THE LIBRARY
OF
THE UNIVERSITY
OF CALIFORNIA
'OTOMETRY
GIFT OF
Dr. Hugh V. Brown
SQUINT
ITS CAUSES, PATHOLOGY, AND
TREATMENT
SQUINT:
ITS CAUSES, PATHOLOGY
AND TREATMENT
BY
CLAUD WORTH, F.R.C.S.
PHILADELPHIA
P. BLAKISTON'S SON AND CO.
1012 WALNUT STREET
1906
Add'l
GIFT
Re
OPTOMETRY
UBKA-
CONTENTS.
CHAPTER I.
Introduction page i
CHAPTER II.
BINOCULAR VISION.
Binocular vision — Grades of binocular vision — Tests
for binocular vision — The normal development of the
fusion sense in infancy .... page 7
CHAPTER III.
CONVERGENT SQUINT.
General description of the anomaly — Clinical varie-
ties — Suppression of the vision of the deviating eye —
Diplopia artificially produced — Nature of diplopia —
The amblyopia of convergent squint — The power of
central fixation in the deviating eye — False fixation —
False macula — Monocular diplopia — Apparent vertical
deviation — True vertical deviation — Spurious squint of
infants — Spontaneous " cure " of squint — Course of an
untreated case of squint — Age of onset of squint —
Refractive error in convergent squint — Statistical
tables — Relative frequency of squint . . page 25
CHAPTER IV.
THE ^ETIOLOGY OF CONVERGENT SQUINT.
Muscle theory — Donder's theory — ^Etiology of con-
vergent squint — Defect of the fusion sense the funda-
mental cause — Subsidiary causes — Proofs of the Author's
contention ....... page 48
292
vi. CONTENTS
CHAPTER V.
AMBLYOPIA, CONGENITAL AND ACQUIRED.
Congenital amblyopia — Acquired amblyopia —
Illustrative cases — Amblyopia in cases of convergent
squint — Statistical tables .... page 63
CHAPTER VI.
THE METHOD OF INVESTIGATING A CASE OF SQUINT.
History— The character of the squint — Cover test —
Mirror test — Diagnosis between squint and paralysis
— The power of central fixation — The movements of
each eye separately — Dynamic convergence — Vision
testing — Snellen's types — The ivory-ball test — The
examination of the fusion sense — Measurement of the
angle of the deviation — The Deviometer — Maddox
tangent scale — Priestley Smith's tape — The perimeter
— Estimation of refractive error . . page 78
CHAPTER VII.
THE TREATMENT OF CONVERGENT SQUINT.
The objects of treatment — The means by which
these objects may be attained — Optical correction —
Spectacles for children and for infants— Occlusion of
the fixing eye— Instillation of atropine into the fixing
eye only — Fusion training — Operation — Indications for,
and choice of, operation — Alternating squints — Occa-
sional squints— Vertical deviations . . page 97
CHAPTER VIII.
THE METHOD OF TRAINING THE FUSION SENSE.
Preliminary remarks — The age at which the fusion
sense may be educated — The Amblyoscope— Its illu-
minating apparatus — Three classes of object slides —
Fusion training— The method of overcoming ^"sup-
pression" Simultaneous vision — Fusion of images —
Increasing the amplitude of fusion . . page Il8
CONTENTS VII.
CHAPTER IX.
DIVERGENT SQUINT.
Myopic divergent squint — Neuropathic divergent
squint — Non-comitant divergent squints other than
paralytic — Divergence in extreme myopia — Divergence
of blind eyes — Divergence secondary to tenotomy
page 133
CHAPTER X.
TREATMENT OF SQUINT.
Illustrative cases page 141
CHAPTER XI.
HETEROPHORIA.
Orthophoria — Heterophoria — Methods of testing
the muscular balance of the eyes — Esophoria —
Exophoria — Hyperphoria — Cyclophoria — Illustrative
cases page 164
Insufficiency of dynamic convergence . page 196
CHAPTER XII.
OPERATIONS ON THE EXTERNAL OCULAR MUSCLES.
Advancement of a rectus muscle — The author's
advancement operation — Musculo-capsular advance-
ment — -Secondary advancements — Tenotomy — Com-
plete central tenotomy .... page 201
APPENDIX.
Details of cases of congenital amblyopia— Prisms
and decentred lenses — Results of fusion training —
Results of advancement operations — Details of con-
struction of the deviometer — Modifications of the
amblyoscope — Advancement forceps . page 210
INDEX.
PREFACE TO THE FIRST EDITION.
By examining- a very large number of cases
of squint, and watching the results of treatment
during a number of years, and by investigating
the visual functions of normal-sighted people,
I have endeavoured to learn the causes and
pathology of squint. The methods of treatment
which I employ are the outcome of these
observations.
In cases of constant unilateral convergent
squint, the usual routine treatment, by glasses
and operation, gives extremely unsatisfactory
results. In about one-third of these cases, the
wearing of glasses causes the eyes, after a time,
to become "straight." In the other two-thirds,
the deformity may be more or less removed by
operation. But, more often than not, the deviat-
ing eye becomes very blind, and the acquisition
of any sort of binocular vision is quite the
exception.
On the other hand, cases of unilateral squint
in which treatment is commenced early and
carried out by the methods described in these
pages are nearly always perfectly cured, having
good vision in each eye, and good binocular vision.
Since 1893 I have kept detailed notes of every
case of squint which has come under my observa-
tion. I have notes of 2,337 squints and hetero-
phorias. Of these cases, 1,729 suffered from
convergent squint. The cases presented them-
selves in the out-patient departments of the West
Ham and East London Hospital, the Lough-
borough Hospital, and the Royal London
Ophthalmic Hospital (Moorfields), and in my
private practice.
I am greatly indebted to Mr. Silcock and
Mr. Holmes Spicer for their kindness in allowing
me, during a period of nearly four years, to
investigate and treat the cases of squint attending
their out-patient clinics at Moorfields.
I wish to thank Mr. R. E. Hanson for valuable
assistance in working out the statistics of my cases.
138, Hurley Street,
London, IT.
May, 1903.
PREFACE TO THE SECOND EDITION.
I take this opportunity to thank my confreres,
both at home and abroad, for the very generous
reception accorded to the work.
In preparing- the second edition, nothing has
been altered or omitted. But some small addi-
tions have been made, and some matters more
fully discussed.
Dr. E. H. Oppenheimer has translated the
book into German (for Messrs. Julius Springer
and Co., Berlin).
PREFACE TO THE THIRD EDITION.
The third edition contains statistics which
give a fair idea of the results which may be
expected from the methods of advancement and
fusion training described in these pages.
May, 1906.
SQUINT:
Its Causes, Pathology and Treatment.
CHAPTER I.
INTRODUCTION.
This chapter contains nothing new. It deals
very briefly with certain elementary facts.
EMMETROPIA is the refractive condition of the
normal adult human eye. Rays of light proceeding
from a single point on a distant object may, for
practical purposes, be regarded as parallel. When
these parallel rays enter an emmetropic eye, they
undergo refraction as they pass through the refracting
media (cornea, aqueous humour, lens, vitreous humour),
and are brought to a focus on the retina. Rays from
every other point in the distant object are similarly
focussed, so that a complete (inverted) image of the
object is formed on the retina. The refraction which
takes place under these conditions is called the static
refraction of the eye.
Accommodation. — Rays of light which enter the
eye from a near object, e.g., a printed page, are sensibly
divergent. Now, it is obvious that the static refrac-
tion of the normal eye, which exactly suffices to bring
parallel rays to a focus on the retina, will not accu-
rately focus these divergent rays. To meet this
2 INTRODUCTION
deficiency, there is a muscle within the eyeball, the
ciliary muscle, which, by its contraction, causes the
lens to become more convex, more nearly spherical,
and so increases its refractive power. This act of
increasing the refractive power of the eye is called
accommodation, and the additional refraction thus pro-
duced is called the dynamic refraction of the eye.
Presbyopia. — In childhood the lens is very soft
and elastic, and is easily made to change its shape
under the action of the ciliary muscle, so that children
have a very wide range of accommodation. As age
advances, the lens gradually becomes more and more
firm and incompressible, so that, though distant objects
are still perfectly focussed by means of the static
refraction of the eye, the increase of refraction, pro-
duced by the action of the ciliary muscle on the lens,
becomes, after a time, insufficient for the focussing of
near objects. For this reason, a normal-sighted person
of fifty must either hold his book at a greater distance,
in order that the rays of light proceeding therefrom
shall be more nearly parallel, or he must supplement
his weakened accommodation with a pair of convex
glasses.
Atropine, when instilled into the conjunctival sac,
has the property of temporarily paralysing the ciliary
muscle, and so suspending entirely the power of
accommodation. An atropised normal eye sees dis-
tant objects distinctly, by virtue of its static refraction,
but is quite unable to focus the divergent rays pro-
ceeding from a near object. In other words, atropine
produces an artificial presbyopia.
FIXATION. — In the centre of the retina is the macula
Intra, whieh, in the human eye, is far more sensitive
to ordinary visual impressions than any other part.
It is desirable, therefore, that the eye be brought into
such a position that the image of any object which
especially engages our attention shall be formed upon
tin- macula lutea. The eye is then said to " fix " the
INTRODUCTION 3
object. An imaginary line, passing from the centre
of the macula, through the optical centre of the eye, to
the object looked at, is called the visual axis.
Convergence. — When the two eyes look at a dis-
tant object, the visual axes may, for practical purposes,
be considered to be parallel. When, however, a near
object is looked at, the two eyes must rotate inwards,
in order that both visual axes may be directed to the
same object. This active inward rotation of the eyes
is called dynamic convergence. In the case of a normal
pair of eyes there is no such thing as static convergence,
because the primary position of the visual axes is one
of parallelism. In a case of convergent squint, how-
ever, there is a static convergence corresponding to the
angle of the deviation.
Accommodation and Convergence. — When a
person with a normal pair of emmetropic eyes looks
at a near object, the eyes converge in order that both
visual axes may be directed to the object. At the
same time each eye "accommodates," in order that the
rays of light from the object may be accurately
focussed on its retina. These two functions, ac-
commodation and convergence, are, in ordinary
life, always used together, so that they have become
" associated " by hereditary and individual habit. It
is difficult, therefore, for a normal pair of eyes to
accommodate without converging or to converge
without accommodating.
Conjugate Movements. — In looking to the right,
or left, or up, or down, the two eyes move together
through exactly the same angle.
Movements oe each Eye Separately. — The
extreme range of upward and downward rotations of
a single eye varies slightly in different people, the
average being about 46° up and 56° down. 1 Outward
1 These figures are the average of measurements which
I made on 64 normal-sighted persons with Stephens'
tropometer.
4 INTRODUCTION
rotation (abversion) may be considered full when the
edge of the cornea can be made to touch the outer
canthus. The power of inward rotation (adversion)
varies considerably in different people. Most people
can advert each eye separately through an arc of 50 .
The power of independent adversion tends to become
less as age advances.
Hypermetropia. — For purposes of discussion, the
refracting media of the eye may be diagrammatically
represented as a simple convex lens. In the emme-
tropic eye, as already explained, the strength of this
lens is such that parallel rays of light are brought to a
focus exactly at the retina. A hypermetropic eye is
shorter, from before backwards, than the emmetropic
eye. This abnormal shortness causes the retina to be
situated too near this diagrammatic lens. Now, in
order that parallel rays may be brought to a focus on
this abnormally situated retina, the focal length of the
diagrammatic lens must be shortened, or, in other
words, the strength of the lens must be increased.
This increase in strength may be brought about either
by the patient's using his accommodation in distant
vision (and still more, of course, in near vision) or by
his wearing a convex spectacle lens in front of the eye.
A hypermetrope may be able easily to accommodate
sufficiently to correct his refractive error in distant
vision, but may have difficulty in sustaining the addi-
tional effort of accommodation involved in looking at
a near object, e.g., in reading.
Myopia is the converse of hypermetropia. A myopic
eye is abnormally long from before backwards, so that
the retina is at a greater distance from the centre of
our diagrammatic lens than is the case in the em-
metropic eye. In order, therefore, that parallel rays
from a distant object shall be iocussed on the abnor-
mally situated retina, the focal length of the diagram-
matic lens must be increased, /.<•., the strength of the
lens must be diminished. The only way in which this
INTRODUCTION S
can be accomplished is by putting a concave spectacle
lens in front of the eye.
If an indistinctly seen distant object be gradually
brought nearer a myopic eye, the rays which enter the
eye therefrom become more and more divergent, till
a point is reached at which the static refraction of the
myopic eye is just sufficient to focus these divergent
rays. If the object be brought still nearer, the eye
accommodates and so still sees distinctly.
Astigmatism. — In the human eye, the greater part
of the refraction takes place at the surface of the cornea,
where the rays of light pass from the air into the much
denser medium, the corneal substance. The normal
human cornea is approximately a segment of a sphere.
Sometimes, however, the cornea is curved more in one
meridian than in another, so that it is slightly oval —
like a slice from the side of a cocoa-nut. This condi-
tion is called astigmatism. In the meridian of greater
curvature the rays will be refracted more, and brought
to a focus sooner, than in the meridian of less curva-
ture. Consequently the picture formed on the retina
will be blurred and indistinct. In order to equalise
the refraction in the different meridians, a cylindrical
lens must be used, i.e., a lens which is curved in one
direction only.
Anisometropia is an inequality in the static refrac-
tion of the two eyes.
Angle Gamma. 1 — The visual axis does not exactly
correspond with the geometrical antero-posterior axis
1 The angle gamma which I have described is the angle
which is measured clinically and is of practical importance.
But, since the visual axis need not necessarily pass through
the centre of motion of the eye-ball, mathematicians have
taken as one of the boundaries of the angle gamma a line
passing through the centre of motion of the eye-ball to the
object looked at. This line is of no clinical significance,
as its direction cannot be determined except on paper.
2
6 INTRODUCTION
of the eye-ball. The angle between the visual axis and
the antero-posterior axis of the eye-ball is called the
angle gamma. Usually the visual axis passes through
the pupil to the nasal side of its centre. Rarely it
passes through the pupil to the temporal side of its
centre, in which case the angle gamma is said to be
negative.
In hypermetropic eyes the angle gamma is usually
high, so that, when the visual axes are parallel, the
antero-posterior axes of the eye-balls are perceptibly
divergent. In this way a deceptive appearance of
divergent squint may be produced or a slight con-
vergent squint may be masked.
In myopic eyes the angle gamma usually is low or
even negative. In the latter case, while the visual axes
are parallel, the antero-posterior axes of the eye-balls
are convergent, so that convergent squint may be
simulated or a slight divergent squint masked.
CHAPTER II.
BINOCULAR VISION.
When the eyes are in the primary position
(i.e., looking straight ahead into the distance)
the fields of vision of the two eyes overlap every-
where, except in a sector of about 35 towards
the temporal periphery of each field. In other
words, everything which a normal-sighted person
sees, he sees with both eyes simultaneously,
except objects which lie on his extreme right
or his extreme left. These are seen only with
one eye.
When a distant object engages our attention,
the two eyes are brought into such a position
that a picture of the object is formed simul-
taneously on the central part of each retina.
Similarly, all other distant objects, within the
limits of overlapping of the visual fields, are
focussed on functionally corresponding parts of
each retina. The impressions thus received
from the two eyes are blended in the brain, so
that we are conscious only of one single picture.
This psychical blending of the two sets of visual
impressions is called binocular vision.
The binocular vision of near objects is a more
BINOCULAR VISION
*° s
: i
Fig. i.
BINOCULAR VISION 9
complex act, inasmuch as the brain has to blend
images which, for the most part, do not fall upon
geometrically corresponding points of the two
retinae.
The diagram represents a pair of eyes looking
at an object O in the middle distance. An image
of O is formed on the macula ML and MR of
each retina. Now, it is obvious that only objects
lying in the line MR— O (or in this line produced
beyond O) can be focussed on the macula of the
right eye. Similarly, only objects lying in the
line ML — O can be focussed on the macula of
the left eye. O 2 is an object lying in the line
MR — O. An image of O 2 will be formed on the
macula of the right eye. But the image of O 2
formed in the left eye will not be on the corre-
sponding point, but at a point X, considerably
to the outer side of the macula.
Take a practical illustration — look steadily at
a distant object, and hold a finger about 18 inches
in front of the eyes. The finger will be seen
double, the left image corresponding to the right
eye, and the right image to the left eye (crossed
diplopia). Now look at the finger, and the
distant object will appear double, the diplopia
this time being homonymous.
This "physiological diplopia" must be con-
stantly present, in looking about a room for
example, yet we are not ordinarily conscious of
seeing double. This customary freedom from
IO BINOCULAR VISION
diplopia is brought about, not by mental sup-
pression of one of the images, but by the mar-
vellous elasticity of the fusion faculty. Both
sets of impressions reach the brain, and, by their
combination, assist in our appreciation of the
third dimension.
A simple experiment will demonstrate the
elasticity of fusion. Place in the amblyoscope
(chapter viii.) the slides shown in fig. 13, p. 124.
The two slits are fused into one, and the control
marks are seen, one on each side. Now gradually
diverge the tubes. When the extreme limit of
divergence of the visual axes has been nearly
reached, fusion of the slits is still maintained, but
the control marks recede on each side farther
and farther from them. When the limit is
passed and fusion can no longer be maintained,
the slits suddenly spring apart. As each slit is
on the same slide with its control mark, the
distance cannot really vary ; but, within certain
limits, the mind still fuses the images of the slits,
even when they no longer fall upon anatomically
corresponding points of each retina. This experi-
ment would serve as a proof, were any needed,
that fusion is a purely psychical process, and not
merely the result of stimulation of corresponding
sets of nerve endings in each retina.
But this must not be taken to indicate that
accurate adjustment of the relative positions of
the two eyes is unnecessary. The law governing
BINOCULAR VISION
the fusion of images which are not precisely
similar may be stated as follows : When the
images formed in the two eyes differ in shape,
size, or position, if the disparity be not too great,
the oculo-motor apparatus first places the eyes
in the most favourable relative positions ; the
fusion sense, by virtue of its elasticity, then fills
lip any gap ivhich may remain.
The following additional experiments were suggested
to me by Dr. Verhoeff, of Boston, U.S.A.
Fig.
Fig. 3.
Fig. 4.
Fig. 5.
Fig. 6.
Place fig. 2 and fig. 3, in a stereoscope. The
horizontal lines of course are blended. But the
oblique lines also are blended; the resulting line
appearing perpendicular to the horizontal line. This
1 2 BINOCULAR VISION
blending of the oblique lines cannot be accomplished
by any rotation of the eyeballs round a fore and aft
axis, as, in this case, the horizontal lines would not be
blended.
Again, if figs. 4 and 5 be blended in a stereoscope
the combined image resembles fig. 6. The oblique
lines outside the circles are blended into a perpendi-
cular line, but the part within the circle, which is seen
with one eye only, retains its oblique direction.
In a case in which each eye separately has
the power of seeing, but in which binocular vision
is absent, one of two conditions must be present,
either (a) the mind is separately conscious of
the two sets of impressions received from the
two eyes — diplopia, e.g., in paralysis of an
external ocular muscle ; or (b) the mind takes
note only of the impressions received from one
eye and ignores those received from the other
— suppression, e.g., in an ordinary case of con-
vergent squint.
Grades of Binocular Vision.
Most people who have binocular vision have
the faculty to its full extent. Anyone, however,
who has undertaken the orthoptic training- of any
considerable number of squinters, will find that
those who see binocularly naturally arrange them-
selves into three separate and distinct classes,
according to the degree in which they possess
the faculty.
These may be called : —
BINOCULAR VISION I 3
First Grade. — Simultaneous macular perception.
Second Grade. — True fusion with some ampli-
tude.
Third Grade. — Sense of perspective.
First Grade. Simultaneous macular percep-
tion. — A patient having only this grade of
binocular vision sees devices in a stereoscope
as two separate pictures, which overlap and form
one only when they are put in certain relative
positions corresponding to the directions indepen-
dently assumed by the visual axes. The " desire "
for binocular vision is absent, so that no effort
will be made to maintain fusion.
Second Grade. True fiision with some ampli-
tude. — A person having the second grade of
binocular vision not only fuses the retinal images
in the two eyes, but can make some effort to
maintain fusion. When such a person is fusing
the pictures in a stereoscope, if the pictures be
separated or brought together the eyes will, to
a certain extent, follow them in the interest of
binocular vision.
Third Grade. Sense of perspective. — The two
eyes see from different points of view. In looking
at any solid object, such as a pillar, for instance,
the right eye will see more of the right side of
the object and the left eye more of the left side.
In the slightly dissimilar pictures thus focussed
on the retinas the points of difference are not
suppressed, as in the case of a person having
14 BINOCULAR VISION
only the second grade, neither is the observer
conscious of diplopia. The psychical blending of
the two slightly dissimilar sets of visual impres-
sions enables him to appreciate the solidity of
surrounding objects and assists in his judgment
of their relative distances.
There is a wide gap between grades i and 2.
A patient, however, who has grade 2 usually
acquires the third grade also.
Quite as important as the grade of binocular
vision is its intensity. A person whose fusion
sense is feebly developed may possibly, under
favourable conditions, have the highest grade
of binocular vision. But the intensity of his
tendency to fusion will be slight, so that, under
unfavourable conditions, he easily abandons the
effort and uses one eye only. One, however,
whose fusion sense is well developed will have
such an intense tendency to binocular vision that
nothing will make him abandon it while both
eyes are open. (Except, of course, a muscular
paralysis, in which case he will suffer from
persistent and intolerable diplopia.)
Tests for Binocular Vision.
Four dot test. — A convenient clinical test,
which I have used constantly for some years,
is an adaptation of Snellen's coloured glasses.
For want of a better name, it may be called
the " Four dot test." A pure red glass allows
BINOCULAR VISION
only the red rays of light to pass through it.
A pure green glass transmits only the green
rays. Therefore light which has passed through
Fig. 7-
the red glass cannot be seen at all through the
green glass, and vice versa.
A piece of plain ground glass, 1 2 inches by 9
inches, is covered on the back with opaque black
paper. The black paper has four round holes cut
in it, each 3 inches in diameter, as shown in the
I 6 BINOCULAR VISION
diagram. The lower hole is left clear. Behind
the upper hole is cemented a piece of red glass.
Behind each of the other two is cemented a piece
of green glass. The arrangement is mounted in
the front of a box which contains an electric or
other bright light.
The patient, standing five or six yards away,
wears a trial frame with a red glass before the
right eye and a green glass before the left. If
now he sees two dots (white and red) he is
using the right eye only. If he sees three dots
(white and two green) he is using the left eye
only. If he sees four dots (white, red, and two
green) he uses both eyes, and has at least grade
i binocular vision. If he sees five dots (red,
two green, and the white seen double) he has
diplopia. If the accuracy of the patient's answers
be doubted, it may be tested by changing the
glasses in the spectacle frame from one eye to
the other.
The amblyoscope (see chapter viii.). — Adjust
the instrument for parallelism of the visual axes.
Place in the slots the slides shown in fig, 13.
If the patient sees the two slits as one, and, at
the same time, sees both the dot and the cross,
he has grade 1 binocular vision. Now diverge
or converge the tubes of the instrument. If this
can be done, even to a very slight extent, while
the patient still fuses the slits and sees both
control marks, he has grade 2 binocular vision.
BINOCULAR VISION I 7
For children, more interesting objects, such
as figs. 1 6 and 17, may be used in the same
way. The extent to which the tubes may be
separated or brought together without the eyes
becoming dissociated, may, for practical pur-
poses, be taken as a measure of the degree of
development of the fusion faculty.
Now put in the instrument the slides shown
in fig. 18. A patient with grade 2 binocular
vision will only fuse the outer circles ; but he
will either suppress the image of one of the
inner circles, or will see both inner circles " all
mixed up." A person, however, with grade 3
binocular vision sees the inner circles blended
and appearing much nearer the eye, giving the
whole device the appearance of a tub or bucket
bottom up. If the slides be now changed from
one tube to the other, the inner circle will seem
farther away, as if he were looking at the inside
of the tub. This appearance is so vivid that
even young children can tell at once whether
they are looking at the outside or the inside of
the tub. By changing the slides from one tube
to the other two or three times, guessing on
the part of the patient is rendered impossible.
I know no better test for the " sense of per-
spective."
Herings drop test for the sense of perspective.
— I do not now use this test clinically. The
experiment is, however, very instructive.
I 8 BINOCULAR VISION
The test apparatus (fig. 8) consists of a shallow
box (of about the size and shape of a box for
twenty- five large cigars), open at both ends.
From one end two arms project. The extremi-
ties of these two arms are joined by a fine thread,
on the middle of which is a round bead.
Fig.
The patient holds the open end of the box
close to his eyes, and looks through the box,
at the bead. The surgeon now drops small
objects of various sizes, such as cowrie shells,
sometimes on one side of the thread, some-
times on the other. The patient is asked to
say whether each shell, as it drops, falls on the
near side or the far side of the thread.
