changes are lessened just in proportion to the strength of glasses 
used; consequently, as the motion of its particles on each 
other are proportionally diminished, these lose their suppleness, 
become firm, and offer increased resistance to the already 
enfeebled accommodation. The result is, that strong glasses 
weaken the muscle of accommodation by diminishing the ne- 
cessity for its action; this produces an increased firmness of the 
lens by lessening the motion of its particles on each other, and 
this in its turn reacts on the muscle, by demanding increased 
action from its already weakened fibers. 
Both of these factors, acting and reacting on each other, 
causes a rapid increase of the presbyopia and the early com- 
mencement of hypermetropia. Now the question arises, What 
is ordinarily the proper focus of convex glasses suited to one 
who first notices difficulty in seeing distinctly in dimly-lighted 
apartments? I have already stated that I have found No. 72 
answer all the required indications and give perfect satisfac- 
tion. 
In reading a work by Sichel, published at Paris in 1848, en- 
titled “ Spectacles, their Uses and Abuses,” I became strongly 
impressed with the practical views he advocated in regard 
to the use of the low numbers of glasses in commencing pres- 
byopia. He says, ‘‘'Generally speaking, opticians commence 
with too powerful numbers, and augment too rapidly their refrac- 
tive force. Ten years ago they nearly always took No. 48 as 
their starting point, and patients were soon forced to descend 
to Nos. 30 and 24. The result was, that it was common to see 
persons between the age of fifty and sixty years making use 
of glasses between Nos. 12 and 8, and complaining, as we shall 
soon explain, that even then they saw but dimly, and that their 18 
PRESBYOPIA. 
sight declined from day to day. . . . From the results of 
my observations I have taken No. 72 as a point of departure; 
which number, in general, is suitable for those who have not 
yet begun to use spectacles, and who assume them at the 
opportune moment, that is, at the age of forty or a little later. 
Often, however, especially for those below forty, Nos. 80 and 
96 are entirely sufficient during a long time. At first the opti- 
cians of Paris deemed the use of too feeble glasses singular, 
and even ridiculous, regarding them as almost without force. 
. . . Little by little, they have seen this practice sanctioned 
by its results. . . . The method of beginning by the high- 
est numbers has now7 been generally adopted, and I see persons 
every day to whom the opticians have recommended the use of 
convex glasses No. 72, and who have been perfectly satisfied 
with those during several years. It is an error to assert that 
it is absolutely necessary to change them (the spectacles) from 
time to time. On the contrary, it is best to change them as 
rarely as possible; and not at all, if a necessity for doing so is 
not felt. It is only through commencing by too powerful 
numbers, and neglecting hygienic rules, that the necessity is 
created for changing soon and often.” 
For some years I have acted on the views so forcibly ex- 
pressed by M. Sichel, with results so favorable, that I wish 
every ophthalmic surgeon and optician would give them a trial. 
While penning these lines a gentleman fifty years of age called 
at my office, who has for several years been using glasses No. 
72, and can read with them, by good light, for hours without 
experiencing the slightest fatigue. For night-reading, or by 
artificial illumination, he now wears No. 60, but he never puts 
them on in the day-time, unless in a badly-lighted room. I 
tested his eyes, and found that he read with his left eye No. 1 
Jmger at 12", with his right at 15"; by the aid of glasses No. 
72, he read with left eye at 8', with right at 12." 
His eyes up to the commencement of presbyopia had always 
been emmetropic. I know many persons past the age of 
forty-five years who, acting upon my advice, wear glasses No. PRESBYOPIA. 
19 
72, and have not felt any necessity for an increase of their power. 
•I was recently consulted by a gentleman about sixty years 
of age, who requested me to select for him appropriate glasses; 
his sight had failed so that he had difficulty in reading. I 
found that he began the use of glasses that magnified consider- 
ably, and had frequently changed them for those of still higher 
power, until he was at that time using No. 7 for near vision, and 
No. 16 for seeing at a distance. On testing his eyes with trial 
glasses, I found that he saw better at a distance with No. 18 
than with No. 16, thus showing that he had even gone be- 
yond actual necessity in increasing the strength of his glasses, 
and his eyes were suffering in consequence. 