BINOCULAR VISION I 9
If he has the third grade of binocular vision,
" the sense of perspective," he will almost always
answer correctly. If he has not, his answers
will be mere guesses, and he will be nearly as
often wrong as right.
The principle of the test is as follows : — The
box cuts off all view of surrounding objects,
including the hands of the surgeon. The size
of the falling objects varies, so that their appa-
rent size gives no information as to their distance.
The view of the falling object is too brief to
admit of any movement of accommodation or
convergence, or any lateral movement of the
patient's head. The patient is thus deprived
of all auxiliary means of judging distances, and
has to depend upon his "sense of perspective"
alone.
This test is not infallible. I once made the dis-
covery that a boy, aged n, with a manifest squint
of 1 3 , could tell on which side the shell fell, almost
every time, when both eyes were open. When, how-
ever, I covered the deviating eye his answers were
as often wrong as right. He had, in the deviating
eye, & vision. There was no " false macula." He
had no diplopia spontaneously, but it was easily elicited
with a candle and coloured glasses. I have since met
with other similar cases. The explanation is probably
this : — In trying the test with a normal pair of eyes,
the view of the falling shell is so brief that there is no
time for the eyes " to fix " the shell, so the images of
the object do not fall upon corresponding parts of the
two retinae. It is not, therefore, really a test for the
sense of perspective in direct vision, but a test for
20 BINOCULAR VISION
the subconscious perception of " physiological dip-
lopia " in more or less eccentric parts of the retinae.
In none of these cases was the suppression of the
vision of the deviating eye very profound, so that a
moving object would probably be perceived. As
strictly corresponding points are not required in this
test, it seems not unlikely that the mind may derive
some information from the false image', by making
allowance for the faulty position of the deviating eye.
This is not difficult to believe when we remember
that, in a case of squint in which diplopia has been
artificially elicited, the angle of the diplopia is often
very much smaller than that of the squint ; show-
ing that the mind ordinarily makes some allowance
for the position of the squinting eye.
The Normal Development of the Fusion
Sense.
In two large creches I made experiments,
extending over nearly a year, with the object
of gaining some knowledge of this subject. It
would be tedious to describe in detail the
methods employed. I therefore give a general
summary of results.
From the earliest infancy the pupillary light
reflex and the fixation reflex are present, showing
that some degree of vision of each eye, and the
preponderance of the macula region, are innate.
If, in a darkened room, the light of a candle be
suddenly thrown from an ophthalmoscope mirror
into an eye of an infant only a few hours old,
the eye will immediately fix the mirror. This
fixation is purely reflex and is only maintained
BINOCULAR VISION 2 1
for an instant. During the first few days of life
the infant cannot fix a steady light, but, by
suddenly flashing the light into the eye, this
reflex fixation may be repeatedly obtained.
At the end of two or three weeks most infants
will fix the mirror steadily for several seconds
at a time with one or other eye, but will not
converge both visual axes accurately in looking
at a near object.
At the age of five or six weeks, as a rule, the
positions of the reflections of the mirror on the
child's corneae are symmetrical, showing that
the child is fixing the mirror binocularly. But,
now and then, one eye turns a little inwards, or
more rarely outwards, while the other fixes the
mirror.
During the first few months of life the move-
ments of the eyes are uncertain, not completely
controlled by the higher centres of the brain.
The eyes move more or less together, but the
slightest gastric or other disturbance often causes
one or other eye to deviate. But it will be
noticed that this want of coordination is confined
to movements in the horizontal plane. The
conjugation of the two eyes for vertical move-
ments is well-developed from the earliest infancy :
one does not see one eye turn up or down
without the other.
We can scarcely suppose that any degree of
binocular vision can be present at a time when
3
22 BINOCULAR VISION
the coordination of the eyes in horizontal move-
ments is in this rudimentary condition.
A little later, at the age of five or six months,
if the child's attention be engaged by some new
and bright object of absorbing interest, such as
a cut glass decanter - stopper revolved before
a candle flame, it will often be possible for the
person nursing the child to slip a large prism
before one of his eyes without his appearing
to notice it. A prism displaces the image of an
object towards its apex. Therefore, if binocular
vision is to be maintained, the eye must also
rotate in the direction of the apex of the prism.
If a prism of, say, 12° has been successfully
slipped before one of the child's eyes, with the
apex towards the nose, the eye will, in many
cases, make a slight inward rotation, showing
that the child has some sort of binocular
vision. In some cases, however, while the
naked eye continues to be steadily directed
towards the object, the eye behind the prism
makes no inward rotation. The vision of this
eye is probably suppressed. These resemble
certain cases of occasional squint, in which
binocular vision is present when the eyes are
"straight," but suppression of the vision of the
deviating eye takes place when the squint is
manifest.
After the end of the first year, a child who
allows one to make the experiment with the
BINOCULAR VISION 23
prism apex inwards will almost always turn
in the eye in order to blend the images.
When the experiment is tried with the prism
apex up or down, it is, of course, not possible for
the eye to make an independent vertical move-
ment in order to blend the images. I tried this
vertical prism with some of the more tractable
infants, aged twelve to eighteen months, who had
readily made the compensating inward movement
when tried with the prism apex in. Some of them
showed their disapproval of the vertical prism
by screwing up the eyes and twisting the head.
Others made up-and-down conjugate movements
of both eyes, sometimes directing their attention
to the upper image and sometimes to the lower.
To recapitulate — The vision of each eye
separately, the preponderance of the macular
reo-ion, and the conjugation of the two eyes in
vertical movements, the human infant has fairly
well developed at birth. The conjugation of
the eyes for horizontal movements (intended to
subserve the function of binocular vision) is
perfected within the first few months of life.
Between five and six months one finds the first
certain evidence of a " desire for binocular
vision," though probably a certain degree of
binocular vision is present at a much earlier
period. At first, if any obstacle be interposed,
it is a question whether an effort shall be made
to overcome it, or whether the newly acquired art
24 BINOCULAR VISION
shall be abandoned and the vision of one eye
temporarily suppressed. Towards the end of the
first year the eyes will make a considerable effort
in the interests of binocular vision. If the
obstacle prove insuperable the child suffers from
diplopia, being no longer able to suppress the
vision of one eye.
The results of fusion training in the case of
squinters would seem to show that the fusion
faculty normally reaches its full development
before the end of the sixth year.
25
CHAPTER III.
CONVERGENT SQUINT.
In most of the text-books squint is defined
somewhat as follows : " Squint consists in a
deviation of the visual axis of one of the eyes
from the correct position of fixation." The
authors have mistaken a single symptom for the
whole disease. One might as well describe Pott's
disease as "a deviation of the spine from its
normal shape."
Two essential conditions are present in every
case of comitant convergent squint.
(i) An abnormal convergence of the visual
axes.
(2) A defect of the fusion faculty.
Other conditions may also be found : —
(3) The vision of the eye which is not being
used for fixation is almost invariably suppressed.
(4) There is, in rather rare instances, more or
less congenital amblyopia.
(5) There is very often acquired amblyopia in
the deviating eye, as the result of neglect or
inefficient treatment.
(6) There is usually a refractive error, com-
26 CONVERGENT SQUINT
monly hypermetropia and hypermetropic astig-
matism.
J\In a healthy person, with a normal fusion
faculty, the " desire for binocular vision " causes
the two eyes to be directed steadily to the same
object. But when the " desire for binocular
vision " is absent there is no special reason for
this perfect accord between the movements of the
two eyes, so that any slight cause may then upset
the equilibrium of the convergence centre, and so
cause the visual axes to assume permanently
faulty relative directions (see chapter iv.).
Then, when the patient is looking at a distant
object, instead of the visual axes being parallel
they are convergent. But, in order to see the
object distinctly, the patient must look directly at
it with one or other eye. He will naturally
choose the eye which has the smaller refractive
error. He cannot overcome the abnormal con-
vergence, neither can he move one eye without
the other. He therefore makes a conjugate
lateral movement of both eyes until he has
brought the better eye into the required position,
the other eye turning still more in towards the
nose. So that the better eye becomes " straight,"
and the worse eye manifests the convergence of
both. The eye which is used for vision is called
the fixing eye ; the other eye is called the
squinting or deviating eye.
If a patient fixes, say, with the right eye and
CONVERGENT SQUINT 2J
turns in the left, he is said to have convergent
squint of the left eye. This is a useful conven-
tion, but it must be remembered that it does not
accurately describe the condition, as, of course,
convergent squint really concerns both eyes and
certain cerebral functions as well.
Sin a case of convergent squint the separate
movements of each eye are perfect. When one
eye is covered, the other eye can move upwards
(superversion), downwards (subversion), inwards
(adversion), and nearly always outwards 1 (ab-
version) to the normal extent.
The conjugate movements of the two eyes are
perfect. When the fixing eye moves in any
direction, the deviating eye also moves through
exactly the same angle. When the (previously)
fixing eye is screened, and the patient fixes with
the (previously) squinting eye, the screened eye
manifests a deviation exactly equal to that for-
merly exhibited by the other eye.' 2 In other
words, the squint is comitant.
The association between accommodation (dy-
1 In 1,523 cases of convergent squint, in which I noted
the power of abversion of each eye separately, I found
it perfect in 81 per cent. The remaining 19 per cent.,
in which abversion was deficient, were almost all cases
of long standing. The defect of abversion was less un-
common the longer the duration of the deviation.
2 In a case of uncorrected anisometropia the patient may
accommodate to a different degree, according to the eye he
uses. This may make the squint appear to be not strictly
comitant.
28 CONVERGENT SQUINT
namic refraction) and dynamic convergence is
perfect. When the fixing eye, after looking at
a distant object, suddenly accommodates for a
near object, the squinting eye rolls still further
inwards, a dynamic convergence being super-
added to the abnormal static convergence. This
dynamic convergence is proportionate to the
extra effort of accommodation involved in looking
at the near object.
In fact, there is no motor defect of any kind
in a typical case of convergent squint, but the
primary position from which these movements
start is a "cross-eyed" position instead of
parallelism of the visual axes.
Convergent squint presents certain clinical
varieties. These may be classified as follows : —
(i) Occasional squint, of which there are two
classes : (a) Premonitory occasional. (6) True
occasional.
(2) Constant unilateral squint.
(3) Alternating squint, of which there are two
distinct classes : (a) Accidentally alternating-
squint. (6) Essentially alternating squint.
( 1 ) Occasional squint. — A patient is said to
have an occasional squint if the eyes are only
occasionally seen to deviate from their normal
relative directions. When no deviation is present,
the patient usually has the first grade of binocular
vision. When he squints he, in the majority of
cases, has no diplopia. The deviation of an occa-
CONVERGENT SQUINT 2Q.
sional squint is in some cases only seen for a few
seconds in the day, in others the eyes are almost
as often "crossed" as not. The deviation in
different cases may manifest itself under various
conditions, e.g., in near vision, on looking down,
under the influence of any strong emotion such
as fear or anger, when the patient is tired, &c.
Most frequently no immediate exciting cause can
be assigned. Occasional squints are sometimes
called periodic. I have notes of a few cases
which may properly be called periodic squints,
in which the deviation has appeared every
alternate day as regularly as a tertian ague.
(a) Premonitory occasional squints are simply
the precursors of constant squints. They usually
become constant after about two or three months.
(b) True occasional squints are much less
common than the premonitory variety. A true
occasional squint may gradually cease to show
itself as the fusion sense develops, or perhaps
optical correction of any refractive error may
relieve the condition, or it may maintain its
character unchanged throughout life. Many of
these last are not squints at all, in the strict sense
of the word, but are examples of esophoria, the
pathology and treatment of which are described
in chapter xi.
(2) In a case of constant unilateral squint the
deviation is constantly present, though the angle
may vary ; and it is always manifested by the
30 CONVERGENT SQUINT
same eye, when both eyes are uncovered. When
the " fixing eye " is screened, it turns in towards
the nose, and the "squinting eye," instead, is
directed to the object which engages the atten-
tion (unless this eye has lost the power of central
fixation). When the screen is removed, the fixing
eye immediately recovers itself, and the squinting-
eye again turns in.
(3) Alternating squint. — When a squinter fixes
with either eye indifferently, without covering the
other, the squint is said to alternate. Of all con-
stant squints, about 85 per cent, are unilateral
and 15 per cent, are alternating. These alterna-
ting cases arrange themselves into two distinct
classes — (a) Squints which accidentally alternate,
because the refraction is about the same in each
eye, do not essentially differ from unilateral
squints. In fact, if these cases are untreated,
usually one eye gradually comes to be used ex-
clusively for fixation, and the squint becomes
unilateral.
[p) In a case of essentially alternating squint
there is usually little or no refractive error, and
the visual acuity of each eye separately is, as
a rule, perfect. But these patients have a con-
genital total inability to acquire fusion. Alter-
nating squinters suffer much less than unilateral
squinters from neglect, because each eye is used
in turn, so that the vision does not deteriorate.
If the wearing of glasses does not cause the
CONVERGENT SQUINT 3 [
abnormal convergence to disappear (it seldom
does), an accurately performed operation will
remove the deformity. But the total absence
of the fusion sense renders a perfect cure of an
essentially alternating squint impossible.
Suppression of the vision of the deviating eye. —
In a case of convergent squint, as the two eyes
are not directed towards the same object, it might
be thought that everything would be seen double.
This is not so, however, save in the exceptional
instances referred to below. The visual acuity
of the deviating eye may be perfect, but the
picture formed in this eye is mentally ignored or
" suppressed," the attention being directed solely
to that formed in the fixing eye. This "sup-
pression " is not a voluntary act. The inability
to receive impressions from both eyes simul-
taneously is due to the defect of the fusion
faculty, which was the essential factor in. allow-
ing the squint to occur in the first instance.
This suppression, however, does not always
extend over the whole field of vision of the
squinting eye. If the deviation is of only slight
degree, there is a small part of the temporal side
of the field of vision of the squinting eye which
lies beyond the limit of the field of the fixing
eye. In this small area moving objects are
perceived by the squinting eye, but, as a rule,
are not accurately located. Thus, in an old case
of convergent squint, in which the deviating eye
32 CONVERGENT SQUINT
has lost the. power of central fixation, the extreme
nasal side of the retina of this eye (corresponding
to the extreme temporal side of its field of vision)
is the only part which is ever exercised. For
this reason, if the fixing eye in such a case be
covered, and the patient be told to look at a light
with the deviating eye, this eye will be seen to
roll still further inwards, in order to receive the
image of the light on the nasal side of the
periphery of the retina.
Occasionally one meets with a squinter who
has diplopia of a faint, unobtrusive kind. Squin-
ters never complain of diplopia as a trouble, but
one now and then meets with a child who, on
being carefully questioned, admits seeing a second
image. If the white handle of an ophthalmoscope
be held up, such a child will point to the real
handle and also to "the sham one," showing that
he really has a faint homonymous diplopia,
though, in the great majority of cases, he has
never mentioned it before. In such a case he
evidently has some trace of a fusion faculty, but
not sufficiently well developed to prevent the
occurrence of a deviation.
Diplopia artificially produced. — In a case of
unilateral or accidentally alternating squint, if
the deviating eye be not too blind, diplopia may
usually be induced by artificial means. For
instance, let the patient's attention be directed
to a candle flame. Place in a spectacle frame
CONVERGENT SQUINT $$
a red glass before one eye and a green glass
before the other. The images of the candle
flame, formed in the two eyes, being thus dif-
ferently coloured, the patient is often enabled to
perceive them both simultaneously.
Nature of diplopia. — The popular idea is that
a squinter sees the object which lies in the axis
of the deviating eye as well as that which lies in
the axis of the "straight" eye, so that he can
keep an eye on two places at once. Even in
the case of the very few squinters who are able
to see double spontaneously, or of those who are
enabled to do so by artificial means, this view is
not correct. A squinter who suffers from diplopia
sees, with his deviating eye, a faint, eccentrically-
placed image of the object to which the fixing
eye is directed, and suppresses the image of the
object which lies in the axis of the deviating
leye. In other words, he does not see two different
[objects, but sees two images of the same object.
The direction in space in which this second
image is mentally projected is peculiar.
Now, in a case of paralysis of, say, the right
external rectus muscle, if the right eye deviates
inwards to the extent of 20 , everything seen
with this eye will appear to be exactly 20 more
to the right than it really is ; in other words,
there is homonymous diplopia of 20 . If an eye
turns out to the extent of 20 owing to paralysis,
there is crossed diplopia of exactly 20 . The
34 CONVERGENT SQUINT
mind entirely ignores the faulty position of the
eye, and projects everything rigidly as though
the eye were straight. In a case of convergent
squint, on the other hand, if there is diplopia this
does not necessarily correspond in degree with
the angle of the deviation of the eye. The
eccentrically-formed image is, in any case, very
faint. Even the most intelligent patient usually
is unable to describe its position exactly, as the
angle of the diplopia seems to vary without any
corresponding variation in the angle of the squint.
In most cases the false image is placed about
half-way between the true position of the object
and the position which would correspond to the
angle of the squint. It would seem as though
the mind, being informed by the straight eye of
the true position of the object, were continually
trying to reconcile this knowledge with the
impressions produced by the eccentrically-placed
false image.
The amblyopia of convergent squint. — When a
patient first comes under observation after having
suffered from unilateral squint for a considerable
time, one usually finds that the deviating eye
is more or less blind, so blind sometimes that
fingers can scarcely be counted close to the face.
This amblyopia is sometimes, to a certain extent,
congenital. But by far the greater part of it is
due to a gradual loss of function in an eye which
is never used. It might have been prevented.
CONVERGENT SQUINT 35
This is plainly seen by comparing the vision in
my cases which came under treatment soon after
the first appearance of the squint, with the vision
in the cases which I saw for the first time only
after years of neglect or inefficient treatment (see
pages 76 and Jj).
The power of central fixation in the deviating
eye. — In a case of unilateral convergent squint,
if the fixing eye be covered the vision of the
(previously) deviating eye temporarily ceases to
be suppressed. In a fairly recent case, this eye
is then directed so as to receive, upon its macula
lutea, the image of the object looked at. But if
the case be long neglected, this sensitive central
region of the retina suffers much more from
disuse than the paracentral zone, while the peri-
pheral region suffers very little, if at all. As the
blindness progresses in this disused eye, a stage
is at length reached when the visual acuity of the
central region falls below that of the paracentral
zone, and later, even below that of the periphery
of the retina. If the fixing eye be now covered,
the deviating eye is not directed so as to receive
upon its macula the image of the object which
engages the attention, because the macula has
ceased to be the most sensitive part of the retina.
This eye then wanders, without remaining steadily
in any definite position (lost fixation). Or it may
fix with some part of the paracentral region, or
roll still further in towards the nose so as to
36 CONVERGENT SQUINT
present the extreme nasal periphery of the retina
for the purpose {false fixation).
False macula. —False fixation is, unfortunately,
exceedingly common in neglected cases of uni-
lateral squint. But the variety known as false
macula is rare. In an old case of squint, in which
the angle of the deviation has remained exactly
the same for several years, and in which the sup-
pression of the vision of the deviating eye is not
profound, the mind sometimes learns to make full
allowance for the faulty position of this eye. So
that the eccentric image, formed in the deviating
eye, is mentally projected to the same spot as
the true macular image, formed in the normally-
directed eye, and is blended with it. This false
macula is merely a small area which has escaped
the loss of function which has overtaken the sur-
rounding part of the retina. The visual acuity
of a false macula is never greater than the
normal visual acuity of the region in which it
is situated. I have rarely found it equal to ,.'■, ;
never greater. Many of these patients can pass
Hering's drop test. If an eye, with false macula
in a position of convergence, be put " straight "
by operation, crossed diplopia is produced. This
usually passes off within a few days, but occa-
sionally it persists for many months.
Monocula diplopia. — In an eye with " false
macula," central fixation has nearly always been
lost. Occasionally it is preserved. In such a
CONVERGENT SQUINT T>7
case, if the fixing eye be covered, the deviating
eye will immediately take up central fixation.
The " false macula" is then, as a rule, suppressed.
If it is not, the result is monocular diplopia. This
condition is exceedingly rare. In my detailed
notes of more than two thousand cases of squint
of all kinds, I find monocular diplopia only men-
tioned four times, although I have been constantly
looking out for this anomaly.
Apparent vertical deviation. — On applying the
mirror test in a case of convergent squint, one
not infrequently notices a slight upward deviation
also : then, on covering the originally fixing eye,
and causing the originally deviating eye to fix,
one sees that the originally fixing eye also turns
up as well as in. If the wearing of glasses causes
the convergence to diminish, the vertical devia-
tion will also diminish proportionately. In the
great majority of cases the vertical deviation
increases when the gaze is directed towards the
side of the fixing eye and diminishes or disap-
pears when the gaze is directed away from the
side of the fixing eye.
In some cases of divergent squint, the diver-
gent eye turns a little down also, no matter which
eye may be fixing.
A possible explanation is that in these cases the
planes of adversion and abversion of the two eyes,
instead of being horizontal, are titled down and out
towards each temple. Then, when the fixing eye is
4
38 CONVERGENT SQUINT
moved horizontally, the deviating eye, in making a
corresponding conjugate movement uncontrolled by
the fusion sense, moves in this titled plane. Take, for
example, a case of convergent squint 20 , exhibiting
this double upward deviation. Really each eye is con-
vergent io°, but the eyes have made a conjugate move-
ment of io° towards the side of the fixing eye so as to
bring this eye " straight " and double the apparent
convergence of the deviating eye. The fixing eye has
thus travelled out and down in its plane, and the
deviating eye has travelled in and up. A further conju-
gate movement towards the side of the fixing eye will
increase the difference in vertical height. A conjugate
movement away from the side of the fixing eye, by
bringing the eyes to corresponding points in their
respective planes of rotation, will cause the vertical
difference to lessen or disappear.
True vertical deviation. — In some cases of
squint there is a true vertical deviation, one eye
turning up when it becomes the deviating eye,
and the other eye turning down when it, in turn,
is made to deviate.
Spurious squint of infants. — During the first
few months of life, before the fusion faculty has
made much progress in development, it frequently
happens that the eyes converge for a few seconds
or a minute at a time, in response to some gastric
or other disturbance, Or, as nurses are wont to
express it, " Babies squint when they have the
wind." This is of no importance. Sometimes,
too, a child, whose fusion faculty is developing
quite normally in other respects, acquires this
faculty rather later than usual, just as a perfectly
CONVERGENT SQUINT 39
healthy, intelligent child may be late in learning
to talk. One may then see one or other eye
turn in, occasionally, for a minute or two at a
time, even when the child is old enough to walk.
Later, if the fusion faculty developes normally, it
will so control the movements of the eyes as to
prevent any recurrence of the deviation.
But if the child "crosses his eyes" for many
minutes at a time, or if one eye converges while
the other steadily fixes some object, or, more
especially, if the deviation is always manifested by
the same eye, the case is probably one of true
squint and demands investigation without delay.
And, under any circumstances, it is safer to
investigate any case in which a child is seen to
cross his eyes occasionally, rather than wait until
what may have been a premonitory occasional
squint becomes a constant squint.
" Growing out of a squint!' — With the advent
of puberty, the angle of a convergent squint often
tends to become somewhat less without any treat-
ment. In rather rare instances the eyes become
straight, or nearly so, and the patient is said to
have "grown out of the squint." But, in the
case of a unilateral squint, the squinting eye has
nearly always by this time become very blind
from disuse.
The belief in the spontaneous cure of squint is
very wide-spread among the general public. This
may be due partly to the fact that the deformity
40 CONVERGENT SQUINT
of squint does, in a few cases, disappear spontane-
ously as just mentioned, and partly to the fact
that an occasional squint is seen at one time and
not at another, but chiefly, I think, to the fact
that the spurious squint of infants ceases to
manifest itself when the fusion sense developes.
But, unfortunately, this superstition is not
entirely confined to the laity. I have often had
a child brought to me with the squinting eye
nearly blind from neglect, and have been told
that the family practitioner was consulted about
it years ago and that he advised the parents to
" wait to see if the child would grow out of the
squint."
General course of an untreated case of constant
unilateral convergent squint. — At the first ap-
pearance of a deviation, the squinting eye always
has the power of central fixation when the fixing
eye is covered, and the vision is nearly always
good in both eyes. There is rarely some con-
genital amblyopia. This congenital amblyopia
is far less frequent than is generally supposed,
and is never responsible for the extreme blindness
so often found in old neglected cases of squint.
In an untreated case, the vision of the deviating
eye, being entirely suppressed, gradually deterio-
rates from disuse, until, in many cases, central
fixation is lost, and the vision reduced to the
counting of fingers close to the face. The
younger the child the more readily does this
CONVERGENT SQUINT 4 I
amblyopia from disuse occur. So much so that
it is commonly believed, even by ophthalmic
surgeons, that an eye which begins to squint in
early infancy is necessarily very blind, and this
blindness is supposed to be congenital. Yet this
is not the case. Of the cases which came under
my care soon after the first appearance of the
deviation I do not find the young squinters
especially amblyopic (see chapter v.).
The deviation, in an untreated case of con-
vergent squint, usually increases in degree up
to the time of puberty. After this time it often
tends to become gradually less, until about forty
years of age, when in some cases it is scarcely
noticeable. It is not very uncommon to see a
middle-aged patient with an inconspicuous squint
of perhaps two or three degrees, and a nearly-
blind eye. He usually says he squinted when he
was a boy, but gradually grew out of it.
The fusion sense, of course, cannot be developed
during the continuance of a deviation, except by
artificial means (e.g., exercises with the amblyo-
scope). If it be prevented from developing in
infancy and early childhood, it will never develop
at all to any useful extent. It is true that
binocular vision of a sort may, in exceptional
cases, be acquired as late as eight or nine years
of age, but it is so feeble that it is powerless to
maintain the normal relative direction of the eyes
in the presence of uncorrected hypermetropia ;
4 2
CONVERGENT SQUINT
so that glasses must be worn throughout life to
prevent a return of the deviation.
Age at which the deviation first appears. — I n
my note-books I find the onset-age recorded in
1,017 cases of unilateral convergent squint, and
in 178 alternating cases.
The number of unilateral cases beginning in
each year of life was as follows : —
Before 1 year
... 134 cases
Between 1 and 2 years ...
... 186 „
2 „ 3 „
... 247
» 3 „ 4 »
... 189 „
„ 4 „ 5 „
... 113
» 5 „ 6 ,
■ •■ 73 ,,
After 6 years
... 75 »
It will be seen that in nearly 75 per cent, of
the cases the deviation appeared before the end
of the fourth year, and in less than 7 h per cent,
its advent was delayed until after the sixth year.
The alternating cases work out as follows : —
Before 1 year
.. 61 cases
Between 1 and 2 years
-• 34 „
2 „ 3 »
23 „
3 „ 4 »
•• 29 „
4 „ 5 »
• • n »
„ 5 ,. 6 »
•• 6 »
After 6 years
■• 14 „
In more than 53 per cent, of these alternating
cases the deviation was seen before the end of the
second year. This high proportion is due to the
fact that the essentially alternating squints appear
in early infancy.
CONVERGENT SQUINT 43
Refractive error in cases of convergent squint. —
In infancy and early childhood hypermetropia is
the normal refractive condition, myopia or even
emmetropia being then very uncommon. In the
absence of the controlling influence of the fusion
sense, the state of the refraction is the main factor
in determining whether the eyes shall deviate
inwards or outwards (see chapter iv.). It is not
surprising, therefore, that convergent squinters
are nearly always hypermetropic, and very fre-
quently suffer from hypermetropic astigmatism
also.
I have notes of 1,636 cases of convergent
squint which are available for the present
enquiry.
In twenty-three of these cases, or about \\
per cent., both eyes were myopic. I have not
included these in the subjoined tables.
I have arranged the 1,384 cases of unilateral
convergent squint in groups, according to the
number of dioptres of hypermetropia in the
lowest meridian of the fixing eye.
I have calculated the average refractive error
in the highest and in the lowest meridian of
each eye. In about three-fourths of these cases
the age at which the squint was first seen was
recorded on the case sheets. The table shows
the number of cases found in each group, and
the average onset-age.
The 229 cases of alternating convergent squint
44
CONVERGENT SQUINT
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CONVERGENT SQUINT 45
are similarly tabulated, except that they are
arranged in groups according to the number of
dioptres of hypermetropia in the right eye.
Astigmatism in unt 'lateral convergent squint.
—In the 1,384 cases I found the proportion of
astigmatic to non-astigmatic eyes to be as
follows : —
Fixing eyes. Deviating eyes.
No astigmatism ... 561 4 QI
Astigmatism ... 823 983
But a very large proportion of people whose
eyes are, for all practical purposes, normal, have
at least half a dioptre of astigmatism. It would
only be misleading to expect the eyes of squinters
to conform to a higher standard than those of
normal-sighted people. If we disregard astig-
matism which does not exceed 0*5 d, we get
the following results : —
Fixing eyes. Deviating eyes.
Astigmatism not over 0.5 D 836 628
Astigmatism over 0-5 D ... 547 75 6
On comparing the degree of refractive error
in the two eyes in each of the 1,384 unilateral
cases we find : —
Isometropia 4-7 cases.
Anisometropia 957 cases.
Or, disregarding differences which do not
exceed 0*5 d —
Anisometropia not exceeding 05 D 663 cases.
Anisometropia exceeding o"5 D 721 cases.
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CONVERGENT SQUINT
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CONVERGENT SQUINT 47
These alternating cases show a much lower
percentage of astigmatic eyes than the unilateral
cases : —
Right eye. Left eye.
No astigmatism 114 II2
Astigmatism "5 "7
If we disregard astigmatism which does not
exceed 0*5 d, we find : —
Right eye. Left eve.
Astigmatism not over 0-5 D 14° J 4 X
Astigmatism exceeding 0-5 d ... 89 88
A comparison of the refraction of the two eyes
in each of the 229 alternating cases shows : —
Isometropia 13 1 cases.
Anisometropia 98 cases.
Or, disregarding differences which do not
exceed 0*5 d : —
Anisometropia not exceeding o - 5 D 185 cases.
Anisometropia exceeding o - 5 D 44 cases.
The relative frequency of squint was the subject
of a careful enquiry which Mr. R. E. Hanson,
oculist to the Education Department of the
London County Council, has been kind enough
to undertake at my request. During the last two
years 10,239 school children have been examined
in the Marylebone and the Tower Hamlets dis-
tricts. 253 of these children exhibited a constant
squint. In 231 of the cases the squint was con-
vergent, and in 22 cases divergent. The test
used was the mirror test described on page 80.
4 8
CHAPTER IV.
THE .ETIOLOGY OF CONVERGENT SQUINT.
/Many curious suggestions have, in former
times, been made as to the cause of squint, such
as " an evil disposition," naughtiness, imitating
other members of the family who squint, the
habit of turning the eye to look at a curl or
ribbon on one side of the face, &c. The first
definite theory, which was almost universally
accepted, attributed convergent squint to a
shortening of the internal recti. The natural
corollary of this was that the affection might
be cured by dividing these muscles or their
tendons. The theory and its practical applica-
tion seemed so plausible and simple that an age
of indiscriminate muscle-cutting ensued. When
the disastrous results of this practice were begin-
ning to be recognised, Donders published his
great work, and his "accommodation theory" of
the cause of squint immediately came into vogue.
It will be well to examine these two theories
n detail.
uscle theory. — Many writers on convergent
squint have attributed the anomaly to an undue
THE /ETIOLOGY OF CONVERGENT SQUINT 49
shortness or tightness of the internal recti, to a
faulty insertion of the tendons of these muscles,
or to a paresis of the external recti. To an
observer who sees in a case of convergent squint
only its most obvious symptom, viz., the abnormal
convergence, it may seem reasonable to attribute
this deformity to a defect of the muscles which
move the eyes. A little investigation ought to
convince anyone of the falsity of this view.
Of 1,523 cases of convergent squint in which
I investigated this point, I found the power of
abversion (outward rotation) of each eye tested
separately to be quite perfect in 81 per cent. ;
in the remaining 19 per cent, the power of
abversion was sub-normal, but the defect in most
of these 19 per cent, was slight. This alone
would seem sufficient to demonstrate that, in 81
per cent, of convergent squints at least, there is
no undue shortness of the internal recti or paresis
of the external recti muscles. In the 19 per cent,
the deviation had, in the vast majority of cases,
lasted several years, and the average degree of
the defect of abversion was directly proportionate
to the duration of the deviation. The defect of
abversion in nearly all the 19 per cent, of cases
would therefore appear to be due to secondary
changes in the muscles and fascia;, the result
of the long continuance of the deviation, not its
cause. One wonders that these secondary changes
take place so seldom and to such a slight extent.
50 THE /ETIOLOGY OF CONVERGENT SQUINT
It is a matter of common observation that a
convergent squint very frequently disappears, or
the eyes even diverge, during general anaesthesia.
Occasionally a very high degree of convergence
disappears when the accommodation is paralysed
by atropine. It always reappears when the effect
of the atropine has passed off.
Of cases of convergent squint which are treated
with glasses alone, in about 30 per cent. 1 the eyes
eventually become approximately "straight," and
remain so as long as the glasses are worn.
These facts scarcely seem compatible with a
muscular origin of squint.
Bonders theory. — When a person with normal
emmetropic eyes looks at an infinitely distant
object, such as a star, the visual axes are parallel,
and the static refraction of each eye is sufficient
to focus the image of the object on its retina. If
the person now looks at an object only a foot
away from him he must turn the eyes slightly
inwards (convergence), in order that both visual
1 1 have no statistics of my own showing the proportion
of " cures " effected by glasses alone, because I do not rely
solely upon optical correction and operation. Of ninety-
four cases of unilateral convergent squint quoted by
Holthouse, the deviation was gradually overcome, and the
eyes remained " straight " so long as glasses were worn in
twenty-nine cases, or 308 per cent. Lang and Barrett
(R.L.O.H. Reports, vol. xii.) had thirty-seven cures by
glasses out of 102 cases, or 36-3 per cent. But in this
series all cases in which less than five degrees deviation
remained were considered cured.
THE ^ETIOLOGY OF CONVERGENT SQUINT 5 I
axes may meet at the object. At the same time
each eye must be focussed for near vision (accom-
modation), in order that the object may be seen
distinctly. These two acts, accommodation and
convergence, being always performed together,
have become " associated " by hereditary habit,
so that it is difficult to converge without accom-
modating or to accommodate without converging.
Hypermetropic eyes in a state of rest are out
of focus even for distant objects, and still more so
for near objects. A hypermetrope, therefore, in
order to see distinctly, must accommodate in
distant vision to a degree corresponding to the
amount of his hypermetropia. In near vision he
must accommodate both for the hypermetropia
and for the nearness of the object. There is a
tendency for a proportionate abnormal conver-
gence to be associated with this abnormal effort
of accommodation. Donders considered this
tendency to be the cause of convergent squint,
and he advised optical correction of the hyper-
metropia with a view to curing the squint.
By this chain of observation and reasoning the
great physiologist let the first ray of light into
this dark corner of ophthalmology, and gave the
first indication for a rational treatment of con-
vergent squint. But he was mistaken in sup-
posing hypermetropia to be the fundamental
cause of the malady.
The vast majority of children are hyper-
52 THE .-ETIOLOGY OF CONVERGENT SQUINT
metropic. Of these hypermetropes only a small
percentage present themselves at the clinics,
whereas nearly all the squinters come at some
time or other. Yet, even there, one sees at least
a dozen hypermetropes who do not squint for
one who does. This cannot be explained on the
hypothesis that the severe cases of hypermetropia
especially tend to cause squint, because statistics
show that this is not the case (see tables i. and
ii., chapter iii.).
It is usually stated that moderate degrees of
hypermetropia are especially prone to be asso-
ciated with squint. This is explained by saying
that a child with moderate hypermetropia will
accommodate in order to see distinctly. He
only manages to make the extra accommodative
effort by bringing into play also an associated
effort of convergence. So that he sees distinctly
with one eye and turns in the other. But, it is
said, if the hypermetropia be excessive, he will
not be able to accommodate sufficiently, so that
he gives up the struggle, and neither sees dis-
tinctly nor squints.
But this ingenious argument is based on false
premises. Moderate degrees of hypermetropia
are more common than high degrees, not only
in those who squint, but also in those who do
not squint. I looked through my out-patient
letters at the West Ham Hospital for about
eighteen months, and tabulated all the cases
THE ETIOLOGY OF CONVERGENT SQUINT 53
of hypermetropia, without squint, in which the
refractive error was measured by retinoscopy
under atropine. I tabulated the cases according
to the degree of hypermetropia, and worked out
the percentage number of eyes in each grade. 1
The results, in the cases in which the hyper-
metropia was more than 2 d, were found to
correspond very closely with my squint statistics
treated in the same way. The proportion of
cases with less than 2 d was lower among the
non-squinters than among the squinters. Also
the average degrees of astigmatism were higher
among the non-squinters than among the squin-
ters. This is evidently due to the fact that most
of the non-squinters were patients who sought
advice on account of headaches or visual defect.
It will thus be seen that the degree of the
refractive error has very little to do with the
question of whether the patient shall or shall not
squint in the first instance, though, of course,
when the squint is once established, the refractive
error becomes a very important factor.
A high degree of hypermetropia has no in-
1 In cases in which there was also astigmatism, the
mean between the highest and lowest meridian was taken.
I have since compared the results of taking the highest
meridian only, also the lowest meridian only. The number
of cases taken excludes any accidental source of error. A
slight defect in this mode of comparison will, of course,
suggest itself, but the error is not sufficiently grave to
affect the main results.
54 THE /ETIOLOGY OF CONVERGENT SQUINT
fluence in determining an early onset of squint,
as is conclusively shown by the following table.
In the unilateral cases I have taken the average
of the highest and lowest meridian in the fixing
eye, and in the alternating cases I have taken
the average of both eyes.
Less than +2 D average age of onset = 2^47 years. 1
+ 2 D to +4 D „ „ „ = 2-85 „
+4 D to +6 D „ „ „ = 2-92 „
More than +6 D „ „ „ = - 2*96 „
A great many children who suffer from con-
vergent squint have no more than the normal
degree of hypermetropia, while 1 or 2 per cent,
are actually myopic.
It is evident, then, that, though hypermetropia
stands in some close setiological relation to con-
vergent squint, it is not the essential cause of the
anomaly.
/Etiology of Convergent Squint.
For the sake of clearness, I will first state my
proposition, and give the proofs afterwards.
In a case of convergent squint there is, in
addition to the most obvious symptom, the de-
formity, always a defect of the fusion faculty, and
there is nearly always a suppression of the vision
of the deviating eye.
j
1 The average age of onset is low in these squinters, with
less than 2 d of hypermetropia, because cases of essen-
tially alternating squint are included in this table.
THE /ETIOLOGY OF CONVERGENT SQUINT 55
In the human infant, the motor coordinations
of the eyes are already partially developed at
birth. During the first few months of life these
serve (in the absence of any disturbing' influence)
to maintain approximately the normal relative
directions of the eyes. Soon the fusion faculty
begins to develope. I have found distinct evi-
dence of binocular vision in the sixth month.
Normally the development of the fusion faculty
is well-advanced by the twelfth month, and com-
plete before the end of the sixth year. When the
fusion faculty has begun to develope, the instinctive
tendency to blend the images formed in the two
eyes — -the "desire for binocular vision," as it is
called — will keep the eyes " straight." When the
fusion faculty is fairly well developed, neither
hypermetropia, nor anisometropia, nor hetero-
phoria can cause squint. In fact, then, nothing
but an actual muscular paralysis can cause an
eye to deviate, in which case the resulting diplopia
is intolerable. Sometimes, however, owing to a
congenital defect, the fusion faculty developes
later than it should, or it developes very imper-
fectly, or it may never develope at all. Then,
in this case, there is nothing but the motor
coordinations to preserve the normal relative
directions of the eyes, and anything which dis-
turbs the balance of these coordinations will
cause a permanent squint. Thus the essential
cause of squint is a defect of the fusion faculty.
' In the presence of this fundamental cause, the
eyes are in a state of unstable equilibrium, ready
to squint either inwards or outwards on slight
provocation. This provocation may be supplied
by:-
(i) Hypermetropia. — As already explained,
uncorrected hypermetropia causes a tendency to
abnormal dynamic convergence of the visual axes.
In the vast majority of cases of hypermetropia the
fusion sense is perfect, so that this tendency is
kept in check and the child does not squint. If,
however, the fusion sense is deficient, the eyes are
free to yield to this tendency, and a convergent
squint is established. In the cases in which
hypermetropia is the immediate exciting cause,
the abnormal convergence is at first entirely dyna-
mic, static convergence being nil. The squint
is at first occasional — when the child is looking
at nothing in particular, relaxing the accom-
modation, the deviation disappears. Optical cor-
rection of the refractive error at this period often
cures the deviation. But if nothing is done, the
excessive exercise of the function of dynamic con-
vergence causes an abnormal static convergence
to appear. So that the visual axes are convergent
even when the eyes are completely at rest. At
this period optical correction does not cause an
immediate disappearance of the deviation. It
may gradually do so, perhaps, after the glasses
have been worn for a few weeks or months.
THE /ETIOLOGY OF CONVERGENT SQUINT 57
In cases in which the fusion sense is present
but feeble, it may be strong enough to resist the
strain of uncorrected hypermetropia during in-
fancy, but may give way when the child's atten-
tion is directed to his first lessons. There is
scarcely ever diplopia. Rarely one meets with
a child who, when patiently questioned, admits
that he sees a second image. This faint diplopia
persists, but is never annoying.
During the first few weeks of life, even in cases
of very high hypermetropia, the motor coordina-
tions suffice to maintain approximately the normal
relative directions of the eyes, until the developing
fusion faculty takes control and makes everything
safe. Probably the infant does not use his ac-
commodation much at this early period. But, in
rare instances, hypermetropia may cause a squint
before the period at which the child should
normally begin to acquire the fusion faculty {e.g.,
Case A, 503, page 151). In such a case, if the
deviation is allowed to persist, the natural de-
velopment of the fusion faculty will, of course,
be prevented.
(2) Anisometropia, and the rare congenital
amblyopia, predispose to squint by making bin-
ocular vision more difficult. One occasionally sees
a case of squint in which the fixing eye is approxi-
mately emmetropic and the deviating eye has
perhaps 10 or 15 d of myopia.
(3) If the fusion sense be perfect, a want of
58 THE /ETIOLOGY OF CONVERGENT SQUINT
balance of the motor apparatus of the eyes will
cause heterophoria but not squint. But in the
absence of the controlling influence of the fusion
sense, this motor imbalance is free to cause an
actual deviation. This is seen when, in examin-
ing a case of heterophoria, fusion is temporarily
rendered impossible by means of Maddox rod,
coloured glasses, &c.
(4) Specific fevers, especially whooping cough,
are often assigned by the parents as the cause of
the squint. One usually hears that the child was
seen to squint during convalescence, that the
squint was, at first, occasional, and that it became
constant after a few weeks. These children
usually have a good deal of hypermetropia. The
mode of origin of these squints is probably as
follows:— The fusion sense is defective (shown
by the absence of diplopia), but the motor co-
ordination, or some slight degree of fusion sense,
has hitherto sufficed to prevent the occurrence of
a deviation. During convalescence the child is
given picture-books. Owing to the muscular
enfeeblement caused by his illness, he is unable
to accommodate so well as formerly. The exces-
sive effort of accommodation upsets the unstable-
equilibrium. At first^the abnormal convergence
is dynamic only, and disappears when the child
relaxes his accommodation. A pair of spectacles
at this period often brings about a cure. Hut if
he opportunity be lost a static convergence
THE ^ETIOLOGY OF CONVERGENT SQUINT 59
appears, and what was merely a premonitory
occasional squint becomes constant.
As a contrast to these cases, it occasionally happens
that a child, whose fusion faculty is perfect, suffers
from a paresis of an external ocular muscle after
diphtheria. The child complains of persistent and
annoying diplopia until the muscle recovers its func-
tion. I recently had the opportunity of watching such
a case. The patient, a little girl, aged five years, had
paresis of the right external rectus muscle after
diphtheria. She volunteered the statement that she
saw "two nurses" and that "things looked funny."
She was uncertain in her movements in running about,
and often made a false shot in picking up a ball
from the floor. When I gave her a picture book to
look at, she covered the affected eye with her hand.
When I saw her a few days later, she kept her head
constantly turned to the right, evidently to enable her
to blend the images. The case completely recovered
in about seven weeks.
(6) Violent mental disturbance, caused by severe
fright, " convulsion-fits," &c, may, in the absence
of the fusion faculty, upset the equilibrium of the
convergence centre. The convergence is static,
it appears immediately, and is constant from
the first. Refractive error is not an important
feature. A large percentage of these cases are
alternating.
Injury during birth. — Now and then one sees
a case in which the power of abversion of an
eye has been absent since earliest infancy,
probably owing to injury to the sixth cranial
nerve during birth. In most of these cases the
60 THE .ETIOLOGY OF CONVERGENT SQUINT
position of the eye prevents the natural develop-
ment of the fusion sense. If no precautions are
taken the eye may become extremely amblyopic.
Hereditary influence is a marked feature in any
series of cases of convergent squint. In 1,373
cases of squint in which I was able to get probably
reliable information, there was a history of squint
in parent, grand-parent, brother, or sister of the
patient in no less than 711, or 5 1 78 per cent.
Proof that the Essential Cause of Squint is a
Defect of the Fusion Faailty.
If a pair of object-slides such as fig. 17 be put
in the amblyoscope, a person with a normal pair
of eyes will be able to blend the two imperfect
images into one complete picture. If the angle of
the instrument be varied the eyes will converge,
or (to a certain extent) diverge also, in order to
follow the objects and maintain fusion.
Now take a young patient with an ordinary
unilateral convergent squint, and good vision in
each eye. Adjust the amblyoscope to suit the
angle of his deviation. He will only see with the
fixing eye, the vision of the squinting eye being
suppressed. If the suppression be now overcome
by the method described in chapter viii., he
will see the two imperfect images simultaneously.
After a little practice, a position can usually be
found in which the two imperfect images overlap,
so that the patient sees them blended into one
THE ETIOLOGY OF CONVERGENT SQUINT 6 1
complete picture. But they are blended only in
that one position. If the angle of the instrument
be again altered, the images at once separate —
no effort can be made to maintain fusion. This
shows that, though the fusion faculty is not
quite absent, it is exceedingly ill-developed. The
brilliant results obtained in these cases by train-
ing the fusion faculty at an early age, strongly
support the view that the defect of this faculty
was the fundamental factor in permitting the
deviation to occur.
Consider next a typical case of essentially
alternating squint. The visual acuity of each eye
is perfect ; there is no important refractive error ;
the movements of each eye separately are perfect.
Why then does such a pair of eyes squint ? The
muscle theory cannot explain it, because there is
no motor defect of either eye. Hypermetropia
cannot be the cause, because there is little or
no refractive error ; moreover, the wearing of
correcting glasses usually has no effect upon the
deviation. No theory hitherto put forward has
satisfactorily explained these cases. But, if the
condition of the fusion faculty be examined, the
mystery is cleared up at once. Let a patient with
an essentially alternating squint look at a pair of
object slides such as fig. 16 in the amblyoscope.
When the objects are very far apart, he may be
able to see both. But when they are made to
approach each other, he loses sight of one of them.
62 THE AETIOLOGY OF CONVERGENT SQUINT
No amount of practice will ever enable an essen-
tially alternating squinter to see the two devices
simultaneously when they are close together,
much less to blend them. There is a congenital
total absence of the fusion faculty.
The great frequency with which squint occurs
in more than one member of a family has enabled
me to obtain still more direct evidence. When I
have had a child under treatment for convergent
squint, I have, in very many instances, induced
the mother to bring me also for examination a
younger brother or sister of the patient, who had
not hitherto squinted. I examined the fusion
sense of all except the most intractable of these
brothers and sisters of squinters with the amblyo-
scope. I have been able to follow the subsequent
history of 157 of these children. In 106 cases I
found the fusion faculty well developed. Not one
of these has subsequently squinted. Of thirty-
seven cases in which the note was " doubtful,"
six have since squinted. Of fourteen cases in
which my note said " fusion faculty very defi-
cient," eight have since developed a constant
squint, and another child is said to cross her
eyes occasionally,
63
CHAPTER V.
AMBLYOPIA, CONGENITAL AND ACQUIRED.
The amblyopia discussed in this chapter is a
partial blindness of an eye in which the most
careful examination of the fundus and media
reveals nothing sufficient to account for the
defect. This amblyopia persists after accurate
optical correction of any refractive error which
may be present. It may be either congenital or
acquired.
It will be well to consider congenital ambly-
opia and the acquired form separately, before
discussing" the amblyopia so often found in cases
of convergent squint.
Congenital amblyopia, apart from squint, is very
seldom met with. One should not accept a case
as being one of congenital amblyopia, unless
careful questioning of intelligent and observant
parents makes it certain that the patient has
never squinted as a child.
In the course of examining the refraction of
many thousands of patients who have never
squinted, I have only met with twenty-three cases
of amblyopia, of ~ or higher, which I have felt
justified in regarding as congenital. These cases
64 AMBLYOPIA
are described in detail in the appendix (p. 219).
They have certain peculiarities in common. The
fundus and media are normal in appearance.