In making trials for the selection of proper spectacles, the pa- 
tient should always begin with those that are a little too weak, 
and increase the numbers until he finds a pair that makes the 
letters .at 12", or 14", look clear, distinct, sharply defined, and 
of the natural size—as near as possible as they looked before 
his eyes were presbyopic. If he makes trial at first of those 
that magnify too much, it interferes with his judgment; the 
objects look unnaturally large, bright, and distinct; when the 
really proper glasses are found, he compares the impression 
they produce with those of the stronger ones, and is dissatis- 
fied with them. 
Empirics often take advantage of this, and select strong glasses 
for their patrons, who, finding that objects appear unnaturally 
clear and bright, imagine that it is owing to some peculiar 
quality in the material, or to the manner in which the lenses 
are made, and are ready to testify to the wonderful skill of the 
maker or vender. After a few weeks’ use, however, they find 
the eyes become painful, sensitive to light, inflamed, and the 
glasses have to be laid aside. In the meantime, the vender has 
sought other fields to dispose of, at fabulous prices, his “ marvel- 
ous spectacles.” 
Many are prejudiced against glasses, and decline to wear 
them when their use is imperatively demanded. This is wrong; 
in attempting to look at small objects, they strain the accom- 20 
ASTIGMATISM. 
modation by requiring it to act beyond its strength. The re- 
sult is accommodative asthenopia, which, if not promptly re- 
lieved by giving up near vision, or by wearing appropriate 
glasses, terminates in hypermmia of the retina, ciliary neural- 
gia, redness of the conjunctiva, and which, if allowed to con- 
tinue long, may end in incurable amblyopia. To preserve the 
sight unimpaired the longest possible time, it is requisite, as 
soon as it begins to fail, to select the weakest glasses that will 
make vision easy; and as the failure at first is barely percepti- 
ble, very slight assistance is needed, and spectacles, Nos. 84 or 
72, are all that is required.* On first adjusting the eye for 
reading, should the print seem a little indistinct if it is carried 
off at arm’s length and then brought near the eye, and this re- 
peated three or four times, then at the normal distance the print 
can be easily read without fatigue. This action accounts for 
the temporary increase in the power of the eye to adjust itself 
for the near point, sometimes seen after the use of the so-called 
"eye cups” and “sight restorers,” so extensively advertised by 
empirics, the action of which is to lessen the transverse diame- 
ter of the eye-ball, and thus by pressure on the equator of the 
lens, forcibly to loosen the particles of the latter, which have 
been rendered too firm by senile changes. The lens is thus 
temporarily made softer and more supple, so that it opposes less 
resistance to the action of the ciliary muscle. 
ASTIGMATISM. 
The cornea is not a section of an ellipse rotated, but of one 
with three diameters, the shortest of which is vertical, the next 
horizontal. This makes the vertical meridian more convex 
than the horizontal. The maximum and minimum curvatures 
* It is difficult to procure low numbers of spectacles outside of metropolitan 
cities. Few opticians can be prevailed on to keep them. They may be ob- 
tained up to 72-inch focus from Jas. W. Queen & Co., No. 924 Chestnut street, 
Philadelphia, and will be forwarded by mail on application to them. Of 
course, if opticians will generally keep low numbers, there will he no necessity 
for ordering them from a distance. ASTIGMATISM. 
21 
are usually perpendicular to each other, and both are perpen- 
dicular to the long axis of the cornea. The crystalline lens 
also varies in its different meridians, but the maximum curva- 
ture is usually horizontal, and the minimum vertical, so that 
the lens partially neutralizes the astigmatism of the cornea. 