The fields of vision, both for white and colours,
are full. There is no scotoma. Central colour
perception is normal. The peripheral form vision,
up to within 20° of the fixation point, is normal. 1
So that the defect would seem to consist in a want
of due preponderance of the macular region,
and not in a general lowering of the sensibility
of the visual apparatus. In no case was the
vision of the amblyopic eye less than e G o- But
the most remarkable feature of these cases is that
the defect is confined to one eye, which almost
invariably has a high degree of compound hyper-
metropic astigmatism ; while the other eye has
normal vision, and either normal refraction or
hypermetropia, without any notable degree of
astigmatism." In many of the cases the fusion
faculty was examined with the amblyoscope. It
was found to be well developed.
1 For the purpose of testing the peripheral form vision,
I use three metal screens about two inches square, each
showing a white O on a black ground. The letters on the
three screens are of different sizes. By a simple mechanical
device the O is readily converted into a C. The screens
are successively attached to the object-carrier of a peri-
meter. The investigation is proceeded with just as in
mapping out the fields of vision, the patient being required
each time to say whether the letter is O or C. In this way
three zones are mapped out on the chart. This method
though very valuable for purposes of scientific investigation,
is too tedious for ordinary clinical use.
CONGENITAL AND ACQUIRED 65
There is another small group of cases in which
the amblyopia may almost certainly be regarded
as congenital. Table iii., p. 76, includes only cases
of squint in which my treatment was begun soon
after the first appearance of the deviation and
was carried out thoroughly, so that there was
scarcely a possibility of any acquired amblyopia.
It will be seen that the vast majority of these
patients have, with optical correction, perfect
vision in each eye. In seventeen cases out of
the 193 the vision of the squinting eye was f or
Y^. In nine cases it was ~ or A- In two cases
it was 3 6 g or £ - In no case was the vision lower
than <&, and in no case was the power of central
2 I wish to avoid vague speculation. But the thought
obviously occurs to one — Is it possible that, in some of
these cases in which I have regarded the amblyopia as
congenital, it may really have been acquired through the
patient's confining his attention to the sharp image, even
though this is fused with the blurred image of the astig-
matic eye ? The fact that the amblyopia is always confined
to one eye lends colour to the suggestion. The possibility
of confining one's attention to the image formed in one
eye, and yet, at the same time, exercising binocular vision,
is easily demonstrated. Let one imitate the refractive con-
dition of one of these patients by wearing a high cylin-
drical lens before one of one's own eyes, then read the test
types with both eyes open. By confining the attention
to the naked eye, one reads f. In reading a book one
soon learns to disregard entirely the blurred image seen
through the cylinder. At the same time, it is easy to
convince oneself that one is exercising binocular vision —
prism, base in, produces diplopia ; prism, base out, causes
convergence of the visual axes in order to blend images ;
four-dot test, &c.
66 AMBLYOPIA
fixation absent. On referring to my case books,
I find that, in the more amblyopic cases, the
defective eye nearly always had a high degree of
compound hypermetropic astigmatism, while the
other eye had perfect vision and nearly always
simple hypermetropia without any notable astig-
matism. These cases are described in the
appendix.
Amblyopia acquired from disuse (amblyopia
ex anopsia). In a case of convergent squint,
even though the vision of each eye separately be
perfect, the patient will, when both eyes are open,
only see with the " straight " eye. The impres-
sions received by the deviating eye are mentally
" suppressed." In the case of a young child with
a constant unilateral squint, the result of this
disuse of the deviating eye is that its visual acuity
gradually deteriorates. This deterioration from
disuse is the more rapid the younger the child, so
much so that it is commonly believed that an eye
which squints in infancy is necessarily very blind.
This is not so, as table iii. clearly shows. A
child with good vision in each eye, who developes
a constant unilateral squint at the age of six or
eight months, will, in the absence of proper treat-
ment, become rapidly blind in the squinting eye.
This loss of vision in the infant's deviating eye is
so rapid that the power of central fixation is often
lost within eight or ten weeks. In an eye which
begins to squint constantly at the age of, say,
CONGENITAL AND ACQUIRED 6j
eighteen months, the progress of the blindness is
rapid, but much less so than in a younger child.
At least five or six months usually elapse before
the eye loses the power of central fixation. An
eye which begins to deviate constantly at the age
of three years seldom quite loses the power of
central fixation in less than a year. I have never
seen central fixation lost in a case in which the
squint had first appeared after six years of age.
After six years of age amblyopia ex anopsia
seldom takes place to any great extent. Acquired
amblyopia is a true loss of vision, not a failure of
the function to develope, as is shown by cases
quoted below.
I have notes of several cases in which ignorant
or careless parents have accidentally performed
upon their children most instructive (but disas-
trous) experiments bearing upon this subject.
Here are brief notes of a few of the more striking
examples.
CASE A, 77. 1 — On November 14, 1895, I saw, at
West Ham, a girl, aged 2 years 7 months. She had
constant convergent squint R. E. 22 . The mother
1 The letters and numbers are the index marks of the
notes in my squint case-books. In the case notes I have
used certain abbreviations, some of which may require
explanation, e.g., " C.S.R.E. 22 " means "constant uni-
lateral convergent squint, the angle of deviation being 22°
in distant vision and the right being the deviating eye."
" V.R.E." means " vision of the right eye." After glasses
had been ordered, the angle of deviation and the visual
acuity were always measured with the glasses on.
68 AMBLYOPIA
said that the child had squinted about a month. The
squint was nearly alternating. After shading L. E. for
a moment, she would fix with R. E., and continue to
do so for a minute or two after removing the shade.
Two hours after putting a drop of atropine into the
L. E. she was seen to squint always with the L. E. and
fix with the R. E.
November 21, 1895. — Retinoscopy under atropine
each eye + 375 D sph. I ordered + 3 D sph. for
constant wear ; and a drop of liquor atropinae to be
put into the L. E. only every morning. Child to be
seen again in a month.
August 22, 1901. — The child is brought to me at the
West Ham Hospital. I have not seen her for nearly
six years. The mother has no recollection of having
used the drops for the L. E. She says the child wore
the glasses for about a year, then lost them. No
treatment since. Child is now aged 8 years 4 months.
She has convergent squint R. E. 17 . The fixation of
the R. E. is lost. Vision of the R. E. is reduced to the
counting of fingers at 5 feet.
Case D, 527. October 16, 1900. — Boy, aged 13
months, brought to Moorfields. The mother said he
had " squinted the last few weeks." Child has con-
vergent squint R. E. 30° about, varies slightly. Good
central fixation R. E.
October 23, 1900. — Retinoscopy under atropine shows
refractive error R. E. + 4 D sph. + 1 D cyl. ax. vert.,
L. E. + 4 D sph. Ordered glasses 0*5 D less than the
retinoscopy. Ordered guttaj atropine 1 per cent. L. E.
only every morning.
December 4, 1900. — Child uses unatropised R. E.
always, both in near and distant vision, and squints
with atropised L. E. Ordered, stop the drops and
come again in a month.
January 8, 1901. — Child has now convergent squint.
18 with the glasses. The squint alternates. Ordered,
wear glasses and come first week in April.
CONGENITAL AND ACQUIRED 69
January 3, 1902. — Child has not been seen for a year.
Soon after last visit mother says he lost his glasses.
He has had no treatment since. There is now con-
vergent squint R. E. 32 . R. E. has lost the power of
central fixation. With L. E. bandaged, child sees the
1^ inch ivory ball when it is rolling on the floor, but can-
not find it when stationary, unless it is close to his feet.
Case A, 432. January 11, 1900. — Boy, aged 2 years
2 months, was brought to me at West Ham Hospital.
He had alternating convergent squint 27 . Squinted
more in near vision. Mother said he had squinted less
than a month. I ordered ung. atrophias thrice daily,
for both eyes, and told the mother to bring him again
in a week to have his eyes tested for glasses.
November j, 1901 (one year and ten months later).
— The mother did not use the ointment and come
again as directed, as the child's father " did not believe
in having the eyes messed about with." Child now
has convergent squint L. E. 34 . L. E. has lost the
power of central fixation, and the ivory-ball test shows
Case D, 730. July 13, 1901. — Girl, aged 7 weeks,
has convergent squint R. E. io° approximately, angle
varies slightly. Good central fixation R. E.
July 17. — Retinoscopy under atropine, each eye +
2*5 D sph. Ordered, ung. atropine for L. E. only,
every morning.
July 51. — Child uses R. E. (unatropised) almost as
often as L. E. (atropised). Ordered, continue atropine
L. E. only.
August 28. — Atropine has not been used. R. E. now
converges 30 about, fairly constant in degree. R. E.
has lost the power of central fixation. Ordered, con-
tinuous occlusion L. E. for three days.
August 31. — No fixation R. E.
1 did not care to order continuous occlusion of this
JO AMBLYOPIA
very young infant's better eye for many weeks, for fear
of rendering it amblyopic. I therefore ordered the eye
to be bandaged half of each day. In six weeks R. E.
had regained steady central fixation.
Case B, 24. February 4, 1896.— I was asked to see
a girl aged 2 years 10 months. L. E. had squinted
occasionally since she had whooping cough, aged i\
years, but for the last four or five weeks the squint
had been constant. Angle of convergence 26 . After
instilling atropine into E. E. only for about an hour,
she turned in R. E. and used L. E. always, both in
near and distant vision. She could easily see a small
marble at the other end of the room with L. E. The
sight of this L. E. must have been perfect or nearly so.
A week later, retinoscopy under atropine. — R. E. +
4-5 D, L. E. 4- 5*5 D.
I ordered spectacles for constant wear, R. E. + 4 d
sph., L. E. 4- 5 U sph. I also ordered a drop of
atropine to be put in R. E. only every morning, and
proposed exercises with the amblyoscope in a few
weeks.
The parents, not being favourably impressed by my
methods, determined to have " another opinion."
The child was taken to an ophthalmic surgeon who
said she was too young for glasses. He ordered atro-
pine for both eyes twice daily. This was kept up for
rather more than a year, after which she was given
spectacles. At the age of 7 years the surgeon operated
on the left eye (tenotomy).
December 17, 1901. — The child was brought to me
live years and ten months after 1 saw her first. She
had convergence of L. E. 14", while wearing her glasses.
L. E. was prominent and caruncle sunk. The L. E.
had lost the power of central fixation, ami its vision
was reduced to the counting of fingers at one foot from
the face. 1 have since removed the deformity by
advancement of the left external rectus, but the eye
oi course remains hopelessly blind.
CONGENITAL AND ACQUIRED 7 I
Case B, 83. October 27, 1897.— A girl, aged 2 years,
was brought to me. The mother said she had squinted
occasionally for several months, but she had squinted
constantly since a few days before the August bank
holiday. She had convergent squint L. E. 21°. Using
R. E. she could always see the half-inch ivory ball at
the far end of the (22 feet) room. When R. E. was
bandaged she could see the 1^ inch ball with the L. E.,
but she had great difficulty in finding the 1 inch ball
unless she was allowed to begin to run after it before
it had stopped rolling.
November 1, 1897. — Retinoscopy under atropine
shows error of refraction to be, each eye + 3*5 D sph.
+ 075 D cyl. ax. vert. Ordered, spectacles 0*5 D
less than the retinoscopy ; continuous occlusion of
R. E. for seven days ; after that, one drop of liquor
atropinae to be put into R. E. only every morning.
December 7, 1897. — Child uses R. E. (atropised) in
distant vision, and L. E. (unatropised) in near vision.
Angle 17 with glasses. Ordered, continue.
February 8, 1898. — Child now uses (unatropised)
L. E. always, both in near and distant vision, and
squints always with (atropised) R. E. Ordered, stop
using the atropine and come again in a month.
June 29, 1899 (one year and four months later). —
Soon after the last visit the child's father, a bank
manager, was transferred to a post in the north of
England. The mother said that, as she was not able
to bring the child to me, she thought she had better
continue the drops. She used the drops, for the R. E.
only, every day for about six months. Not since.
The child has now constant squint R. E. 11°, with the
glasses. Ivory-ball test shows vision of L. E. to be
perfect, but vision of R. E. is barely ^%. Central fixa-
tion is present in R. E. but unsteady.
Of course all possible means have since been used
to restore the sight of the R. E. The child has now
learnt to read. On November 8, 1901, the vision of
7 2
AMBLYOPIA
the L. E. (which at first squinted) was |, and the
vision of the R. E. (which was at first the fixing eye)
was iL.
Case D, 332. On May 9, 1900, I saw, at Moorfields,
a boy, aged 3 years 2 months. He had squinted con-
stantly, R. E., since the age of 2 years 8 months. Xo
heredity. Abversion perfect. C. S. R. E. 46 . Good
central fixation R. E. Easily sees half-inch ivory ball
at about 20 feet with R. E. Ordered, atropine both
eyes for retinoscopy.
May 16, 1900. — C. S. R. E., with atropine, 37 .
Retinoscopy R. E. + 7 I) sph. + 1-25 D cyl. ax. vert.
L. E. + 6*25 D sph, + 1-5 D cyl. ax. vert. Ordered,
glasses o - 5 D less than retinoscopy ; also, guttas atro-
phias 1 per cent. L. E. only every morning. To return
in one month.
June 5, 1901 (thirteen months later). — Mother used
drops for L. E. for a month, but was then ill, so child
has since been neglected. The glasses have been worn
constantly. C. S. R. E. 36 . R. E. has lost the power
of central fixation. Ordered, continuous occlusion
L. E. for one month.
July 3, 1901. — Central fixation, R. E., regained.
Ordered guttas atrophias 1 per cent. L. E. only every
morning for two months.
August 28, 1901. — Patient uses L. E. (atropised) in
distant vision, and R. E. (unatropised) in near vision.
Ordered, continue drops L. E. only, for two months.
December 4, 1901. — Drops have been used until
three weeks ago, not since, as they were all finished.
Child now, without atropine, uses the originally squint-
ing R. E. always, and squints constantly with the
originally fixing L. E.
April 2, [902. — Last time 1 accidentally omitted to
give the mother written directions ; there w.is, there-
fore, some misunderstanding. Child now squints con-
stantly with L. E. (the originally fixing eye) 24 . L. E
CONGENITAL AND ACQUIRED J 3
has central fixation, but very unsteady. Ordered,
guttae atrophias 1 per cent. R. E. only, every morning
for one month.
May 7, 1902. — Child will not use (unatropised) L. E.
voluntarily even in near vision. Ordered, continuous
occlusion R. E. for one month.
June 4, 1902. — Steady central fixation L. E.
Ordered, discontinue pad and use guttae atropinae
R. E. only, for two months.
August 6, 1902. — Child now uses L. E. (unatropised),
and squints with R. E. (atropised), always in near
vision, and usually in distant vision also. Ordered,
stop drops.
August 30, 1902. — Child now uses either eye in-
differently, alternating convergent squint 24 , with
glasses.
Case D, 286. October 9, 1900. — Girl, aged 5 years
7 months. She began to squint suddenly at the age
of 3 years 9 months, and had squinted constantly
ever since. Already under atropine. C. S. L. E., 36 .
Retinoscopy, R. E. + 4-5 D sph. + 0*25 D cyl. ax.
horiz. ; L. E. same at approximate macula. Fixation
lost L. E. Ordered glasses + 4 D sph. each eye.
R. E. to be continuously occluded for one month.
August 9, 1 90 1. — Case has been neglected, except
that glasses have been worn. V. R. E. f, V. L. E. -^.
No fixation L. E. Ordered, continuous occlusion R. E.
for three weeks.
August 30, 1901. — Treatment carried out. Good
central fixation L. E. V. L. E. T %. Ordered, guttaa
atropinae R. E. only, for six weeks.
October 4, 1901.— V. L. E. f. C. S. 16 . Child uses
L. E. (unatropised) in near vision and R. E. (atropised)
in distant vision. Ordered, continue atropine R. E.
only, for two months.
December 3, 1901. — Vision § each eye. Child uses
L. E. and squints with R. E. always, both in near and
74 AMBLYOPIA
distant vision. Ordered, stop atropine and come in
two weeks.
May 6, 1902. — Child has not been seen for live
months. She has squinted constantly with K. E. (the
originally fixing eye) during that time. V. R. E. T *^,
V. L. E. f. Amblyopia to ^ acquired in R. E. since
last December. Ordered, gutt?e atropine L. E. only,
for one month.
June 6, 1902.— Squints now with L. E. (atropised)
1 8°. V. § each eye.
NOTE. — This case is altogether exceptional, on
account of the age (nearly seven years) at which
amblyopia in the R. E. was acquired.
Amblyopia ex anopsia, like congenital ambly-
opia, concerns almost entirely the central and
paracentral region of the retina, and produces no
contraction of the peripheral limits of the field
of vision. But the blindness often reaches an
extreme degree which is never met with in the
congenital form. In congenital amblyopia the
central vision is never lower than ^, the visual
acuity normally found at 5 from the fixation
point. In an extreme case of acquired blind-
ness, on the other hand, there is often a scotoma
extending about 25 to 30 round the centre of
the field of vision. In this scotoma there may
be bare perception of light. Outside this area
fingers may be counted a foot or two from the
face.
Amblyopia in Casks ok Convergent Squint.
Congenital and acquired amblyopia having been
studied separately, one is now in a position to
CONGENITAL AND ACQUIRED 75
discuss the cause of the blindness so often found
in cases of unilateral convergent squint. In any
individual case, seen for the first time when the
squint has lasted several years, it is impossible
to say how much of the blindness may be due to
disuse of the deviating- eye, and how much may
be congenital. Statistics, however, enable one
to draw a very accurate general conclusion.
Tables iii., iv., and v., show the visual acuity
of the deviating eye in cases of constant uni-
lateral convergent squint. I used Snellen's types
or the ivory-ball test at the first visit, when
possible, and on many subsequent occasions.
Nearly all these children have since become old
enough to allow me to confirm the results of
the ivory-ball test by Snellen's types. The
visual acuity noted in the tables is the final
result, with optical correction, and after all
possible means had been used to remove any
acquired amblyopia.
I have included in the tables only cases in
which I could be reasonably certain as to the
time of onset of the deviation, and in which
my directions were subsequently followed to
my satisfaction. The cases had either received
no treatment before I first saw them, or they
had merely been given glasses. Some had
been operated upon.
Any defect of vision found in the cases in
table iii. may be considered as congenital. In
76
AMBLYOPIA
these recent cases, any amblyopia which might
have been acquired would certainly have been
removed by the subsequent treatment.
Table iv. shows the visual acuity of the deviat-
ing" eye after all possible means had been used
to remove any defect which might be present.
The vision was at first, in many cases, very
considerably lower than shown in the tables.
In the cases in table v. the squint had, in
most cases, lasted so long that no improvement
in vision was possible.
A comparison of table iii. with table v. shows
that congenital amblyopia only occurs in a very
small proportion of the cases, and is never re-
sponsible for the extreme blindness so often
found in neglected cases of unilateral squint.
Tables Showing the Visual Acuity of the Deviating
Eye in 787 Cases of Constant Unilateral Con-
vergent Squint.
Table III.
Cases which I saw first when the patient had squinted during
less than one-eighth of his or her life.
Vision of the
deviating eye.
Age ol
lset of the deviation.
Before
12 months.
1 to 3 yrs.
After 3 yrs.
Total.
i
33
62
80
165
f and A
2
6
9
17
T 6 g and q^
1
3
5
9
3 6 8 and B 6 a
1
1
2
Less than g'V
Fixation lost
O
irrecoverably
CONGENITAL AND ACQUIRED
7
Table IV.
Cases which I saw first when the patient had squinted during
more than one-eighth and less than on?-half of his or her life.
Vision of the
deviating eye.
f and T %
^g and 5 6 ¥
B <V and v %
Less than %%
Fixation lost
irrecoverably
Age of onset of the deviation.
Before
. i o •? yrs.
12 months.
After 3 yrs.
Total.
Table V.
Cases which I saw first when the patient had squinted dnrin>
more than one-half of his or her life.
Vision of the
deviating eye.
Age of onset of the deviation.
Before
12 months.
i to 3 yrs.
After 3 >rs.
Total.
'i
f and ^V
T e 8 and &
36 and e 6 o
Less than e 6 s
Fixation lost
irrecoverably
o
2
4
8
55
56
3
7
32
53
103
1 10
11
19
54
4i
2 5
14
28
90
102
179
191
When I have been consulted about a case of squint, I
have always warned the parents of the patient that, in the
event of a younger member of the family developing a
squint, the case ought to receive attention without delay.
I have, therefore, been fortunate enough to see an unusually
large proportion of my cases soon after the first appearance
of the deviation.
It is remarkable that only eight cases, commencing
before twelve months of age, appear in table iv. This is
evidently because parents who have been warned, and
those who are especially solicitous for the welfare of their
children, seek advice immediately. These cases are included
in table iii. The other infants are usually left without
treatment for several months, so that they appear in table v.
7§
CHAPTER VI.
THE METHOD OF INVESTIGATING A CASE OF
SQUINT.
Every case of squint should be systematically
investigated, as it is only by a thorough knowledge
of each case that a rational line of treatment can
be determined upon. The following is the plan
I always use. It may appear rather formidable
at first sight, but, with practice, one can carry out
the various tests with great rapidity and precision.
The time will surely not be grudged when it is
remembered that, in cases which are presented
early enough, the patient's whole future career
may depend upon the skill and care of the surgeon
who first sees the case.
(i) History.
(2) The character of the squint
(3) The power of fixation in the deviating eye.
(4) Movements of each eye separately. Dyna-
mic convergence.
(5) Vision testing.
(6) The condition of the fusion faculty.
(7) The angle of the deviation.
INVESTIGATION OF SQUINT 79
After using atropine for from three to eight
days : —
(8) The refraction.
(1) History. — Under this head should be
noted : (a) Age of onset, when it can be deter-
mined. It may often be fixed very precisely by
reference to some family event, such as the birth
of the next child, (b) Mode of onset. Whether
it began as an occasional squint or was constant
from the first, (c) Any illness or injury imme-
diately preceding the appearance of the deviation
e.g., whooping cough, measles, a blow on the
head, "fits," severe fright, &c. (d) Evidence
of heredity — squint in brother, sister, or parents
of the patient.
(2) The Character of the Squint. — The
presence of a deviation and its character, whether
convergent or divergent, unilateral or alternat-
ing, may often be determined by simple inspec-
tion. But appearances are sometimes misleading,
e.g., the high angle gamma often found in hyper-
metropes may simulate a divergent squint or
mask a slight convergent squint. The low, or
even negative, angle gamma usually associated
with myopia may give an appearance of abnormal
convergence or mask a slight divergence.
The cover test is at best only a rough test having
many sources of error. It is, moreover, not possible
to use it with young children. Hut, as it is very
generally employed, it will be well to describe the
8o INVESTIGATION OF SQUINT
proper method of making the test, and the fallacies to
be guarded against.
Tell the patient to look steadily at some distant
object. Take a narrow card or folded paper and, with
a rapid lateral movement, cover, say, the patient's left
eye, taking care not to touch his face. If the right
eye makes no movement it was probably 1 not squinting.
Now uncover the left eye, and see that the patient
looks steadily at the distant object. Screen the
patient's right eye in the same way. If the left eye
makes no movement it was probably 1 not squinting
either. If, however, when one eye is covered, the
other has to make an outward movement in order to
fix the object, it was previously squinting inwards ; if
it rotates inwards it was squinting outwards.
In a case in which the patient has been shown to
have a squint, but in which he can fix with either eye
at pleasure without the other eye being screened, and
can maintain fixation after a momentary closure of the
lids, the squint is alternating.
In some occasional squints and heterophorias, while
both eyes fix truly when uncovered, either eye deviates
when screened, but immediately recovers itself on
removal of the screen.
The mirror lest. — This is an entirely satisfac-
tory test, and can be used quite well even in the
case of the youngest infants. The patient should
be in the dark room, with the lamp behind him.
The light is reflected from the mirror of an
ophthalmoscope, from a distance of about 2 ft., into
the patient's eyes. An infant will immediately
look at the mirror ; an older patient should be
1 If the eye has lost the power of central fixation, it may
perhaps make no movement, or it may move in a direction
which would mislead any but a careful observer.
INVESTIGATION OF SOUINT 8 I
told to do so. A tiny image of the ophthal-
moscope mirror is formed on the patient's cornea.
Owing- to the angle gamma, this reflection of the
mirror is usually slightly to the nasal side of the
centre of the pupil. By flashing the light rapidly
from one eye to the other, any want of symmetry
in the position of the reflections is at once
detected. It may easily be seen, too, which is
the deviating eye, and, with practice, a very good
guess as to the extent of the deviation may be
made. 1
Squint or paralysis. — In the case of a patient
who is old enough to speak, the persistent diplopia
would prevent one mistaking' a case of paralysis
of one or more of the external ocular muscles
for a case of comitant squint.
But, in the case of an infant who has recently
suffered from diphtheria, an objective test is
required. The patient is on the nurse's knee in
the dark room, with the light behind him. The
nurse holds his head immovable. The light is
thrown into his eyes, from an ophthalmoscope
mirror, from a position slightly to one side of
him. When he fixes the mirror the approximate
1 According to Hirschberg, when the reflection on the
squinting eye is at the margin of the cornea the angle of
the deviation is about 45 , when it is at the margin of an
average-sized pupil the angle is about 15 . Allowance
should be made for the estimated size of the angle
gamma.
82 INVESTIGATION OF SQUINT
degree of his deviation is noted. The light is
next thrown into his eyes from the other side.
If, when he again fixes the mirror, the angle of
the deviation is greater or less, we have to deal
with a paralysis or paresis, and not with a
comitant squint.
In carrying out the test, it is essential that the
light be thrown into the eyes in both cases from
approximately the same level, as, in many cases
of true squint, the eyes converge more on looking
down and diverge more on looking up.
(3) The Power of Central Fixation. — An
exceedingly important point, in its bearing on the
treatment and prognosis of a case of unilateral
squint, is the presence or absence of the power
of central fixation in the deviating eye.
The patient being in the dark room, with the
light behind him, throw the light from an ophthal-
moscope mirror first into his good eye, while he
looks at the mirror. Note the position of the
reflection of the mirror on the cornea of this eye.
Then cover the good eye, and note whether the
previously deviating eye can now fix the mirror
so as to bring the corneal reflection into a corre-
sponding position. If it does so, there is central
fixation. There may be no fixation, in which
case the eye wanders. Or there may be false
fixation, in which case an eccentric part of the
retina is used for the purpose. An eye which at
first appears to have lost fixation may some-
INVESTIGATION OF SQUINT S3
times, with a little patience, be induced to fix
correctly.
In the clinics one frequently sees some such proce-
dure as the following : The surgeon covers the patient's
good eye, then asks him to follow the movement of his
ringer with the deviating eye. If he is able to do so,
it is assumed that he has central fixation in this eye.
This is entirely fallacious. If the deviating eye has
any sight at all it can usually follow the movements
of a large object. If the deviating eye has false
fixation in a position of only slight convergence, even
the most prolonged examination by this method will
certainly lead to error.
(4) The Movements of each Eye Separately
should be tested by covering- one eye and getting
the patient to look with the uncovered eye from
side to side and up and down. The test is then
repeated with the other eye. This may usually
be done even in the case of young infants by
showing them something in which they are likely
to take an interest. If each eye can be separately
abverted until the edge of the cornea touches the
outer canthus, abversion may be considered full.
The power of adversion varies considerably within
normal limits, Most people can advert each eye
separately until the corneal margin is within less
than one-tenth of an inch of the caruncle.
Dynamic Convergence. — A careful distinction
should be made between static and dynamic con-
vero-ence, iust as static and dynamic refraction are
distinguished from each other.
84 INVESTIGATION OF SQUINT
When a person looks at a distant object, if he
has no squint the static convergence of the eyes
is nil. If he has a convergent squint there is a
static convergence corresponding to the angle of
the squint. If he has a divergent squint, the
static convergence is a negative quantity.
If now he fixes a near object, there is superadded
to the static convergence a dynamic convergence.
A person who in distant vision has no squint,
will usually exercise just sufficient dynamic con-
vergence in near vision (in association with dynamic
refraction, or accommodation) to allow him to fix
the object correctly with both eyes. If, however,
his dynamic convergence be excessive, the eyes
will tend to squint inwards in near vision. A
perfect fusion-sense will keep this tendency in
check. But if the fusion-sense be defective, this
tendency will be free to cause a squint in near
vision. In a case of divergent squint, when the
fixing eye accommodates for a near object the
divergent eye will usually recover itself to a
certain extent. In convergent squint, the faulty
eye should turn in still more towards the nose
in near vision. As will be seen later, the esti-
mation of the dynamic convergence is of the
utmost importance in deciding the; question of
operation for squint. /
Method of climating the dynamic convergence
in a case of squint. -Stand at arm's length
from the patient. Shut one eye and hold the
INVESTIGATION OF SQUINT 85
point of the finger, or perhaps some more
attractive object, in line with the open eye and
the patient's fixing eye. Let the patient look at
the object while it is gradually brought nearer
his fixing eye. The fixing eye will remain
immobile, the deviating eye manifesting the con-
vergence of both. In this way, the slightest
movement of convergence of the deviating eye
can at once be seen, and the point at which the
deviating eye begins to diverge again can be
accurately noted. This simple procedure should
never be omitted.
(5) Vision Testing. — (a) The vision of patients
who are old enough to read letters should be
tested with Snellen's distant types. This would
appear a very simple matter, yet it is surprising-
how often, in the clinics, one finds the vision of
the better eye recorded as the vision of each eye,
even by experienced assistants. The desire to
use the accustomed eye is so strong that, when
this is shaded, the patient will involuntarily screw
his head round to try to see past the shade.
{b) Ivory-ball test for young- children. — Apart
from its scientific interest, it is often of great
practical importance to be able to estimate approxi-
mately a young child's visual acuity. For this
purpose I use five little ivory balls varying in size
from half an inch to one and a half inches in
diameter. The child is first allowed to handle the
balls with both eyes open. Then one eye is covered
7
86 INVESTIGATION OF SQUINT
by a pad, or, if, he wears glasses, by a piece of cotton
wool stuffed behind the lens. He is then asked
to go and pick up the balls as they are thrown on
the floor to a distance of six or seven yards, one
by one, beginning with the largest. By spinning
the ball in the fingers as it is thrown, it can be
made to "break" on touching the floor, so that it
does not go quite in the direction in which it
appeared to have been thrown. It is easy to tell,
by the way in which the child runs for the ball,
whether he really sees it before he starts or is only
going to look for it. I test the presumably better
eye first, so as to give the other eye the benefit of
experience.
Children are always ready to play this ball
game. This method of vision-testing only takes
a few minutes, and it succeeds with most children
who are old enough to walk. I have used it since
1896, and, in cases in which I have subsequently
been able to test the vision by means of Snellen's
types, I have found my conclusions confirmed.
(6) The Condition of the Fusion Faculty
may, as a matter of convenience, be investigated
at this point, but it is usually better to defer the
examination until the state of the refraction has
been ascertained and the effect of the mydriatic
has passed off.
Examination with the amblyoscope I have found
by far the most rapid, precise, and reliable method
of ascertaining the condition of the fusion sense.
INVESTIGATION OF SQUINT 87
Of late years I have used it to the exclusion
of all other methods. It is fully described in
chapter viii.
I wish again to draw attention to the distinc-
tion between the possession of the fusion faculty
and the presence of binocular vision. A patient
may have a convergent squint of very high
degree, with suppression of the vision of the
deviating eye, and yet training with the amblyo-
scope may have perfectly developed his fusion
faculty. In this case, if the patient looks into
the amblyoscope while the instrument is adapted
to the angle of the squint, he fuses the pictures
— his fusion faculty finds its expression in the act
of binocular vision. The same thing happens
when his eyes are put approximately "straight"
by operative or other means.
Javal, Maddox, and others estimate the " depth of
suppression " by the ease or difficulty with which
diplopia may be artificially elicited. Diplopia may
sometimes be elicited by placing a red glass before
the better eye and alternately covering and uncover-
ing it while the patient looks at a candle flame. There
is a fallacy here which must be guarded against — the
patient recognises the fact that he sees a red light
with the "good" eye, and that, when this is covered,
he sees a white light. He therefore often says he sees
two lights, a red and a white, even though he does not
see them both simultaneously. If the red glass fails
to produce diplopia, success may often be attained by
placing a horizontal prism before the deviating eye, so
as to throw the image of the flame on a part of the
retina nearer the macula.
88 INVESTIGATION OF SQUINT
Some writers have recommended, as a test, placing
a prism vertically before one eye, to throw the false
image out of what they call the " band of suppression."
Diplopia can almost always be elicited in this way,
even in cases of total absence of the fusion sense.
The explanation of this is not far to seek. The con-
jugation of the two eyes in horizontal movements,
being intended to subserve the act of binocular vision,
was probably acquired at no very early period in the
development of the human race. The conjugation of
the eyes in vertical movements, on the other hand, I
believe we share to a great extent with most of the
mammals. It is not surprising that disturbance of
this very ancient function, by vertical displacement
of the image in one eye, should produce diplopia.
But diplopia tests really give very little information
as to the condition of the fusion sense. Some cases,
in which diplopia is with difficulty elicited by these
methods, readily get the highest grade of binocular
vision after fusion training with the amblyoscope, and
are subsequently completely cured. Others, again,
who easily see double, may be incapable of acquiring
more than grade i binocular vision.
7) The Measurement of the Angle of
the Deviation. — At the first, and at each sub-
sequent visit, the angle of the deviation is
accurately measured. When the child has been
ordered glasses, the measurement is always made
with the glasses on. The case-sheet then shows
at a glance the progressive effect of the treat-
ment upon the deviation, and helps one to decide
whether it is advisable to supplement this treat-
ment by operation.
Four methods of measuring the angle of devia-
tion are here described.
INVESTIGATION OF SQUINT 89
(a) The deviometer} — This instrument can be
very rapidly used, no adjustment being required.
Measurements obtained by it are very accurate.
It can be used quite easily even with the youngest
children.
A wooden stand, about 10 inches high, supports
a horizontal wooden arm, 2 inches wide, \ inch
thick, and about 2 feet long. This arm is
pivoted at the end, so that it may be swung
over to either side as required. The arm is
painted black in front. On the back is a
scale of tangents to degrees at 60 centimetres
distance. A flat, hook-shaped piece of brass,
having a white spot on it, slides along the arm.
In front of the pillar, below the zero of the scale,
is a specially made electric lamp, 5 inches high
and f inch in diameter. Flexible wires go from
the electric lamp to the wall plug. An electric
bell-push is used instead of a switch, so that, by
pressing the button, the light may be flashed on
and off very rapidly. A string 60 centimetres
long is attached to the upright pillar of the instru-
ment. At the end of the string is a ring.
Measurements and details of construction of
the deviometer will be found in the appendix.
The instrument is put on a table. The nurse
1 I have no wish to claim originality for this instrument.
The principle is that of Maddox' scale and Priestley
Smith's tape, the former of which I used for years before
I devised the deviometer.
go
INVESTIGATION OF SQUINT
sits at the table with the child on her knees. She
puts the ring on her finger, and holds the child's
head steady with her hands, keeping the string
taut. The surgeon "sights" the child's eyes
through the nick in the top of the stand, and
Fig. 9.
presses the button. The child immediately looks
at the light with his fixing eye. The reflection
of the lamp forms a vertical line of light on the
cornea of this eye, which shows the correct
position of fixation. The position of the line of
light on the cornea of the squinting eye enables
a good guess to be made as to the angle of the
deviation. The light is discontinued. The brass
INVESTIGATION OF SQUINT 9 1
traveller with the white disc is slid along the arm
to the position which corresponds to the guess.
The brass traveller being tapped with the finger,
the metallic sound causes the child to look at it.
If it does not, a lighted match, held in front of
the traveller, will always attract his attention.
The button is then pressed, and the light flashed
on for an instant. If the line of light on the
cornea of the squinting eye is in a corresponding
position to that which it formerly occupied in the
fixing eye, the angle of the squint is read off on
the scale on the back of the arm. If not, the
traveller is moved a little, and when the child
looks at it the light is flashed on again, and so
on till the true position is found.
An older patient can, of course, sit at the table
and hold the string himself, and look at the zero
of the scale, or the white disc on the traveller,
when directed to do so.
(b) Maddox tangent scale (fig. 20, page 171) is
an admirable device for measuring the deviation.
The method is very rapid and accurate. It is
not, however, easy to use with small children. I
always use it at Moorfields, because the apparatus
is fixed in the wall out of harm's way, and there
is nothing to get out of order, however roughly it
may be used.
The large figures are used for measuring
heterophorias with the Maddox rod. With these
we are not at present concerned. The small
Q2 INVESTIGATION OF SQUINT
figures, in the horizontal scale, represent tangents
to degrees at a distance of one metre. They are
printed on a strip of paper, which is pasted on
a board about seven feet long. In the centre
of this scale is a candle. Below the candle is
attached a light bamboo rod one metre long.
The patient rests his cheek against the end of
the metre rod. The surgeon puts his head below
the rod, so that his eye is vertically below the
rays of light which pass from the candle to the
patient's face. The patient is first told to look
at the light. The position of the image of the
candle flame on the cornea of the fixing eye is
noted. A guess is made as to the angle of the
squint. The patient now is told to look at the
figure which represents the guess. If this is too
much or too little, other figures are named till
the reflection of the candle flame on the cornea
of the deviating eye occupies a position similar
to that which it formerly occupied in the fixing
eye.
(c) Priestley SmitJi s tape method. — The advan-
tages of this method are that it takes very little
time and the apparatus required is simple. It is
moderately accurate. It is, however, not easy to
use with young children.
A string one metre long has a ring at one end.
To the ring is attached a graduated tape. The
tape has a weight at its other end. The patient
holds the free end of the string against his temple.
INVESTIGATION OF SQUINT 93
The surgeon puts the ring on a finger of one of
his hands in which he holds an ophthalmoscope
mirror. The tape is allowed to slide between the
fingers of the other hand, the weight keeping the
tape taut. The patient is first told to fix the
mirror, while the light of a lamp is reflected into
the fixing eye. The position of the image of the
mirror, on the cornea of the fixing eye, is noted.
The light from the mirror is now thrown on to
the deviating eye, and the patient is directed to
look at the surgeon's tape hand. This is moved
horizontally, till the position of the image of the
mirror, on the cornea of the squinting eye, is
similar to that which it formerly occupied on the
cornea of the fixing eye. The string keeps the
ophthalmoscope hand at one metre from the
patient's eye. The observer keeps the tape hand
as nearly as possible at the same distance from
the patient's eye. The graduated scale on the
tape, where it slides through the tape hand, shows
approximately the angle of the deviation in degrees.
If the length of the string be made 60 cm. instead
of one metre, an ordinary Continental tape measure
may be used for the graduated tape, one centimetre
representing approximately one degree.
(d) The perimeter method. — I describe this
because a perimeter is to be found in every eye
clinic and ophthalmic surgeon's consulting room.
The patient is seated at the perimeter, which is
adjusted so as to bring his deviating eye accurately
94 INVESTIGATION OF SQUINT
in centre of the arc. A candle is placed at the far
end of the room, in line with the zero of the peri-
meter and the patient's deviating eye. He is told
to look steadily at this candle with his fixing eye.
A second candle or taper, with the eye of the
surgeon looking exactly over the top of the flame,
is carried round the arc of the perimeter till the
reflection of the flame lies in the centre of the
cornea of the deviating eye. The position of the
taper on the graduated arc of the perimeter,
shows the angle of the squint in degrees.
This is a wretched method. It is inaccurate,
as it takes no account of the angle gamma. It
cannot be used in the case of a small deviation,
as the surgeon's head then prevents the fixing eye
seeing" the distant candle. It cannot be used for
young children. The preliminary arrangement
takes up so much time that a surgeon who relies
upon this method is apt to neglect to measure the
squint at all.
The angle gamma may be measured separately, if
the patient's squinting eye has not lost the power of
central fixation. Cover the fixing eye. Let the
patient steadily C\x the zero of the perimeter with the
squinting eye. The taper with the surgeon's eye
looking exactly over it, is carried along the arc till the
reflection of the flame appears in the centre of the
cornea. The position of the taper on the graduated
arc shows the size of the angle gamma. This angle
gamma should be added to the perimeter measurement
of a convergent squint and subtracted from that of a
divergent squint.
INVESTIGATION OF SQUINT 95
(8) The Refraction. — This is examined by
retinoscopy, after atropine has been used, for both
eyes, three times a day, for from three to eight
days. For young children I prefer the atropine
ointment, i per cent. Atropine drops, if used too
freely, occasionally cause unpleasant symptoms,
whereas the ointment almost never causes trouble.
The nurse or mother should be shown how to
insert the ointment within the lower eyelid with a
glass rod. One now and then sees a young child
in whom atropine produces perfect cycloplegia
with only very slight mydriasis.
Children of two years and upwards may, with a
little tact, usually be induced to allow one to put
on a trial frame and proceed with retinoscopy in
the usual way.
In the case of a very young child, a different
plan must be followed. The nurse sits in the
dark room with the child in her arms. The light
is placed above and behind the child's head. The
light being reflected from the ophthalmoscope
mirror into the child's fixing eye, he immediately
looks at the mirror. The lenses are handed, one
by one, to the nurse, who holds them up before
the fixing eye, or the surgeon may hold the lenses
himself. There is seldom much difficulty so far.
Now, in order to investigate the deviating eye, it
is necessary to screen the fixing eye. The child
may, perhaps, not tolerate any screen held near
his face. In this case, I hold a black cardboard
Q6 INVESTIGATION OF SQUINT
screen, about halfway between the child's face and
my own, in such a way as to cut off the view of
the mirror from the child's fixing eye. The light
now being thrown into the deviating eye, the
child looks at the mirror with this eye. If
central fixation in the deviating eye of one of
these very young children has already been lost,
one can only make an approximate guess as to
the refractive error of this eye. A glass may
then be ordered provisionally, to be exchanged
for an accurate correction when one has succeeded
in restoring central fixation.
In the case of an older patient, one can measure
very accurately the refractive error of an eye which
has lost fixation. Throw the light into the fixing
eye, and note the position of the reflection of the
mirror on the cornea, while the patient fixes the
mirror. Now direct the patient to look at a small
white card, which is held three or four feet away
from him by an assistant. Throw the light on to
the cornea of the deviating eye, and manoeuvre
the card till the reflection of the image on the
cornea is in a position corresponding to that
which it formerly occupied in the fixing eye. Now
proceed with the retinoscopy.
CHAPTER VII.
THE TREATMENT OF CONVERGENT SQUINT.
I propose to describe first the treatment I
adopt in cases of constant unilateral squint.
Any modification of treatment required in occa-
sional or alternating cases will be considered
afterwards.
The objects to be kept constantly in view in
the treatment of squint are — (a) To prevent
deterioration of the vision of the deviating eye,
and to restore, as far as possible, the sight of this
eye in cases in which amblyopia from disuse has
already been allowed to occur. (6) To endeavour
to remove the fundamental cause of the squint,
by training the fusion sense at the earliest pos-
sible age. (c) To restore the visual axes to their
normal relative directions.
There are five therapeutic measures at our
disposal, any or all of which it may be necessary
to use in our endeavour to attain these objects,
(i) Optical correction of any refractive error
which may be present. (2) Occlusion of the
fixing eye. (3) Instillation of atropine into the
fixing eye only. (4) Training the fusion sense.
(5) Operation.
98 THE TREATMENT OF
( i ) Optical Correction. —As has been demon-
strated in chapter iv., the essential factor which
allows a deviation to occur is a defect of the
fusion faculty. The eyes then, being uncon-
trolled by the necessity for fusion, are for a time
kept approximately " straight " by their motor
coordinations. But they are in a state of unstable
equilibrium, and are ready to squint, either in-
wards or outwards, in response to influences which
would have no effect if the fusion faculty were
normal. In a very large proportion of the cases
it is the state of the refraction which chiefly
determines whether the eyes shall deviate in-
wards or outwards. Thus, in the great majority
of cases, the eyes of hypermetropic squinters
deviate inwards, and the eyes of myopic squinters
deviate outwards. It is rational treatment, there-
fore, to attempt to overcome the deviation by
optical correction of any refractive error which
may be present.
In cases of simple hypermetropia, or hyper-
metropic astigmatism, or compound hyperme-
tropic astigmatism, my usual practice is to order
spectacles fully correcting any astigmatism which
may be present, and correcting all but o"5 d of
the hypermetropia. The reason for the slight
under-correction of the hypermetropia is this : —
When the effect of the atropine, used for the
retinoscopy, has passed off, some of the hyper-
metropia will in any case become "latent," so that
CONVERGENT SQUINT 99
fully-correcting glasses, which gave perfect distant
vision under atropine, will, when its effect has
passed off, make all distant objects appear misty.
This blurring of distant objects not only shortens
the child's range of vision at a time when the
acuity of the physical senses has the most marked
effect upon his mental development, but the
effort to see distinctly actually appears to affect
unfavourably the angle of the deviation. 1
In a case of mixed astigmatism, the refractive
error should be exactly corrected.
A certain percentage of cases of convergent
squint are myopic. Any myopic astigmatism
should of course be exactly corrected. But as
regards simple myopia, it might naturally be
thought that a considerable under-correction
would tend to lessen the abnormal convergence
by preventing any effort of accommodation even
in near vision. I began by acting upon this
assumption, but was gradually forced by experi-
ence to abandon it. I find that the best results
are obtained by exactly correcting any myopia
and myopic astigmatism which may be present.
Myopes who begin early to wear fully-correcting-
1 I have taken over a considerable number of hospital
squint cases which were formerly under the care of a
colleague, who used habitually to over-correct the hyper-
metropia to the extent of 1 D. In the majority of these
cases the deviation became less within a few weeks of
ordering glasses with which the patients could see dis-
tinctly.
lOO THE TREATMENT OF
glasses, use them quite comfortably for all purposes,
and appear to have as good a range of accommo-
dation as emmetropes.
In a case of anisometropia, the refractive error
of each eye should be corrected according to the
preceding rules. This applies even to cases in
which one eye is hypermetropic and the other
myopic.
When glasses are ordered, it is a good plan,
especially with young children, to continue the
atropine, which has been used for the retinoscopy,
until the glasses arrive from the optician. It
should then be discontinued. Even an infant
soon discovers that he sees better with the glasses
than without them, and by the time the effect of
the atropine has passed off, the wearing of glasses
has become as much a habit as the wearing- of
clothes.
The glasses should be worn constantly, except
when the child is in bed at night. They should
never be removed at any other time, except for
toilet purposes.
In the case of children who are old enough to
attend school, some surgeons order one pair of
glasses for distant vision and a stronger pair for
reading. I have tried this plan and found it most
unsatisfactory. In changing from one pair to
the other there is often a considerable interval in
which no glasses are worn at all. Besides, the
exercise of a noi'mal amount of accommodation in
CONVERGENT SQUINT IOI
association with dynamic convergence, in near
vision, is a physiological act, and its suspension
has not appeared to me to have permanently
lessened the angle of the squint.
The quality and fit of the spectacle-frames are
very important. Steel is the best material for
children. Steel frames of good quality will
remain without rust for a long time, if the child
be kept moderately clean. After a time, the
growth of the child's face will necessitate larger
frames. For infants and young children the
lenses should be circular, 1 or oval with their long-
axes vertical, in order that there shall be no
temptation for the child to look over them. The
lenses should be as large as possible, and should
be centred for distant vision. They should be as
close to the eyes as they can be without touching
the lashes. The bridge piece, which arches over
the bridge of the nose, should be of tempered
steel, broad, flat, and strong, and should be very
accurately fitted. A broad thin plate of tortoise-
shell, carefully fitted under the arch of the bridge
piece, prevents rust and distributes the pressure
over a larger area. Spectacles for children of
1 Circular lenses, however, have this disadvantage —
unless the spectacles are carefully made, the lenses are apt
to rotate in the frames, so that the axes of cylinders become
displaced. This may be prevented by putting a little
Canada balsam in the groove of the rim. If it should be
necessary, at any time, to replace a cracked lens, the
balsam may be melted by a moderate heat.
8
102
THE TREATMENT OE
3 years and upwards should have flexible curl
sides to hook behind the ears.
Infants and very young children should have
their o-lasses tied on. The sides, in this case,
should be straight and should have a loop at the
end. They should be very short, only reaching
to just above the ear. About f inch near the loop
should be wrapped with wool. The glasses are
tied on by tapes, passed through the loops, behind
the child's head. These frames are very com-
fortable. If the sides were of the usual length
the tapes would act at the end of a long lever,
causing pressure above the ear, and perhaps
ulceration of the tender skin of the infant.
When the infant is put down to sleep in the
daytime these frames are not removed. These
CONVERGENT SQUINT 103
very short sided do not press on the pillow and lift
the glasses from the child's face.
It is usually stated that children under three or
four years of age are too young for glasses. No
infant is too young to wear glasses should they
be required. Many of my squinting patients have
begun to wear spectacles such as I have described,
long before twelve months of age.
Of course young children sometimes break their
glasses, but I have never known a case in which
the eye has been injured thereby. The lens,
being held in the frame, does not break into
splinters but cracks across, or chips at the edge.
(2) Occlusion of the Fixing Eye. — In the
case of a child who has squinted constantly with
one eye for a considerable proportion of his life,
and who has either received no treatment at all or
who has been merely given a pair of glasses, one
usually finds that the deviating eye has become
more or less blind. If the ivory-ball test shows
the visual acuity of this eye to be not less than f s ,
the case may be treated at once in the manner
described in paragraph 3. Often, however, one
finds that the blindness has progressed far beyond
this point, so that the power of central fixation
may have been lost and the visual acuity reduced
to the ability to count fingers close to the face, or,
in some cases, even to bare perception of light.