For the better understanding of the irregular refractions 
causing astigmatism, it is well to describe the effect on two 
planes of homocentric light from a bundle of rays passing 
through a small round hole in a window-shutter in the direc- 
tion of the prolonged optic axis; one plane passing through the 
meridian of the maximum, the other through that of the mini- 
mum curvature. If a thin metal plate with two narrow slits cut 
in it, crossing and standing perpendicular to each other, is placed 
before the eyes, so that one slit shall correspond to each of the 
principal meridians of the cornea, it will permit two planes of the 
homocentric bundle of rays to pass into the eye. The vertical 
plane, passing through the maximum curvature of the cornea, 
will first meet at a point. If we imagine a shade held at this place, 
the horizontal rays not yet having united will form a horizon- 
tal line on the shade. A little further back the still converging 
rays will be crossed by rays of the vertical plane, which has 
already met and are now diverging; at a certain place these 
lines will be of equal length. Still further back the horizon- 
tal rays meet in a point, and the vertical ones form a vertical 
line on the shade a little longer than the anterior horizontal 
one. The former is called the anterior focal line, the latter the 
posterior. A line drawn through the points of meeting of the 
two planes of light represents the focal tract. The point of 
crossing of the two lines of equal length is a little anterior to 
the middle of this line, and is called the middle focus. We 
will now remove the plate from before the eye, and allow the 
entire bundle of rays to fall on the cornea, and trace the changes 
produced on them. 
If we imagine the shade to be held in front of the anterior 
focal line, the bright spot will be of an oval shape with its long 
diameter horizontal; as the shade moves backward, its eccen- 22 
ASTIGMATISM. 
tricity will increase until at the point of union of the rays of the 
vertical plane, it will be drawn out into a horizontal line; passing 
backward, it again becomes oval, but the eccentricity decreases, 
until at the middle focus, it will be nearly circular; after which 
it again becomes oval with long diameter vertical; its eccen- 
tricity increases until at the point of meeting of the rays of the 
horizontal plane, the crossed rays form a vertical line. Passing 
the shade still backward, the bright spot again becomes oval 
with long axis vertical. 
At the middle focus, where the image appears circular, two 
planes of light, meet, each passing through meridians of the 
cornea at angles equally distant from the vertical and horizon- 
tal meridians; here is the greatest concentration of rays with 
the smallest disturbance from circles of dispersion; conse- 
quently, if the eye can be so adjusted as to bring this focus on 
the retina, it gives the most distinct vision. 
Nearly all eyes are astigmatic, but not enough so to disturb 
the sharpness of vision. This is called normal regular astig- 
matism. By looking through a stenopaic slit, vertical lines 
are seen at a greater, and horizontal lines at a shorter distance. 
When the difference in the refractions of the several me- 
ridians is so great that vision is disturbed, it is called abnor- 
mal regular astigmatism. To detect this, various means have 
been employed. Graefe invented an optometer, composed of 
fine wires crossing each other at right angles. At a certain 
distance, corresponding to the focal point of one of the principal 
meridians, one set of wires are seen, while the others crossing 
them are indistinct or not seen at all. Another method is by 
making numbers of groups of three lines, parallel to each 
other, diverge from a point like the spokes of a wheel. If this 
figure is moved away from the astigmatic eye when it arrives 
at a certain point, only those groups will be distinctly seen that 
correspond to the meridian of a certain curvature of the cor- 
nea. If the figure be moved further off, or the accommodation 
be changed, other groups of lines will become very black and 
sharply defined, while those first seen are pale and indistinct. ASTIGMATISM. 
23 
By looking through a slit in a stenopaic instrument, or 
through a narrow slit cut in a thin blackened metal plate at a 
round or square object of sufficient size to give parallel rays at 
20' distant, and placing behind the slit a convex or concave 
glass that renders the object most distinct, the focal length of the 
glass required gives the grade of the myopia or hypermetropia 
of that meridian. If the head is erect, each of the two princi- 
pal meridians can easily be found; they usually stand perpen- 
dicular to each other, and correspond with the vertical and hori- 
zontal meridians of the cornea. 
Another very satisfactory test for astigmatism, is by means 
of a hole half a line in diameter, made in the window-shutter 
of a darkened room, or a small round hole in a blackened metal 
cylinder placed over a lamp. If there be abnormal astigma- 
tism, the light passing through the round hole appears oval, or 
it will be drawn into a vertical or horizontal stripe, varying ac- 
cording to the adjustment of the eye or its distance from the 
hole in the shade or shutter. 
If the daylight is passed through dark violet glass, or the 
lamplight through dark cobalt, to the astigmatic myope, the image 
will appear red with a blue border; to the astigmatic hyperme- 
trope, blue with red border. 
Abnormal regular astigmatism is divided by Donders into 
simple, compound, and mixed. In the simple form the eye is 
emmetropic in one of its principal meridians, and myopic or 
hypermetropic in the other, and is expressed E — = 0; the 
astigmatic deviation Ah = * or Am = *. If we find an eye nor- 
mal in the horizontal meridian, and myopic = 2o in its vertical, 
then Am — ; the proper lens to correct it would be a cylin- 
drical concave of 20" focus, axis horizontal. 
If the vertical meridian be normal, and the horizontal hyper- 
metropic — ,2, then Ah = and a convex cylindrical glass of 
12" focus, axis vertical, would neutralize it. 
Compound astigmatism: here the eye is myopic or hyper- 
metropic in all of its meridians, but not of a uniform grade; it 
is simple myopia, or hypermetropia with astigmatic variations. 24 
ASTIGMATISM. 
If there be in the vertical meridian M = Js> and in the horizon- 
tal M = le, then it is expressed M == 4\ 4* Am 24, for 48 + 24 = iV 
which is a myopia of 48 with an astigmatic variation of To 
correct this, it requires a spherico-cylindrical lens, one of the 
surfaces of which should be ground spherical concave 4S, the other 
cylindrical concave 2\; written — «s3 — 24 c, axis vertical. 
If there be in the horizontal meridian H = 3l0, and in vertical 
I! = l2> it is expressed H 3l() + Ah 2]„ and requires a lens one side 
spherical convex 30, the other cylindrical expressed 
30 s CT 20 c> axis horizontal. 
Mixed astigmatism is where myopia exists in one of the chief 
meridians and hypermetropia in the other; here, as the hyper- 
metropia in reference to the far point has a negative value as 
compared to the myopia, the astigmatic deviation is found by 
adding the refractive state. 
If there be M = in vertical, and H == 13 in horizontal merid- 
ian, then Amh =110+ i'5 = o- This may be corrected by a bi- 
cylindrical lens, one of whose surfaces is cylindrical convex 13, 
the other cylindrical concave ,o; written 15 C | 10 c, axis 
of concave surface to correspond to horizontal meridian. 
The above may also be corrected by a spherico-cylindrical 
lens, but the bi-cylindrical is preferable, on account of the pris- 
matic deviation and lateral distortion of objects that would be 
caused by the strongly-curved surfaces of the former. 
Irregular astigmatism is where planes of light in single 
meridians are broken up, so as to unite at two or more points. 
It arises from irregularities, either of the cornea or lens, and 
gives rise to diplopia, monocular polyopia, stellated figures of 
dispersion, etc., that cannot be entirely removed by correcting 
glasses. 
The asymmetrical formations of single meridians of the cor- 
nea, giving rise to doubling or multiplication of images, is usually 
the result of a shrinkage of cicatrices following wounds or ulcers; 
and generally, owing to the higher refractive power of the cor- 
nea, is much more disturbing to vision than when the irregular 
refractions in single meridians arise from inequalities in the sur- ASTHENOPIA. 
25 
faces of the lens. As these cicatrices usually only affect cer- 
tain parts of the cornea, it is sometimes requisite to cut out a 
portion of the iris, and thus make a new pupil, so as to admit 
the light through some portion of the cornea still retaining its 
normal curvatures. 