In a young child, an attempt should always be
made to restore, as for as possible, the sight of
04
THE TREATMENT OF
the deviating eye, by forcing the child to try to
use it. For this purpose I order the fixing eye to
be continuously occluded for a time. It is not a
good plan to order the eye to be occluded for part
of each day only; apart from the fact that this is
not nearly so rapid and effective as continuous
occlusion, the child usually cries every time the
shade is applied, so that the treatment is seldom
properly carried out. When the better eye is
continuously covered, the child soon becomes
accustomed to the shade, so that, after a day or
two, he usually ceases to object to it.
There are several methods of occluding an eye.
each of which may be useful in certain cases.
For infants, a gauze pad secured by a few turns of
bandage answers well. In the case of children
who are beginning to get about, the gauze pad
should be held in place by strips of strapping-
plaster. Children who are well cared for may
have the pad changed every morning. Hospital
patients, however, often leave the pad undis-
turbed for three or four weeks without any harm
resulting.
If the child has a reliable nurse in constant
attendance it may be sufficient to pack cotton
wool behind the spectacle lens. The cotton wool
pad must be carefully applied and the child will
require constant supervision, or he will push the
pad upwards and outwards and peep down the
side of his nose. The gauze pad and strapping is
CONVERGENT SQUINT 1C>5
the only possible method for hospital patients,
whose parents are seldom able to give them much
attention.
I examine the child again at the end of two or
three weeks. If the vision of the deviating eye
be improved sufficiently, the shade is discontinued
and the case treated as described in paragraph 3.
If not, the fixing eye is occluded for another
month, after which the child is again examined.
If occlusion of the fixing eye is going to do much
good, one usually finds a very great improvement
in the vision of the squinting eye within a fort-
night. If this improvement has not taken place
at the end of two months it is seldom worth while
to continue the shade.
(3) Instillation of Atropine into the Fixing
Eye Only. — Atropine has the property of tem-
porarily paralysing the ciliary muscle, and so
suspending the power of accommodation of the
eye. When, therefore, atropine is instilled into a
normal emmetropic eye, or an eye whose refrac-
tive error is corrected by glasses, this eye still
sees distant objects clearly, but is unable to focus
near objects. An unatropised eye whose vision
is only one-sixth or even one-tenth of the normal,
is able to see objects, at the reading distance,
more clearly than a normal eye whose accom-
modation is paralysed by atropine.
In the case of a young patient, the visuai
acuity of whose squinting eye has been shown by
106 THE TREATMENT OF
the ivory-ball test to be not much less than g %, I
order atropine to be put into the fixing eye only
every morning. The child, of course, wears his
glasses at the same time. He will be unable to
see distinctly his toys and picture-books with the
atropised fixing eye. But he quickly discovers
that, by making a conjugate lateral movement of
both eyes until he has brought the squinting eye
to bear on these near objects, he can see them
much more clearly. He acquires the habit of
always using the (atropised) better eye for dis-
tant vision and his (unatropised) worse eye for
near vision. In this way the worse eye is most
efficiently exercised, and amblyopia ex anopsia
prevented. And, in a case in which a consider-
able degree of blindness has already been acquired,
one finds at each visit, if the child be young
enough, a steady improvement in vision. In
many cases, after a few weeks or months of this
treatment, the vision of this previously amblyopic
eye becomes perfect, or nearly so. When the
visual acuity of the (unatropised) "deviating
eye " approaches the normal the child uses this
eye always both in near and distant vision, and
turns in the (atropised) "fixing eye" instead.
I then stop the atropine for two or three weeks to
see what will happen. Usually the child returns
to his old habit of squinting with the eye with
which he squinted at first, and fixing with the
" fixing eye." In this case 1 order atropine every
CONVERGENT SQUINT \Oj
morning for the fixing eye only for the first seven
days in each month. It occasionally happens, in
the case of a young child, that, on discontinuing
the atropine, what was originally the fixing eye
continues to exhibit the deviation. The case
may be left for three or four weeks, but care
must be taken lest this originally fixing eye
now become amblyopic (see Case B, 83, and
Case D, 332, chapter v.). The balance may
easily be kept by, if necessary, atropising the
other eye for a few days.
The use of atropine for the fixing eye only is
an exceedingly efficient curative measure. A
young child spends at least half his waking hours
in looking at near objects. So that when he
uses the (atropised) " fixing eye " in distant vision
and the (unatropised) "squinting eye" in near
vision, this is equivalent to perfect occlusion ot
the " fixing eye " for at least half of each day.
And when his glasses are taken off for any
purpose, if he has much refractive error, he turns
in the atropised " fixing eye " and uses the
unatropised worse eye, even in distant vision.
As regards the form in which the atropine is
used, I usually order one drop of a 1 per cent,
solution of atropine sulphate to be put into the
fixing eye only, every morning. It may be
inserted with a "dropper" or, better still, with
a small camel hair brush or feather. Atropine
ointment answers the same purpose. The lower
108 THE TREATMENT OF
lid should be drawn down, and a small piece
inserted into the conjunctival sac with a glass
rod. Lamellae containing ^oo to T ^ of a grain
of atropine sulphate may be used instead, but
nurses usually find them rather difficult to insert.
I always see the child again within a month of
beginning this treatment, and after that at intervals
of one or two months, according to the nature of
the case. In order that there may be no mistake,
the mother is given a card on which are written
the directions and the date of the next visit. The
treatment is continued until the visual acuity of
the squinting eye becomes equal to that of the
fixing eye, or until no further improvement can be
got. Having employed this method for main-
years, and in a very large number of cases, I am
able to state positively that there is no danger of
its causing any permanent impairment of the
power of accommodation.
This treatment will always prevent the deviating
eye from # becoming amblyopic. Its efficiency in
curing amblyopia which has already been acquired
will be greater the younger the child and the
more recent the deviation. After about seven
years of age usually not much improvement in
vision can be obtained, though I have met with
many exceptions to this rule.
Of course, carefully keeping the fixing eye tied
up for not less than half of the child's waking-
hours would answer as well, if it could be really
CONVERGENT SQUINT IO9
clone. But, whatever the mother and nurse may
promise at first, they will, after a few weeks, find
the amount of supervision required too great a
tax on their time and patience. But even the
hard-worked mother of a large family, attending
a hospital out-patient clinic, finds it no trouble to
put a drop of atropine into the fixing" eye only
every morning, for as long as it may be required.
A disastrous practice, adopted by many surgeons
and invariably recommended in books, is that of
ordering atropine for both eyes for children who are
supposed to be too young for glasses. The object,
of course, is to lessen the convergence by para-
lysing the accommodation. Atropine, used in this
way, never brings about a permanent cure of the
squint, though it occasionally causes a temporary
suspension of the deviation. But the deviating
eye is usually the more ametropic, so that to
paralyse its accommodation with atropine is the
very way to ensure that this eye shall never under
any circumstances be used. The most hopeless
cases one sees, of blindness of the squinting eye,
are those which have been treated with atropine
for both eyes for a few months.
(4) Training the Fusion Sense. — In a case
of unilateral or accidentally alternating squint,
if the child is brought early enough, I endeavour
to remove the fundamental cause of the squint by
training the fusion sense. For this purpose I use
an instrument which I have called " amblvo-
1 IO THE TREATMENT OF
scope." A description of the amblyoscope and
of the method of training" the fusion faculty will
be found in the next chapter. The favourable
time for fusion training is between the ages of
three and five years. In children under three
years of age this treatment is apt to be rather
difficult, though I have succeeded in many cases.
After five years of age the fusion training takes
longer, and a much less powerful "desire for
binocular vision" is obtained. After six years of
age it is seldom worth while to attempt fusion
training at all. It is true that, occasionally, a
patient who has squinted for many years may
have a sort of binocular vision when his deviation
is corrected by operation at a much later date.
But this small degree of fusion sense is not a
fresh acquisition. He had it before he squinted,
but it was too feeble to prevent the occurrence
of a deviation, or even to cause diplopia.
Normally the iusion faculty begins to develop
at a very early age, and, I think, reaches its full
development by about the end of the sixth year.
The education of the fusion faculty, at a time
when this should normally be developing, is very
rapid, easy, and charming in its results. " Stereo-
scopic exercises," undertaken at a time when the
child is old enough to take an intelligent interest
in the process, are infinitely tedious and dis-
appointing.
Of course, one should never omit fusion train-
CONVERGENT SQUINT I I 1
ing in any suitable case which presents itself in
private practice. But in a large hospital clinic, it
is physically impossible to find time for it except
in a few selected cases.
(5) Operation. — In cases of convergent squint
in which the deviation is not overcome by other
means, operation becomes necessary. Two op-
erative procedures are employed either separately
or in combination. They are tenotomy of the
internal rectus muscle and advancement of the
external rectus muscle.
Tenotomy of the internal rectus consists in a
division of the tendon of this muscle at its inser-
tion into the globe. The eye then rotates out-
wards to an uncertain degree. This outward
rotation usually tends to increase as time goes on.
The eye also falls forward to a slight extent, so
that the tenotomised eye is more prominent than
its fellow and its palpebral fissure wider. A per-
manent weakness of inward rotation (adversion)
of this eye is also produced.
In order to advance a muscle, the tendon is
separated from the globe at its insertion. It is
usually then shortened by removal of more or less
of the tendon and muscle. The cut end of the
muscle is then secured to the globe at a point
further forward, nearer the cornea than its original
insertion. By a properly performed advancement
the eye is rotated to exactly the extent required.
The results obtained by the advancement opera-
112 THE TREATMENT OF
tion described in chapter xii. are permanent,
tending- neither to increase nor to decrease with
time. Both the power and extent of the rotation
of the eye in the direction of action of the
advanced muscle are increased. The rotation of
the eye in the opposite direction is not in any
case weakened in force, though in extreme cases
its extent may be slightly diminished. If the
abnormal convergence does not exceed 20 or 25°,
its cure by advancement of the external rectus
muscle rarely causes any noticeable degree of
retraction of the globe. If the deviation be of
higher degree than this, I usually combine the ad-
vancement of the external rectus with tenotomy of
the internal rectus, in order to avoid any retraction.
The operations on the external ocular muscles
are fully described and discussed in chapter xii.
The question may naturally be asked : "As the
deviation in a case of convergent squint is not
due to a defect of the muscles, why should one
ever seek to remedy this deviation by shortening
a muscle ?" The answer is this — In the presence
of a defect of the fusion faculty, refractive error
may cause a deviation, or the equilibrium of the
convergence centre may, in some unknown way,
be upset by a fright, blow on the head, whooping-
cough, &c. If one is able to train the fusion
sense early, the desire for binocular vision is,
more often than not, in itself sufficient to over-
come the deviation and produce a perfect cure, in
CONVERGENT SQUINT I I 3
spite of any adverse influences. In many cases,
optical correction of refractive error causes the
deviation to disappear. In other cases, as one
cannot act directly upon the nervous centre which
reerulates convergence, one has to be content to
act upon the peripheral motor organs. Take an
illustration — One is driving a pair of horses.
Suppose the off-side horse has a habit of boring
to the left. If any cause can be found (such as
sore shoulder), one may cure the habit by remov-
ing this cause. If not, it is a reasonable proceed-
ing to overcome his " deviation " to the left by
shortening the off-side branch of the right rein.
The angle of the deviation is measured at
each visit. If the measurements show a steady
decrease, of course, no operation is indicated
under any circumstances. In the case of a young
child whose fusion sense I have succeeded in
developing by means of the amblyoscope, if the
deviation does not decrease at a reasonable rate
I have recourse to operation. If the angle of the
squint is not higher than 20 or 25 , I advance
the rectus externus muscle without tenotomising
the internus. If the degree is higher than this, I
tenotomise the internus at the same time, not
because all the rotation required cannot be pro-
duced by advancement alone, but in order to
avoid retraction of the globe. This child's eyes
having been put approximately straight, his
trained fusion sense finds its expression in the act
114 THE TREATMENT OF
of binocular vision, and a perfect and permanent
cure results.
In a case in which I expect to get binocular
vision, I never perform tenotomy of the rectus
internus except in combination with advancement
of the externus. I once used to do so in hospital
practice, occasionally, for want of beds. Some
of these patients have since suffered from insuf-
ficiency of convergence, and pain in the eyes in
near vision. In two or three cases, in which
tenotomy was followed by divergence, I have had
to advance the tenotomised muscles. It very
rarely happens that any evil consequences follow
tenotomy of the internal rectus when combined
with advancement of the external rectus in high
degrees of squint. Perhaps this is because only a
small part of the total rotation is produced by
the tenotomy, the advancement of the opponent
muscle immediately tightening up everything and
correcting any tendency to proptosis.
If there is no hope of getting binocular vision,
so that cure of the deformity is all that can be
accomplished, I prefer not to operate until I am
able to do so under cocaine. The eyes are then
put exactly "straight" by advancement of the
external rectus muscle of the deviating eye, with
or without tenotomy of the internal rectus of this
eye. One not infrequently sees a patient whose
rectus internus has at some previous time been
tenotomised, producing proptosis of the eye, but
CONVERGENT SQUINT 115
still leaving some degree of convergent squint.
In this case an accurately performed advance-
ment of the external rectus will cure the devia-
tion, and at the same time draw the eye back
into its proper position in the orbit.
Simple tenotomy is an unsatisfactory opera-
tion, even in cases in which binocular vision is
out of the question. The tendon is divided, and
the result cannot in any individual case be fore-
told. Some cases turn out well, others do not.
The effect produced by a tenotomy is, on an
average, about 13 , though it varies very widely in
different cases. The effect, as a rule, increases for
the first three or four months after the operation,
after which it usually remains about stationary.
But in some cases, however skilfully the tenotomy
may have been performed, its effect continues to
increase for years, until a divergent squint is
produced — a more hideous deformity than that
which the operation was intended to cure.
There is one condition in which simple tenotomy
is sometimes advisable. One occasionally sees a
patient whose eyes in distant vision are normally
directed, but who turns in one or other eye to an
extreme degree in looking at a near object, even
in the absence of uncorrected refractive error.
One has no means of diminishing the excessive
activity of his nervous centre for dynamic con-
vergence, but the case may be treated empirically
by tenotomy of an internal rectus.
I I 6 THE TREATMENT OF
The internal rectus should never be tenot-
omised in any case in which dynamic conver-
gence is subnormal.
A patient requires very little care after the
operation of tenotomy. This is a great advan-
tage in a crowded hospital clinic. But I think
tenotomy owes its popularity chiefly to the
extreme facility of its execution, almost no special
knowledge being required. An accurately per-
formed advancement, on the other hand, is one
of the most delicate (and satisfactory) operations
in surgery.
Alternating convergent squint. — The treatment
of an accidentally alternating squint is similar to
that of a unilateral squint, except that there is
no acquired amblyopia to be remedied. It must
not be forgotten, however, that such a case, if
neglected, may become unilateral, and that the
deviating eye may then become amblyopic.
Essentially alternating squints are, fortunately,
not very common. The treatment consists in
optical correction of any ametropia which may be
present, followed, in the majority of cases, by
operation. Fusion training is impossible, as there
is a total congenital absence of the faculty of
acquiring fusion. For this reason, if operation be
required, I postpone it until the patient is old
enough to permit its performance under a local
anaesthetic.
Occasional convergent squint. — The majority of
CONVERGENT SQUINT I I 7
occasional squints in young children are of the
premonitory variety. Optical correction of any
refractive error which may be present usually
prevents the recurrence of the deviation, and so
allows the natural development of the fusion sense
to proceed.
Quite half the cases which are commonly
supposed to be occasional squints, occurring in
older children and adults, are really examples of
esophoria (see chapter xi.).
If one whose fusion faculty is perfect suffers
from anisometropia of so high a degree as to
render the act of binocular vision difficult, he will
be likely to manifest an occasional squint. Glasses
should be ordered which give the sharpest vision
in each eye, even though one eye be hyper-
metropic and the other myopic. The patient will
soon become accustomed to the inequality in the
size of the two images. An occasional squint
may be caused by hypermetropia in a patient
whose fusion sense is feeble.
Vertical deviation. — If operation be required
in a case of true vertical deviation, this should
consist in advancement of the inferior rectus
muscle, or complete central tenotomy of the su-
perior rectus, of the eye which turns up. The
inferior rectus should never be tenotomised.
Apparent vertical deviation (p. 37) requires no
treatment beyond that of the constant squint.
n8
CHAPTER VIII.
THE METHOD OE TRAIN I XG THE FUSION
SEXSE.
For more than half a century attempts have,
from time to time, been made to teach squinting
patients to use both eyes together, by means of
exercises with some form of stereoscope. Among
the stereoscopes used for this purpose are Wheat-
stone's original instrument, Brewster's and Helm-
holtz's stereoscopes, Hering'shaploscope, Holme's
stereoscope, and, more recently, Javal's " Stereo-
scope a cinq mouvements," Priestley Smith's
" Heteroscope," Landolt's and Parinaud's stereo-
scopes, and very many other more or less similar
instruments. Most of these are so arranged that
they can be adapted to suit the angle of the
patient's squint. But the proportion of cases in
which they can be used is very small, owing to
the suppression of the vision of the patient's
deviating eye. J aval attempted to overcome this
suppression by prolonged occlusion of one or
other eye, in the hope that, when at last both eyes
were uncovered, the patient might have diplopia.
All these instruments are intended for the use of
patients who are old enough to intelligently follow
the directions given them.
FUSION TRAINING 119
Probably most ophthalmic surgeons have, at
some time or other, been in the habit of ordering
" stereoscopic exercises " in cases of convergent
squint, and have, after careful trial, given them
up as useless. The reason of their failure is the
very early age at which the fusion sense normally
develops. Fusion training, to be of any material
benefit, must be undertaken within this normal
period of development.
Fusion training of young squinters under five
years of age is in suitable cases, quickly and
easily accomplished, and the results obtained are
most striking and gratifying. Between five and
six the treatment is apt to take longer, and the
results to be less perfect. After the age of six
or, at the latest, seven years, the results are, from
the patient's point of view, not worth the time
and trouble which they cost.
There are two great difficulties in the way of
fusion training in the case of young children : —
(i) Though the visual acuity of the child's
deviating eye may perhaps be perfect, the vision
of this eye is suppressed, so that he is ordinarily
unable to receive impressions from it except when
the other eye is closed.
(2) The child is far too young to understand
the purpose of fusion training or to follow the
directions of the surgeon. He will, therefore,
only permit the exercises so long as he finds
them attractive and interesting.
120 FUSION TRAINING
After many experiments, I devised an in-
strument with the help of which I have to
a great extent succeeded in overcoming these
difficulties. I have called it "amblyoscope" —
an instrument by means of which a non-seeing
eye is trained to take its share in vision. The
amblyoscope has retained its present form since
1895.
The Amblyoscope^ — The instrument consists of
two halves joined together by a hinge. Each half
consists of a very short brass tube joined to a
longer tube at an angle of 120 . At the angle of
junction of the tubes is an oval mirror, 2 protected
on the outside by an oval plate of brass. Each
half of the instrument has at its distal end an
object-slide carrier, and at its proximal end a
convex lens having a focal length of five inches
— the distance of the reflected image of the object-
slide. In front of each lens is a slot into which
a prism, axis vertical, may be inserted if required.
The diameter of the tubes is \\ inch.
1 The amblyoscope is made by Mr. Hawes, optician,
79, Leadenhall Street, London, E.C., and by the principal
manufacturing opticians in England and abroad.
2 The mirrors must be extremely thin. If they are merely
pieces of ordinary thick mirror glass there will be blurring,
owing to reflection from the surface of the glass as well as
from that of the mercury. Mirrors silvered on the surface
answer well but are easily scratched. I have tried polished
speculum metal. This is satisfactory but very expensive.
The mirrors must be accurately set perpendicular to the
plane of the tubes.
FUSION TRAINING
121
A brass arc 1 connects the two parts of the
instrument, being clamped on one side by a bind-
ing screw set in a long slot and on the other by a
binding screw set in a short slot. When the screw
in the long slot is loosened, the two parts of the
instrument can be brought together to suit a con-
vergence of the visual axes up to 6o°, or separated
to suit a divergence of as much as 30 . When
this screw is tightened and the screw in the short
slot loosened, an amplitude of movement of about
io° only is permitted.
The convex lenses of course render unnecessary
any adjustment of the instrument for the patient's
inter-pupillary width.
1 In the earlier forms of the instrument I had the arc
marked in degrees, as I thought that the instrument might
also be used for the subjective measurement of hetero-
phorias. I found, however, that it was of no use for this
purpose. No instrument, in which the objects looked at
are near the eyes, is reliable for measuring heterophoria.
Though the lenses render accommodation unnecessary, the
patient unconsciously accommodates for an object which he
knows is near.
122
FUSION TRAINING
Illumination of the object-slides. — Each object-
slide is illuminated by a separate electric lamp.
A stout brass rod, about two feet in length, is
held in brass sockets at each end. The brass
sockets are screwed to a board, which is firmly
^Q> ©
I
!
1,
1
it ^
1
1
|
/
o K
Jy q
Fig.
secured to the wall of the consulting room in such
a position that the brass rod is vertical. A brass
collar slides up and down the vertical rod, and is
fixed by a thumb-screw at the height required.
This collar supports two independent collars, each
of which has attached to it a long horizontal arm.
Each of these arms is four feet in length, and is
FUSION TRAINING I 23
free to move in a horizontal plane independently
of the other. An electric lamp is suspended under
each horizontal arm from a ring which slides along
the arm. The illumination of either of the object
slides in the amblyoscope may be separately in-
creased or diminished by bringing its lamp nearer
or pushing it further away.
Before I had electric light I used two paraffin
lamps on a table, varying the distance of each
lamp and the height of the flame as required.
This simple plan answers just as well but is not
quite so convenient.
The object-slides.— -Fig. 13 shows the familiar
vertical slits with their control marks. They are
not used for fusion training, one could not induce
a young child to study such uninteresting objects.
They are shown because they are useful in making
experiments with older persons.
The devices used in fusion training are of three
classes : —
( 1 ) Those which do not require any blending
of images, but only simultaneous vision of dis-
similar objects with the two eyes. Fig. 14,
showing a cage on one slide and a bird on the
other, is an example. Other pairs of devices of
this class are a clown and a hoop, a mouse and a
trap, a clock-face and hands, &c.
(2) Devices of the second class, of which figs.
16 and 17 are examples, require true fusion of
images in order that the full picture may be seen.
I2 4
FUSION TRAINING
Fig. 13.
Fig. 14.
^w
m n
11
FUSION TRAINING
125
Fig. 16.
Fig. 17.
Fig. 18.
126 FUSION TRAINING
The pictures on each pair of slides are exactly
similar, except that part of the design is omitted
in one and a different part in another. For
example, in fig 16 a leg is omitted in one slide
and the hat in the other. A child who blends
the images sees a man with two legs and a
hat.
(3) Devices such as fig. 18 can only be appre-
ciated by patients who have the third grade of
binocular vision, the sense of perspective.
The designs are drawn on ij inch squares of
thin translucent paper. The paper is then pasted
on squares of glass. There is no difficulty in
making designs of the first class. Object slides of
the second class are made as follows : — I draw, on
pieces of paper 1^ inch square, rough, simple
pictures, such as a horse, a clown, a cow, a man
with a hat and pipe, &c, the more grotesque the
better the children seem to like them. I then
make two tracings of each on the translucent
paper, omitting a different part of the picture in
each tracing. 1
Ftision Training. — The education of the fusion
1 " Stereoscopic views" are of no practical use whatever
for fusion training. But I once had made some tiny trans-
parent stereoscopic photographs to fit the amblyoscope.
My idea was that a child who wearied of my own artistic
efforts might be shown some of these views, occasionally,
by way of a change. But I found that young children took
no interest in them. They much preferred simple pictures
which they could understand.
FUSION TRAINING I 27
sense should be undertaken at the earliest possible
age. I repeat this because it is of supreme import-
ance—the only key to success. In the case of a
child of average intelligence, it is quite easy to
use the amblyoscope at the age of three to three
and a half years. I have succeeded in many cases
before three years of age, but it is often rather
difficult to keep the attention of these very young
children.
The deviating eye must not be too blind. In
cases which have received efficient treatment since
soon after the first appearance of the deviation,
the vision of each eye is nearly always perfect.
But, in neglected or inefficiently treated cases, the
deviating eye is often very blind. (Compare
Tables III. and V., pp. 76 and 77). I do not as
a rule attempt fusion-training in a child who,
after all possible means have been employed to
restore the sight of the deviating eye, is still
unable to see the 1 inch ivory ball at six yards.