Astigmatic glasses should be made round, set in spectacle 
frames, and so adjusted that the axes of the cylindrical surfaces 
shall be exactly perpendicular to the direction of those princi- 
pal meridians having the greatest abnormal deviations. 
In high grades of astigmatism the same spectacles will not 
answer for distant and near vision. In converging the visual 
axes, the planes of the different meridians vary according to 
the amount of convergence, and perfect vision requires for each 
variation a new adjustment of the axes of the cylindrical sur- 
faces. Slight differences do not seriously lessen the sharpness 
of sight, but in attempting to look at minute objects through 
spectacles adjusted for the far point, the variation of the axes 
of the cylindrical glasses from the meridians to which they 
should correspond, is so great as to give rise to prismatic devia- 
tions and lateral distortion of objects, so disturbing to vision as 
to be unbearable to the patient. Hence, for near vision the 
glasses should be made to approach each other according to the 
amount of required convergence, and their surfaces should be 
so set as to be parallel to the planes of the pupils. 
ASTHENOPIA. 
The normal eye is adjusted for parallel rays, and only requires 
to be properly directed towards distant objects to give clear 
vision. To see distinctly near objects, the rays from which 
meet the cornea divergently, requires an adjustment produced 
and maintained by muscular action. Asthenopia is a want of suf- 
ficient potential muscular energy to maintain for any considerable 
length of time the proper adjustment of the dioptric apparatus 
for near vision of small objects, and the nervous and vascular 
excitement caused by the effort. If there is an insufficiency of 
the ciliary muscle, it is called accommodative asthenopia; if of 26 
ASTHENOPIA. 
the internal recti, it is distinguished as muscular asthenopia. 
The former is more frequently met with, and shows itself, for 
instance, in reading fine print; it is at first seen clearly, and 
sharply defined, but after a time it gradually becomes blurred, 
the borders widen out and grow indistinct; if the effort is con- 
tinued, it is followed by pain in the eyes and forehead, lachry- 
mation and conjunctival redness. If the book is laid aside, 
these symptoms quickly disappear, but return if the reading is 
too soon resumed. The frequent straining of the accommoda- 
tion in looking at near objects sometimes weakens the ciliary 
muscle to such an extent that it can maintain its adjustment 
but for a moment. The forced effort of the retina to catch a 
clear impression of an indistinct image causes it to become irri- 
table, sensitive to light, and hypersemic, accompanied by ciliary 
neuralgia, and redness of conjunctiva, rendering the eye unfit 
for use; hence near vision has to be for a time given up. 
Accommodative asthenopia is often the result of severe ex- 
hausting illness, which disappears with increasing strength.. 
Children of delicate organization and lax muscular fibre often 
suffer with it when they attend school. By far the most fre- 
quent cause is facultative hypermetropia; here a part of the 
accommodation is used for parallel rays; hence for near vision 
it requires a forced action of the ciliary muscle, whose po- 
tential energy becomes exhausted if the effort is too long contin- 
ued. Muscular asthenopia is also attended with retino-ciliary 
irritation; but here objects run into and overlap each other, or 
are seen double. It is most generally found in bathy morphia, and 
in high grades of myopia, where, for binocular vision, great con- 
vergence of the optic axes are necessary. If the myopia has pro- 
gressed slowly, the internal recti muscles may have gradually in- 
creased in size and strength sufficiently to perform the excessive 
labor demanded of them; but often, particularly if the disease 
has developed rapidly, there is a want of power of one or both 
of these muscles to long maintain the required tension; one fails 
and permits the external rectus to turn the eye outward, and the 
object is then seen double. When once the insufficiency of an ASTHENOPIA. 
27 
internal rectus has manifested itself, it does not readily regain 
its strength, even after a considerable period of rest; and it 
becomes less and less able to sustain prolonged action, until 
finally the insufficiency is so annoying that artificial assist- 
ance must be rendered, or binocular vision has to be given up. 