A squinter sees with his fixing eye only, or,
under certain circumstances, with the deviating
eye only, but not with both simultaneously. The
first step in the treatment is to overcome this sup-
pression. If the child has any refractive error this
is corrected by spectacles. It occasionally happens
that the mirror test (p. 80) has revealed a slight
vertical deviation. In this case corresponding
prisms, axes vertical, are inserted in the slots in
front of the lenses. Seated in a chair facing the
128 FUSION TRAINING
lighting apparatus, I take the child on my knee
and adapt the amblyoscope' roughly to the angle
of his squint. I put in the instrument first a pair
of object-slides which requires no fusion, only
simultaneous perception — those shown in fig. 15,
for example. Each light is at first about 4 feet
away from its object slide. Suppose the cage is
before the fixing eye and the bird before the
squinting eye. The child, on looking into the
amblyoscope, will see only the cage. I tell him
to look for the bird, while I bring the light before
the deviating eye nearer and nearer. At last a
point is reached when the illumination of the
object-slide before the deviating eye becomes so
intense that the vision of this eye can no longer
be suppressed. The child suddenly says he sees
the bird he was told to look for. But he has now
usually lost sight of the cage before the fixing
eye. The relative distances of the lights are
then readjusted until, after a few minutes of
alternation of the vision of the two eyes, the child
sees the bird and the cage simultaneously. The
child is then allowed to grasp the amblyoscope
1 I used occasionally to drop the instrument and break
some part of it, until Dr. Ernest Maddox suggested the
simple expedient of slinging it from the ceiling by means of
a string and pulley and little leaden counterpoise. Since
then there have been no mishaps. When pulled down
ready for use the amblyoscope hangs about 3ft. away from
the wall-bracket which supports the lighting apparatus.
FUSION TRAINING I 29
with both hands, while I, putting my hands over
his, converge and diverge the two halves of the
instrument, in order to make the bird appear to go
in and out of the cage. Other similar pairs of
object-slides are then shown. The child soon
learns to move the instrument himself, so as to
put the bird in the cage, the cat on the chair, the
clown in the hoop, &c. One must talk to the child
all this time, as it is only by encouraging him to
chatter that one learns what he really sees.
A pair of slides requiring fusion of images is
now shown — fig. 16, for example. The child at
first sees two men, each picture being imperfect.
Soon a position is found in which the child sees
one man having two legs and a hat. The bind-
ing screw in the long slot is now tightened and
that in the short slot loosened, so that the
amplitude of movement between the two halves
of the amblyoscope is restricted to about io°.
Other pairs of slides requiring fusion of images
are successively shown the child, and he is en-
couraged by one's remarks to examine every part
of the fused picture. After a time it is found
that the angle of convergence of the instrument
may be varied slightly without the fused picture
coming to pieces. The child has now, under
these special conditions of illumination and con-
vergence, the second grade of binocular vision,
— true fusion with some amplitude.
The next step is to increase the amplitude of
130 FUSION TRAINING
fusion. The intensities of the lights and the
angle of convergence of the amblyoscope are
arranged as before. Devices requiring fusion,
such as figs. 16 and 17, are shown. An attempt
is made to gradually diverge and converge the
two halves of the instrument, more and more,
while the child is examining and talking about
the various pictures shown him. After some
practice, in the case of a young child, a con-
siderable range of movement becomes possible,
fusion being still maintained. This "amplitude
of fusion " may, for practical purposes, be taken
as a measure of the extent to which the fusion
faculty has been developed.
A child who has any considerable amplitude
of fusion will nearly always be found to have
acquired the third grade of binocular vision also
— the sense of perspective. The slides, fig. 18,
are shown, and the child is asked whether he is
looking at the outside or the inside of the tub.
He will at once say " the inside." If these slides
are now changed from one tube to the other, he
will see the tub bottom up.
The child having now acquired the highest
grade of binocular vision under these special
conditions of illumination and convergence, the
next step is to gradually equalise the light before
the two eyes. This may readily be done, at this
stage, without a return of the suppression.
If the child be young enough, a very powerful
FUSION TRAINING I 3 I
"desire for fusion" may usually be created in
five or six lessons, given at intervals of one week.
It must be remembered that the prime object
of these exercises is the training of the fusion
sense at a time when this may be successfully
accomplished — not a mere remedying of the
deviation. In many cases, however, the powerful
" desire for fusion " thus established, directly
brings about a sudden cure of the squint. In the
larger group of cases, in which optical correction
of refractive error is depended upon to lessen, and
perhaps overcome, the deviation, there is no
danger of the newly-acquired faculty of fusion
being lost meanwhile. If even a faint degree of
fusion sense has once been acquired, its persis-
tence is truly remarkable. No matter how many
years binocular vision may be in abeyance, it
seems as difficult to forget as the art of swim-
ming. If the periodic measurements of the angle
of the deviation show that this is not decreasing
reasonably quickly under optical treatment, I have
no hesitation in operating at any age, by advance-
ment of an external rectus, with or without teno-
tomy of the rectus internus. The eye being put
approximately "straight," the "desire" for bi-
nocular vision fills up any slight gap that may
remain, and a perfect cure results.
Fusion training, in the case of these young
children, must be carried out by the surgeon him-
self. It is of no use giving the amblyoscope, or
I3 2 FUSION TRAINING
any other instrument, to the mother for use at
home.
In the case of older children, I have often, by
way of experiment, ordered some form of stereo-
scope, or Cuigriet's (or Javal's) " lecture con-
trolee " for home use. I have not, in any single
instance, seen any good result therefrom. A
child who is old enough for " stereoscopic exer-
cises " and "bar reading" is far past the age
when the fusion sense might have been developed.
Similarly, if he has suffered from neglected con-
stant unilateral squint since infancy, it will now
almost certainly be impossible to remove the
acquired amblyopia of the squinting eye, though
it might easily have been done at an earlier age.
In this description of fusion training I wish to
draw attention rather to the principles than to the
instruments by the help of which they have been
defined and applied. Though these methods
have been constantly employed for many years,
it is possible that they may be improved upon ;
but the principles are unalterable.
*33
CHAPTER IX.
DIVERGENT SQUINT.
Comitant divergent squint presents two distinct
varieties differing widely in their pathology,
appropriate treatment and prognosis. They may
be called, respectively, myopic and neuropathic.
Myopic Divergent Squint.
The divergence most frequently first makes its
appearance at about ten or twelve years of age.
It may be either unilateral or alternating, more
commonly the former. Usually the patient is
known to have been short-sighted for four or five
years, and the short-sightedness has been increas-
ing, until, at the time of the appearance of the
divergence, there is myopia of perhaps 5 or 6 d.
or more. As a rule the fusion sense is well-
developed, though I have sometimes found it
deficient. The deviation is seldom constant ;
at one moment the eyes may be " straight " and
the patient have binocular vision ; a few minutes
later one or other eye may exhibit a high degree
of divergence. Myopic divergent squints of low
degree are rare.
10
134 DIVERGENT SQUINT
From observing and carefully questioning many
of the more intelligent patients, I conclude that
the usual mode of origin of a myopic divergent
squint is as follows : — Soon after the child begins
school it is found that he is not easily able to see
the black-board. He is given a front seat where
he can see, and nothing more is done. A few
years later, say at twelve or thirteen years of age,
the myopia has increased so as to bring his far
point very near his eyes. All distant objects are
blurred. In reading, he has to hold his book so
near his eyes that it becomes very difficult to con-
verge steadily to the required extent. He com-
plains that "the words run into each other" and
he soon tires. One frequently hears that, at about
this time, he discovered that, by covering one eye
with his hand, he could read quite comfortably
with the other. In any case, he gives up the
struggle and allows one eye to wander outwards,
while he reads without effort with the other. At
first there is no actual divergence — only a failure
to converge while the other eye is engaged in
near vision. But, as a result of convergence
not being used, the function becomes weakened,
so that either eye diverges when screened or when
the other is being used in near vision. When
the myopic eye has become divergent there is no
diplopia in reading, even though the fusion faculty
be perfect, because the divergent eye is directed
towards the misty distance. When the patient
DIVERGENT SQUINT I35
looks up from his book, the divergent eye at first
always recovers itself. After a time, as the habit
becomes confirmed, this eye often remains widely
divergent in distant vision. The picture of distant
objects formed in the fixing eye is already blurred
and indistinct, so the very faint eccentrically-placed
image formed in the divergent eye causes no
tendency to fusion. But when the divergent eye
partially recovers its normal direction, so that it
receives a more centrally-placed image of the
object to which the fixing eye is directed, the
desire to blend these two blurred images causes
the eyes to become straight. This probably
explains why in a case of myopic divergent squint,
the eyes are sometimes straight, sometimes widely
divergent, but scarcely ever' divergent to a slight
degree.
The treatment of a case of myopic divergent
squint consists in exactly correcting the myopia
and myopic astigmatism. The patient should
wear the glasses always, both for near and distant
vision. Patients at first complain that the glasses
make print appear very small. Children soon
become accustomed to them. But myopes who
first begin to wear glasses in adult life, in some
cases, require a second pair of glasses for near
vision, 1 d. or 2 d. weaker than the distance
glasses. Their power of accommodation has
become feeble, for want of exercise. Glasses
with which the patient can see distinctly usually
] $6 DIVERGENT SQUINT
cause a rapid disappearance of the squint, in fairly
recent cases, and frequently even in cases which
have lasted for many years. But it often happens
that the prolonged disuse of the function of
dynamic convergence weakens the static conver-
gence, so that this becomes a negative quantity,
and a tendency to divergence remains. While
both eyes are open and the glasses are worn, the
fusion faculty prevents any deviation, but if one
eye be shaded for a moment it may diverge and
remain divergent for a second or two after the
removal of the shade. Operation is rarely neces-
sary. But in some cases, usually of long standing,
in which the static convergence remains very
deficient, advancement of an internal rectus adds
greatly to the patient's comfort.
It must not be forgotten that the case may be
complicated by muscular exophoria.
Infantile myopic divergent squint, excluding
cases of buphthalmos, is very rare. I have notes
of only seven cases. These cases differed from
unilateral convergent squints only in the kind of
refractive error and the direction of the deviation.
The treatment was similar to that employed in
convergent squint.
Neuropathic Divergent Squint.
The divergence nearly always dates from in-
fancy. It may be constant or occasional, unilateral
or alternating. In the constant cases there is a
DIVERGENT SQUINT 137
total absence of the fusion sense. In the occasional
cases there is a feeble degree of binocular vision
when the eyes are "straight"; when an eye
diverges there is usually no diplopia. The refrac-
tion, as a rule, is normal. In the constant uni-
lateral cases there may be acquired amblyopia.
In other cases the vision of the eye is perfect.
The divergence varies greatly in degree, even in
a case in which it is constantly present. The
power of dynamic convergence is deficient. It
varies from time to time in an extraordinary
manner. One day, perhaps, the dynamic conver-
gence may be almost normal ; a few days later
the most persevering efforts may fail to elicit the
slightest movement of convergence. In these
neuropathic divergent squints, the association
between accommodation and convergence is
usually very slight. One not infrequently sees a
patient who can nearly always voluntarily correct
the faulty position of his divergent eye without
much effort, but who habitually allows this eye
to diverge while he is exercising say 4 or 5 d. of
accommodation in near vision. In young subjects
the power of rotation of each eye separately is
nearly always normal in every direction. In long-
standing cases, however, the power of independent
inward rotation is usually deficient.
The subjects of neuropathic divergence are
often bright, quick-witted, intelligent, but they are
nearly always very " nervous " and highly strung.
138 DIVERGENT SQUINT
One frequently sees the same ocular defect in
other members of the family. A family history
of epilepsy or insanity is very common. I find
neuropathic divergence more common in females
than in males, in the proportion of about 7 to 2.
The treatment of neuropathic divergent squint
is not satisfactory. There is seldom any notable
refractive error, and when there is, its correction
produces no effect upon the divergence. Attempts
at fusion training nearly always fail, however early
the patient may be seen. Practically one's only
recourse is operation. One or both internal recti
should be advanced (e.g., Case B, 166, p. 162).
The externi should be tenotomised at the same
time only when the power of abversion is dis-
tinctly greater than normal. If the power of
adversion is very markedly deficient, a musculo-
capsular advancement should be performed. In
a case in which divergence is not constantly
present and in which there is some slight degree
of fusion, advancement gives a satisfactory result
(e.g., Case B, 165, p. 161).
non-comitant divergent squints, other than
Paralytic.
Divergence in extreme myopia.- — In cases ot
progressive myopia of very high degree it is not
uncommon to find the visual axes divergent.
These cases differ entirely from ordinary myopic
divergent squints. They are non-comitant. The
DIVERGENT SQUINT I 39
arcs of rotation of each eye are subnormal in every
direction. The divergence begins imperceptibly,
and increases slowly up to about 20 . It is
generally held that the divergence is caused
mechanically, by the egg-shaped eyes adapting
their long axes to the divergent positions of the
orbits. I believe this explanation to be correct.
Increased tension of the external recti does not
appear to be an important factor, as I have, in
three such cases, seen both these muscles teno-
tomised without result.
Divergence of blind eyes. —When both eyes are
blind they almost invariably diverge. When one
eye only is blind, its behaviour will depend, to a
great extent, upon the state of the refraction of
the seeing eye. If this is normal or myopic the
blind eye will, as a rule, diverge ; if it is markedly
hypermetropic it will usually converge.
If the refraction of one eye be normal, or nearly
so, while the other eye is very highly myopic, the
latter is, in the absence of optical correction,
practically a blind eye, and will behave as such.
In a case of convergent squint in which the
squinting eye has become very amblyopic, this
blind eye may become divergent in after years,
without any tenotomy having been performed.
Divergence secondary to tenotomy of an internal
rectus muscle. — As already explained, in a large
proportion of cases of convergent squint with
hypermetropia, the constant wearing of glasses
140 DIVERGENT SQUINT
gradually causes the visual axes to become less
convergent. It was formerly the practice to
tenotomise an internal rectus in almost all cases
of convergent squint, without going into the
question of refractive error. Such of the hyper-
metropes who subsequently took to wearing-
convex glasses to improve their vision, ran con-
siderable risk of divergence.
If tenotomy be performed only in cases in
which optical treatment has failed, the risk is
less. But even then a case of divergence will
occasionally be seen. In an ordinary tenotomy
the tendon and its lateral expansions are divided.
Usually the cut end of the tendon becomes con-
nected to its old insertion by an irregular band of
scar tissue, which may or may not subsequently
stretch. Tenotomy is called a " setting back " of
the tendon, because it is supposed that the tendon
becomes directly reattached to the globe further
back. I believe that this seldom happens after a
neatly - performed tenotomy. Sometimes the
tendon fails to become reattached to the globe at
all. In this case the surgeon may fail to find the
muscle unless he knows where to look for it. Its
anterior end will be found behind the sunken
caruncle, lying against the inner wall of the orbit
(see page 213).
I4i
CHAPTER X.
THE TREATMENT OF SQUINT.
I L L USTRA Tl I T E CA SES.
The following clinical notes, copied from my
squint case-books, will serve to further explain
the methods of treatment which I employ, and to
show the results which may ordinarily be expected
therefrom.
As a rule, it is only possible to get a perfect
result in a case in which efficient treatment is
commenced early. But, unfortunately, one sees
a very large proportion of the cases for the first
time after years of neglect, or perhaps inadequate
or even harmful treatment. I have, therefore,
also selected some examples of these old cases.
Case B, 23. February 4, 1896.— A boy, aged 2 years
11 months, was brought to me, suffering from conver-
gent squint. He had squinted for about ten or twelve
months. L. E. was convergent 28 . Fixation was
present in L. E., but the sight of this eye had de-
teriorated so much that, when R. E. was bandaged,
he could not find a white-handled penknife on the
floor, unless it was close to his feet. Abversion L. E.
was perfect. Ordered, atropine ointment, 1 per cent.,
thrice daily for both eyes, for retinoscopy.
February 11. — Convergent squint L. E. 32 with
142 TREATMENT OF SQUINT
atropine. Retinoscopy — each eye + 275 D. sph.
+ 0-5 d. cyl. ax. vert. Ordered spectacles + 2*25
D. sph. + 0*5 D. cyl. ax. vert., also guttas atropine
1 per cent, for R. E. only every morning.
March 3. — Child uses R. E. (atropised) in distant
vision, and L. E. (unatropised) in near vision. Con-
vergent squint L. E. 20 , with glasses. Ordered,
continue.
April 9. — Similar note. Convergent squint L. E.
1 7 . Ordered, continue.
May 29. — Child now uses (unatropised) L. E. and
turns in (atropised) R. E. always, both in near and
distant vision. Ordered, stop the drops, and come
again in one month.
June 18. — Squint nearly alternating, slight prefer-
ence for squinting with L. E. Convergent squint L. E.
1 6°. Ordered, atropine for R. E. only, every morning
for a month, then stop it and bring the child to me
two or three weeks later.
August 4. — C. S. alternating 14 . Fusion training
with amblyoscope. Child sees both images readily and
can sometimes blend them.
August 7. — Fusion training.
August 10. — Fusion training. Child blends images
readily.
August 14. — Fusion training. Child has considerable
amplitude of fusion. C. S. alternating 15 .
August 18. — Fusion training.
August 25. — No squint with glasses. The mother
says that the eyes have been straight since the last
lesson, though he lias turned the eye in, occasionally,
for an instant.
November 6. — Child never squints now with glasses,
though he occasionally does so without them, the
nurse says. No squint seen now either with or without
glasses.
October 8, 1897. — Child going on well. He never
squints now.
ILLUSTRATIVE CASES I 43
September 29, 1898. — Spectacles too small. Ordered,
repeat them.
June 13, 190 1. — (Aged 8 years 3 months). Ordered,
atropine for repetition of the retinoscopy.
June 20. — Retinoscopy each eye + 2*25 D. sph.
+ 0-5 D. cyl. ax. vert. Vision, each eye f. Ordered,
spectacles 0*5 D. lower than the retinoscopy, with per-
mission to take them off while playing games.
August 19, 1902. — The boy has only used his glasses
for school work since last visit, and never when out
of doors. He has not been seen to squint for years.
Case B, 18. November*], 1895. — A girl, aged 2 years
1 month, was brought to me, suffering from C. S. R. E.
33 . She had squinted since she had whooping cough
aged 1 year 4 months. She had central fixation in
R. E., but she evidently did not see well with it when
the L. E. was tied up. Abversion perfect. Bright,
intelligent girl, only child. Mother has C. S. R. E.
Ordered, atropine for retinoscopy.
November 13. — Retinoscopy R. E. + 175 D. sph.
L. E. 4- 1-25 D. sph. C. S. R. E. 26 , with atropine.
Ordered, spectacles 0*25 D. less than retinoscopy ; also
guttae atrophias 1 per cent., one drop in L. E. only,
every morning.
December 11. — Child uses R. E. (unatropised) in
near vision, and L. E. (atropised) in distant vision.
Ordered, continue.
February 6, 1896. — Same. Ordered, continue.
April 2. — Child uses R. E. (unatropised) now, both
in near and distant vision, and squints with atropised
L. E. C. S. L. E. 27 . Ordered, stop atropine.
June 4. — Squint alternates 22 . Fusion training
with amblyoscope : child readily sees both images, but
I cannot be certain that she blends them.
June 10. — Fusion training : child learned to blend
images quite easily.
144 TREATMENT OF SQUINT
June 19. — Fusion training.
July 1. — Fusion training.
July 7. — Fusion training. Child now has an ampli-
tude of fusion, with the amblyoscope, of io° to 15 .
C. S. alternating 23 . As the fusion faculty is well
developed and the deviation is stationary, I advised
operation, especially as, in view of the insignificance
of the refractive error, spectacles can be dispensed
with. The parents preferred to wait until the child
was 3 years old. Child's fusion was exercised with
the amblyoscope once a month until
October 5 (aged 3 years). — C. S. alternating 22 . I
advanced the right external rectus muscle, under
chloroform. (I employed the method described in
Chapter XII.).
Case dressed every day.
October 12. Sutures removed.
November?,. — R. E. is not opened quite so widely as
L. E., and there is still some redness of the conjunctiva.
There is no squint now, and the child has perfect
binocular vision. She, of course, has not worn her
glasses since the operation.
I saw the little girl in January, 1897, October, 1897,
June, 1899, and again on
November 12, 1902. — I wrote and asked the mother
to bring her to me. The child is now nine years old.
She has § vision, each eye, and perfect binocular vision.
She only dimly recollects that she ever had anything
the matter with her eyes.
Case B. 192. November 20, 1899. — A lady, aged
23 years. History — she began to squint with the
L. E. when she was about 1 year old. She was treated
from time to time with "drops." At about 4 years
of age she was ordered glasses. She has worn glasses
ever since. When she was 8 years old the L. E., was
operated upon (tenotomy).
ILLUSTRATIVE CASES I 45
She now has convergent squint L. E. i6° both with
and without her glasses. Vision of R. E., with glasses,
is §. L. E. has lost central fixation, and with it she
can just count fingers close to her face. As the result
of the tenotomy, the L. E. is prominent and the caruncle
sunken. Retinoscopy under homatropine — R. E. +
i D. cyl. ax. vert., L. E. + 175 D. cyl. ax. 70 down
and out, at approximate macula. The blindness of
the left eye is now, of course, quite incurable. She
wishes to have something done to remove the deformity.
December 5. — I advanced the left external rectus
muscle, under cocaine (by the method described in
Chapter XII.).
December 20. — There is a little redness remaining
from the operation. The eyes are quite " straight,"
and the advancement has had the effect of replacing
the L. E. in its proper position in the orbit. Ordered,
rigid pince-nez + 1 D. cyl. ax. vert.
June 14, 190 1. — Eyes quite normal in appearance,
both with and without the glasses.
Case D, 318. April 13, 1900.— Boy, aged 1 year
5 months, seen at Moorfields Hospital. The mother
said he had measles in February and he " has squinted
the last few weeks." C. S. R. E. 37 . Steady central
fixation R. E. Ordered atropine, for retinoscopy.
April 24. — C. S. R. E. 32 under atropine. Retino-
scopy R. E. 4- 5-5 D. sph. L. E. 4- 4*5 D. sph. Or-
dered, spectacles R. E. 4- 5 D. L. E. 4- 4 D. Guttae
atrophias 1 per cent, to be put in L. E. only every
morning.
May 8. — Child uses (unatropised) R. E. and squints
(atropised) L. E. always. Ordered, stop drops.
June 5. — Squint alternates, 21 .
August 7. — No squint while wearing glasses. C. S.
R. E. about 20 without glasses.
September 10, 1901. — Glasses too small now, repeat
them.
I46 TREATMENT OF SQUINT
November 7, 1902. — No squint seen here either with
or without glasses. He is said to turn in R. E. some-
times when his glasses are taken off at bedtime.
Case A., 489. May 10, 1900. — Boy, aged 3 years
4 months, seen at the West Ham Hospital. C. S.
L. E. 34 . Fixation L. E. was lost. Abversion L. E.
full. The mother said he had "squinted on and off
for about a year." Ordered, atropine for retinoscopy.
May 17. — C. S. L. E. 27 with atropine. Retino-
scopy — R. E. 4- 375 D. sph. + 075 d. cyl. ax. 25
down and out. L. E. approximately the same. Or-
dered, spectacles for constant wear, R. E. 4- 3-5 D.
sph. 4- 075 D. cyl. ax. 25 down and out. L. E. 4-
3-5 D. sph. pro tern. : also R. E. to be occluded by a
gauze pad secured by strapping plaster, for one month.
June 14. — Steady central fixation L. E. Ordered,
guttae atropinae 1 per cent, for R. E. only every morn-
ing for one month.
July 12. — Child now uses (atropised) R. E. in distant
vision, and turns in L. E. In near vision he uses
(unatropised) L. E., and turns in R. E. C. S. L. E.
23 . Ordered, continue.
August 30. — Child uses R. E. distant vision and L. E.
near vision. When glasses are taken off, he always
fixes with L. E. and turns in the (atropised) R. E.
Ordered, continue.
October 25. — Child uses (unatropised) L. E. and turns
in the (atropised) R. E. always, both with and without
the glasses. Ordered, stop the atropine and return in
one month.
December 6.— C. S. L. E. io°. The child uses L. E.
almost as readily as R. E. Fusion training with
amblyoscope.
December 13. — Fusion training.
December 20. — Fusion training. Child blends images,
but with difficulty.
January 10, 1901.— Fusion training.
ILLUSTRATIVE CASES I 47
'January 24. — Fusion training. Images blended at
once. A fair amplitude of fusion.
February 7. — No squint with glasses.
July 11. — No squint with glasses. When glasses
are taken off the child has no squint, as a rule ; but
when he is told to look at a picture L. E. turns in
about 35 to 40 , and he says he sees two books (he
volunteered this statement without any questioning).
May 29, 1902. — Child never squints now. Ordered,
atropine for both eyes for repetition of the retinoscopy.
June 7. — Retinoscopy, R. E. + 3"5 D. sph. + 075
D. cyl. ax. 30 down and out. L. E. + 3-5 D. sph. + 1
D. cyl. ax. 30 down and out. Vision with these glasses
R. E. I, L. E. f . Ordered, spectacles 0*5 D. less than
the retinoscopy.