The weakness of the muscle can easily be shown by directing 
the patient to read fine print, held in the horizontal plane, or a 
little lower, before the eyes, and watching the result; soon 
one eye will be seen to waver for a moment, and then deviate 
outwards. Another test is to place a weak: prism before one of 
the eyes when adjusted for near vision, with its angle up or 
down. Few eyes can overcome a prism of 2° with its refrac- 
tive angle upwards or downwards, so as to fuse the double image, 
one of which will appear in a vertical line above the other. 
Single vision once removed, a muscle overstrained gives way, and 
seeks an equilibrium with its opponent according to the rela- 
tive strength of the two. When normal eyes are adjusted for 
the far point, only very weak prisms, with their angle 
outwards, can be overcome; but with the angle turned in- 
wards, the internal rectus can overcome a prism of from 20° to 
30°, so as to fuse the double image; but this difference dimin- 
ishes as the object approaches the near point, where the power 
of abduction and adduction is nearly equal. Here, if there is 
an insufficiency of one internal rectus muscle, the extent of it 
can be found by placing before one of the -eyes a weak prism 
with its angle up or down, while looking at a small ink spot on 
a piece of paper; soon the weakened muscle will waver, then 
give way, and the eye will turn outward. There will be 
two images of the object some distance apart laterally, and 
in different planes. Another prism with its angle out- 
ward, that will make these images stand in a vertical line one 
above the other, represents the degree of the insufficiency. 
In the treatment of asthenopia, care must be taken to avoid 
all work that strains or fatigues the eyes. The illumination 
should fall properly on the object, and not too direct on 
the eyes. Reading, writing, sewing, drawing, etc., should 28 
REMARKS. 
only be attempted in a good light, and then given up on 
the first appearance of symptoms of fatigue. In the accom- 
modative form, recourse must be had to convex glasses to 
relieve the overburdened muscle, and these must be of a power 
to correspond to the insufficiency; if this is slight, weak glasses 
will suffice, and nothing else is required; but if it is of a higher 
degree, stronger ones must be worn; but these destroy the asso- 
ciations that exist between accommodation and convergence be- 
yond what relative convergence can overcome; hence, the con- 
vex glasses must be combined with a weak prism, with its 
angle outward. The lens should be ground on the surfaces of 
the prism, so as to combine both in one glass. 
Muscular asthenopia being usually the result of myopia, 
requires concave glasses in order to remove the apparent 
distance of the object, and thus diminish the convergence 
of the optic axes. These may answer where the myopia is 
of low degree, but in the higher grades negative glasses 
that would neutralize the insufficiency of the internal recti 
muscles by diminishing the convergence, would so reduce the 
size of the image as to render vision indistinct; hence, the over- 
burdened muscles must be relieved by weak prisms with angles 
outwards. Generally, prisms whose refractive angle is a little 
less than the amount of insufficiency answers, combined with 
negative glasses that enables the patient to do moderately fine 
work without fatigue to the eyes. Where the insufficiency of 
only one muscle is considerable, it is better to divide the pris- 
matic correction between the two eyes, as strong prisms cause 
chromatic aberrations and lateral distortion of objects very 
troublesome to the patient. Some surgeons have advised the 
laying back the attachment of the external rectus muscle, and 
thus weaken the opposing power to the rectus internus, but the 
results have not been very satisfactory. 
REMARKS. 
For most of our knowledge of the diseases of refraction and 
accommodation, we are indebted to the researches of that won- REMARKS. 
29 
derful people the Germans, who at the present day surpass all 
other nations in diving into the hidden depths of Nature, in 
order to investigate the mysterious secrets of her workings, and 
then applying the knowledge thus attained to benefit mankind 
and to relieve human suffering. 
Among those worthy of all honor in connection with the 
subjects of this article, I would mention Hemholtz, Donders, 
Graefe, Knapp,* Arlt, Stellwag, Jaeger, and Hering, who, with 
their fellow-colaborers, have, in less than a quarter of a cen- 
tury, built up an entirely new science in this department of 
ophthalmology. 
* This world-renowned Ophthalmologist has recently made America his 
home.