Case D, 832. May 6, 1902. — A boy, aged 9^ years,
was brought to the Royal London Ophthalmic Hos-
pital, because he could not see with the right eye. The
father said that the boy squinted when he was teething.
He was taken to an eye hospital where he was given
ointment (probably atropine) for both eyes for about
a year. At about 3^ years of age he was given glasses.
The glasses gradually " cured the squint but the sight
of the eye, which used to squint, is almost gone."
The boy is wearing + 4 D. sph. each eye. Vision
with his glasses — R. E. counts fingers at two feet,
L. E. §. Fixation R. E. is, of course, lost. He has
C. S. R. E. 4 , with his glasses. Abversion R. E. full.
Ordered, atropine for retinoscopy.
May 9. — Retinoscopy L. E. -f 4 D. sph. + id. cyl.
ax. vert. R. E. approximately the same. Vision with
glasses — R. E. not improved, L. E. f. Ordered, spec-
tacles 0*5 D. less than retinoscopy. The blindness is
now of so long standing that it would be quite hopeless
to attempt to restore the sight of the R. E.
Case A, 58. April 23, 1894. I saw a girl, aged
I48 TREATMENT OF SQUINT
2 years 3 months. Alternating C. S. about 30 . She
had squinted since early infancy.
April 26, 1894. — Retinoscopy under atropine. — Each
eye 4- 1*5 D. sph. Ordered, 4- 1*25 D. sph.
November j, 1895. — C. S. alternating 32 . Attempted
fusion training with amblyoscope.
During November, 1895, I made six attempts to
train the child's fusion sense. Though she was a
tractable and intelligent child, I did not succeed in
getting even simultaneous perception of the object
slides. She could see one picture or the other, but
she could not see both together. (Case of essentially
alternating squint, with total absence of the fusion
sense.)
August, 1900. — The girl came to me at the West
Ham Hospital. She has not worn the glasses for two
or three years. Two years ago she went to another
hospital, where the right internal rectus muscle was
tenotomised. C. S. alternating 19 now. Vision fi
each eye.
October, 1900. I advanced the right external rectus
muscle, under cocaine.
November 8, 1900. — The eyes are " straight " and
normal in appearance. The vision of each eye sep-
arately is perfect. But of course she can neve:
have binocular vision. No glasses required.
Juue 12, 1902. — Eyes normal in appearance, patient
comfortable.
Case B, 3. — May 22, 1893. I saw a girl, aged 1 year
5 months. She had C. S. R. E. about 35 . She had
squinted for six or seven months. R. E. has not lost
the power of central fixation. Ordered, atropine for
retinoscopy.
May 25. — Retinoscopy each eye + 4 D. sph. Or-
dered, glasses each eye 4- 3'5 £>• sph. : also, gutta*
atropine 1 per cent. L. E. only every morning.
June 26, 1893. — Glasses worn well. When the child
ILLUSTRATIVE CASES 149
is induced to look at anything close to the eyes, she
uses the R. E. (unatropised) and turns in the (atropised)
L. E. At other times she has C. S. R. E. about 30 .
Ordered, continue drops for L. E. only.
July 28.— Child uses L. E. (atropised) in distant
vision and R. E. (unatropised) in near vision. When
glasses are taken off, she always uses R. E. and squints
with (atropised) L. E. Ordered, continue.
September 5.— Child always uses R. E. and squints
with the (atropised) L. E. both in near and distant
vision. Ordered, stop the atropine.
April 23, 1894.— C. S. nearly alternating. More
often fixes with the R. E., which was at first the squint-
ing eye. C. S. 21 .
November 6th, 1895. — Owing to my absence abroad
the child was left much longer than she should have
been. C. S. L. E. 13 . Ordered, atropine for repeti-
tion of retinoscopy.
November 13. Retinoscopy + 3-5 D. sph. + 0-5
D. cyl. ax. vert, each eye. Ordered, glasses 0*5 D. less
than the retinoscopy. As the child now squinted
constantly with L. E. (the originally fixing eye) I
ordered atropine to be put in the R. E. only every
morning.
November 27.— She uses R. E. (atropised) in distant
vision and L. E. (unatropised) in near vision. Ordered,
continue.
December 20. — Child now uses L. E. almost always
in preference to the (atropised) R. E. Ordered, stop
atropine.
January 15, 1896.— C. S. nearly alternating n°.
Fusion training.
January 20. — Fusion training.
January 27. — Fusion training. Child blends images.
February 4. — Fusion training. Child has some am-
plitude of fusion.
February 13. — Fusion training. Considerable ampli-
tude of fusion.
11
15O TREATMENT OF SQUINT
February 20. — Child has frequently said that she
sees two faces, &c., since last visit. Fusion training.
February 27. — No squint.
June 5. — No squint with glasses. C. S., with dip-
lopia, when glasses are taken off. Diplopia is so in-
tense that the little girl remarks it at once.
October 19, 1898. — Glasses too small. Ordered,
repeat the glasses, with larger frames. The child is
never seen now to squint. Vision R. E. £, L. E. (the
originally fixing eye) § easily, | partly.
October 24, 1902. — At my request, the mother brings
the child (aged now 9 years 10 months) to me again
for examination. She has grade III. binocular vision,
with a good amplitude of fusion. She never squints
now, either with or without her glasses. She must
always wear glasses, of course, on account of her
refractive error, but I have given her permission to
dispense with them during her dancing lessons and
gymnasium practice.
CASE A, 437. January 18, 1900. — I saw a boy, aged
3 years 7 months, at the West Ham Hospital. He
began to squint, aged 2 years 10 months, during con-
v.ikseence from scarlet fever. Squint was at first
occasional. It became constant after a few weeks.
C. S. R. E. 42 . Good fixation K. E. Ivory ball test
shows that R. E. has at least T '\, vision. Ordered,
atropine for retinoscopy.
January 25.— C. S. R. E. 44 with atropine. Re-
tinoscopy— R. E. + 475 !) - s P h - + r 75 D - c y l ax -
70" down and in. L. E. + 475 D. Sph. + 1 D. cyl. ax.
70 down and in. Ordered, spectacles 075 n. less than
the retinoscopy : also, guttae atropine L. E. only every
morning.
February 8.— The boy uses the unatropised R. E.
always, both in near and distant vision. C. S. 32
with glasses. Ordered, stop drops.
Dining March and April exereises with the amblyo-
ILLUSTRATIVE CASES 1 5 I
scope were carried out six times. They resulted in a
fairly well-developed fusion sense with an amplitude
of fusion of about io°.
April 26. — C. S. alternating 27 .
June 7. — C. S. 21 . Fusion training.
(In a case in which I have succeeded in developing
the fusion sense, but in which there is still a consider-
able degree of deviation, the next step in the treatment
will depend upon measurements of the angle of the
deviation at each visit. If this is decreasing at a reason-
able rate, the patient is given fusion training once
every four or five weeks. This is quite sufficient to
preserve the fusion faculty, while optical treatment is
being tried. If, however, the improvement ceases, so
that nothing more is to be expected from the wearing
of glasses, operation becomes necessary.)
July 12. — C. S. 16 . Fusion training.
August 16. — C. S. 12 . Fusion training.
September 27. No squint with glasses. Good bin-
ocular vision. The mother says that the eyes became
straight soon after the last visit. He squints, some-
times when the glasses are off. When the glasses are
taken off here, in the light he does not squint ; but, in
the dark room, he turns in one or other eye most of
the time.
July 3, 1902. — The boy lost his glasses yesterday.
There is no squint in distant vision, even without the
glasses. But when he is told to pick out the letters
on a card he uses his L. E. and turns in the R. E. to
an extreme degree. He then covers the R. E. with
his hand. Ordered, repeat glasses.
Case A, 503. June 7, 1900. — A girl, 1 aged 5 months,
1 On October 23rd, 1902, a sister of this patient, an
infant aged 14 weeks, was brought to me at the West
Ham Hospital. She had C.S.L.E. about 30 . On October
30th retinoscopy under atropine + 6 d. sph. each eye. I
152 TREATMENT OF SQUINT
brought to me at the West Ham Hospital. She has
squinted constantly with the L. E. since she was twelve
weeks old. She has C. S. L. E. about 25 , variable.
Fixation lost L. E. Abversion L. E. full. Ordered,
continuous occlusion R. E., by a pad and bandage, for
fourteen days : also. ung. atropinae 1 per cent, thrice
daily, for both eyes, for retinoscopy.
June 21. — Steady central fixation L. E. Under
atropine, angle of squint varies from about 20 to 40°.
Retinoscopy R. E. + 5-5 D. sph., L. E. 4- 6-5 D. sph.
Ordered, spectacles, of the pattern described on page
102. R. E. 4- 5 D., L. E. + 6 d. Ordered also, ung.
atropinae 1 per cent., to be put into the R. E. only
every morning.
August 16. — Glasses worn well, child seems to be
quite unconscious of their presence. There is no
squint in distant vision. When looking at anything
near at hand the infant turns in the R. E. (atropiscd).
Ordered, stop the atropine.
October 8. — No deviation with glasses. When glasses
are taken off L. E. turns in to a variable degree — about
30 usually.
May 9, 1901. — No Squint with glasses.
October 3. — Glasses too small. Ordered, repeat them.
August 28, 1902. — Glasses were lost ten days ago.
The child is not squinting now, even without the
glasses. Ordered, repeat the glasses.
September 25. — No squint with glasses or without
ordered + 5^5 D. and sunt her to Mr. Hawes, of Leaden-
hall Street, who fitted spectacles of the pattern described
on page 105. When I saw her on November 6th she had
had the spectacles two days. She was wearing them quite
happily. Atropine was used for the fixing eye only until
the squint alternated. I last saw her on June 7th, 1904,
she had no deviation while wearing the glasses, and prism
test in the dark room showed that the natural development
of binocular vision was proceeding.
ILLUSTRATIVE CASES 153
them. When a lighted match was held before the
child's eyes in the dark room, she of course looked at
it. A prism, apex towards the nose, was then slipped
before one eye. This eye was immediately seen to
make a slight inward rotation (in order to blend the
images of the light), showing that the child had bin-
ocular vision.
(I do not think that hypermetropes, during the first
three or four months of life, as a rule make any pro-
longed effort of accommodation in the interests of
sharp vision. But some infants, this girl, for example,
evidently do so. The abnormal accommodative effort
caused an abnormal dynamic convergence, which was
soon succeeded by a static convergence, before the
period at which the fusion sense, normally, has made
much progress in development. By giving her a pair
of spectacles, and so relieving the strain on the accom-
modation, the visual axes were, in the course of four
or five weeks, brought back to parallelism. This
allowed the natural development of the fusion sense
to take place. The child, in spite of the high refractive
error, is perfectly cured, whether she wears glasses or
not. Nothing but an actual muscular paralysis will
ever make this child squint again.
The case of this child's sister is exactly similar.
If I had followed the practice recommended in the
text-books, of leaving the case until the child was
"old enough to wear glasses," she would then have
had an incurable squint, and almost total blindness
of the left eye.
Case B, 227. — May 16, 1900.— A girl, aged 16 years.
Her right eye is nearly blind. It turns out and down,
and is very prominent — a hideous deformity— the result
of two tenotomies six years ago.
History.— She had whooping-cough soon after she
was one year old. During convalescence the R. E.
turned in towards the nose. She was taken to an
154 TREATMENT OF SQUINT
ophthalmic surgeon at once. Being considered to be
too young for glasses, she was ordered atropine drops
for both eyes. The drops were used for both eyes, for
from a year and a half to two years. (How often one
hears this disastrous tale !) Soon after she was three
years old she was ordered spectacles. At the age of
10 years, the right eye was operated upon, in London
(tenotomy of internal rectus). A year later this eye
was again operated upon in Germany. After the
second operation the R. E. was " straight." Soon
after that it began to turn out and down. This de-
formity has gradually got worse.
At present R. E. is very prominent : it turns out
28° and down 10". With this eye she can just dis-
tinguish hand movements close to the face. Power
of adversion R. E. is absent. She is wearing spectacles
+ 175 D. sph. each eye. Vision L. E. | both with
and without glasses. Retinoscopy — with homatropine
L. E. + 2-25 D., R. E. + 3*5 D. at approximate
macula.
Of course, the blindness of the R. E. is now quite
incurable. With a view to remedying the deformity,
1 advised that the divergence should be dealt with by
operation first, and the vertical deviation at a subse-
quent operation.
May 21. — Having cocainised the eye, I stripped up
from the globe the membranes on the nasal side, from
near the edge of the cornea to the sunken caruncle.
1 found the internal rectus muscle behind the sunken
caruncle, near the inner wall of the orbit. It was not
attached to the globe in any way. As the muscle was
much wasted, I decided to advance the conjunctiva,
and capsule of Tenon also. 1 seized all these struc-
tures with forceps, and drew them between the jaws
of a Prince's advancement forceps. 1 secured these-
structures, by my usual method, to the circum-corneal
fibrous tissue, bringing the eye into a position of very
slight convergence.
ILLUSTRATIVE CASES 155
j une 16.— I advanced the right superior rectus
muscle.
j une 30.— There is still some redness of the eye.
The advancements have drawn back the eye into its
proper position in the orbit. In ordinary directions
of the gaze the eyes appear quite straight. But, when
the patient looks more than about 15 to the right,
the right eye ceases to follow the movement of the
left. This is because, owing to the wasted condition
of the internal rectus muscle, 1 did not dare to rely
upon the muscle alone, but was compelled to advance
the membranes also. But it is easy for the patient to
conceal this defect, by avoiding wide excursions of
the eyes. I ordered pince-nez + 2 D. sph.
July 5, 1902. — Patient does not wear her glasses out
of doors. She always wears them indoors. The eyes
are quite natural in appearance.
Case d, Si. September 27, 1S99 .— Boy, aged 6 years
5 months, seen at Moorfields. C. S. L. E. 27 . Ab-
version D. E. very slightly deficient. He began to
squint during convalescence from measles, aged 2\
years. He has had no treatment. Ordered, atropine
for retinoscopy.
September 30.— Retinoscopy each eye + 3 D. sph.
4- 075 D. cyl. ax. vert. Vision R. E. -£, L. E. /«.
Ordered, spectacles 0*5 D. less than the retinoscopy :
also, gutta3 atropine 1 per cent, every morning R. E.
only.
November 4. — Boy uses R. E. (atropised) in distant
vision and L. E. (unatropised) in near vision. C. S.
L. E. 1 6°. V. L. E. T V Ordered, continue drops
R. E. only.
January 3, 1900.— C. S. L. E. ii°. V. L. E. T %
partly. Boy too old for fusion training. Ordered,
continue for four months.
May 2.— C. S. L. E. 6°. V. L. E. T % partly. Or-
dered, continue drops for R. E. for two months more.
1 56 TREATMENT OF SQUINT
July 4 .-C. S. L. E. 5 . V. L. E. & partly. Or-
dered, stop drops.
February 6, 1901. — With the glasses there is no
apparent squint, but the mirror test reveals a con-
vergent squint of 2 . C. S. about 15 when the glasses
are taken off. V. R. E. f., L. E. & partly.
Case D, 734. November 29, 1901. — Girl, aged 4
years 8 months. C. S. R. E. 22 . Abversion perfect.
The power of central fixation of R. E. is lost. The
eye is so blind that, when the good eye is tied up, she
is unable to see a penny on the floor at her feet. She
hears it drop, and goes down on her knees to feel for
it. The mother says that the squint began at about
2 years of age, during an attack of scarlet fever. She
says she repeatedly spoke to the doctor about it, but
he told her to " wait to see if the child would grow out
of the squint ! " Ordered, atropine for retinoscopy.
December 3. — C. S. R. E. 26 with atropine. Retino-
scopy R. E. 4- 3 D. sph. at approximate macula. L. E.
+ 3 D. sph. Ordered, spectacles + 2*5 d. sph. each
eye : also L. E. to be continuously occluded by a
gauze pad and strapping.
January 3, 1902. — When the eye was at first tied
up, she used to fall over things, the mother says. Later,
she could see to run about very well. Child has now
central fixation R. E. Ordered, discontinue pad ;
guttae atrophia.' 1 per cent, to be put into L. E. only,
every morning. Child to go to school and use the eyes
in near vision as much as possible.
February 6. — Child uses (atropised) L. E. in distant
vision, and (unatropised) R. E. 111 near vision. Ordered,
continue atropine L. E. only.
May 2. — With glasses child uses (atropised) L. E.
in distant vision, and (unatropised) R. E. in near vision.
When the glasses air off she ums the l\. E. and turns
in L. E. always. C. S. R. E. [6° with glasses. Or-
dered, continue atropine L. E.
ILLUSTRATIVE (ASKS 157
October 3.— Vision R. E. with glasses T % easily. C. S.
R. E. 13°. Ordered, continue atropine L. E. only.
December 2. — Child uses (unatropised) R. E. now
always, both in near and distant vision, and turns in
the (atropised) L. E. C. S. L. E. 14 . Vision R. E.
I with difficulty ; f easily ; L. E. f .
(In private practice, I should have aimed at a per-
fect cure of the squint, by training the fusion sense.
But, in a crowded hospital clinic, it is, unfortunately,
not possible to find time for fusion training, except
in a very small proportion of the cases. But it is
something to have restored the sight of the blind eye.)
Case A, 541. August 9, 1900.— A boy, aged 16 years,
came to me at West Ham Hospital. He had squinted
with L. E. since infancy. He had worn glasses since
he was 4 years old. He was wearing 4- 3*5 D - s P h -
each eye. Vision with glasses, R. E. f, L. E. fo He
had C. S. L. E. n°, with his glasses. His glasses were
found to be suitable. Adversion L. E. good. Dynamic
convergence good. It was, of course, much too late
to attempt to restore the sight of the left eye. He
wished to have the deformity removed.
Under cocaine and supra-renal extract, I performed
complete central tenotomy of left internal rectus by
the method described on page 216.
August 16. — Scarcely any redness remaining. C. S.
L. E. 3 , with his glasses. This small squint is quite
masked by the angle gamma.
May 8, 1902.— Patient has, with his glasses, C. S.
L. E. 4 . There is no noticeable deformity.
Case B, 19. November 12, 1895.— A girl, aged
3 years 1 month. She began to squint during con-
valescence from measles, aged 1 year 10 months.
Squint was, at first, occasional. It soon became con-
stant. She has now C. S. alternating 36 . Ordered,
atropine for retinoscopy.
158 TREATMENT OF SQUINT
November 16. — C. S. alternating 32 , with atropine.
Ketinoscopy, each eye, + 5 D. sph. + 1 D. cyl. ax.
vert. Ordered, glasses + 4 '5 D. sph. + i D. cyl. ax.
vert.
November 27. — C. S. alternating 28 , with glasses.
Fusion training with amblyoscope.
December 5.— Fusion training. Child easily fuses
images.
December 18. — Fusion training.
January 10, 1896. — Fusion training. Child has an
amplitude of fusion of at least io°. C. S. 18 with
glasses.
January 18. — Fusion training.
February 12. — Fusion training. Child can follow the
images through a range of 15 or 20 . C. S. 12 .
March 11. — Fusion training. C. S. io°.
March 30. — No squint with glasses.
October 8. — No squint. Glasses worn comfortably.
August 21, 1897. — Child never squints now. Or-
dered, similar glasses in larger frames.
July 7, 1899. The girl never squints now, even when
the glasses are taken off ; but she must, of course,
continue to wear the glasses on account of her high
refractive error.
CASE B, II., 57. January 13, 1902. A girl, aged
1 1 years 5 months. Histoty. She began to squint
with L. E. when she was 6 years old. She has squinted
with this eye constantly ever since. When she was
about 8 years old she had glasses. In April, 1899, the
left internal rectus muscle was tenotomised, and in
June, 1899, the right also.
She now has convergent squint L. E. 15°, with the
glasses. Her vision, with her glasses, is g each eye.
She has a faint homonymous diplopia when she looks
for it. On examining her fusion sense with the am-
blyoscope she readily blends images, but has almost
no amplitude of fusion.
ILLUSTRATIVE CASES 159
January 24.— Retinoscopy under atropine, each eye,
+ 3-5 D. sph. + 1-5 D. cyl. ax. 30 down and out. This
very nearly corresponds with the glasses she has been
wearing.
February 12. —By my direction, the glasses have
been left off for the last twenty-four hours. Without
glasses, R. E. fixing, the deviation is 22 . L. E. fixing,
the deviation is 35 . (Approximate estimation by
mirror test).
I advanced the left external rectus muscle (under
cocaine), of course without tenotomising the internal
rectus. Eyes " straight " after operation.
February 19. — Removed sutures. Mirror test shows
binocular fixation.
February 28.— The patient had binocular vision,
both with and without her glasses, but the amplitude
of fusion is very small.
June 18.— Since the operation I have, by way of
experiment, attempted to increase the amplitude of
fusion, but of course without success. She has now
just the same small degree of fusion sense which she
had when she began to squint, and which she has
had ever since — neither more nor less. But an accu-
rately performed advancement has enabled her to use
this feeble fusion sense. The eyes are exactly straight
and the child has binocular vision.
The reason of the good vision in the deviating eye
is the unusually late onset of the deviation. Am-
blyopia from disuse is scarcely ever acquired after six
years of age.
Case B, 33. May 5, 1896.— Boy, aged 2 years
7 months. The right eye turned in suddenly a little
before he was two years old. He has squinted con-
stantly ever since. C. S. R. E. 27 . Central fixation
R. E. With R. E. he can with difficulty see the i| inch
ivory ball at four yards. Abversion each eye perfect.
Ordered, atropine for retinoscopy.
l6o TREATMENT OF SQUINT
May 12. — Under atropine C. S. R. E. 30". Retino-
scopy, each eye + 2*25 D. sph. Ordered, spectacles
+ 2 D. sph. constant wear : also guttae atrophia? 1 per
cent. L. E. only, every morning.
July 3. — Child uses the R. E. (unatropised) in neat-
vision and the L. E. (atropised) in distant vision. C. S.
R. E. 21 with glasses. Ordered, continue.
August 26. — Same. C. S. R. E. 18 . Ordered, con-
tinue.
October 12. — The boy uses the (unatropised) R. E.„
and turns in the (atropised) L. E., nearly always now,
even in distant vision. Ordered, continue.
November 6. — C. S. L. E. always now 12 . Ordered,
stop atropine.
November 27. — Squint alternates now o°. Fusion
training with amblyoscope.
December 4. — Fusion training. Child readily blends
images, but he has at present no amplitude of
fusion.
December 10. — Fusion training.
December 14. — Fusion training.
December 16. — Fusion training.
December 19. — Fusion training. Good amplitude of
fusion.
January 22, 1897. — No squint.
August 12. — Child wears his glasses. No squint.
October 25, 1898. — Child never squints now.
July 18, 1899 — The boy does not squint even when
tlie -lasses are taken oil.
June 13, 1902. — Ordered, atropine for retinoseopv.
June 18.— Retinoseopv R. E. + 175 I), sph. + 0*25
D. cyl., L. E. + 175 i). sph. Vision ;; each eve.
Ordered, glasses for near work + 175 D. sph. No
glasses to be worn out of sehool. To be seen again in
three months.
September 22. — The boy gets on well without glasses.
He prefers not to use them even for sehool work. He
never squints now.
ILLUSTRATIVE CASES l6l
Case B., 165. July 19, 1899.— Girl, aged 3 years
5 months. Since earliest infancy R. E. had turned
out occasionally : worse during the last year. Never
any diplopia. Always a delicate and timid child.
The eyes sometimes fix hinocularly, but more often
R. E. is widely divergent. When the child is spoken
to the eyes recover their normal relative directions
immediately, but when she looks at a near object the
R. E. is usually allowed to diverge. Dynamic con-
vergence very deficient. All separate movements of
each eye perfect. With L. E. the child easily sees
the ^ inch ivory ball at six yards. With R. E. she can
with difficulty see the 1^ inch ball at three yards.
R. E. has not lost central fixation. Amblyoscope test
shows that the child has some slight degree of fusion
sense.
July 26. — Retinoscopy under atropine, each eye +
1*25 D. sph. No glasses ordered. Ordered, guttae
atrophias sulph. 1 per cent. L. E. only every morning.
August 22. — Child now uses L. E. (atropised) for
distance, and R. E. (unatropised) in near vision.
Ordered, continue.
October 27. — Child uses R. E. in near vision and
sometimes in distant vision also. W T ith R. E. she can
easily see the f inch ivory ball at six yards. Ordered,
atropine L. E. only every morning, first seven days in
each month, for six months.
September 20, 1900. — Divergence is nearly alternating.
Still some preference for fixing with L. E.
July 16, 1902. — Divergence almost always present
now. V. R. E. -I partly, V. L. E. f.
July 29. — Advancement R. internal rectus muscle,
under cocaine. Patient kept in bed with both eyes
bandaged for one week after. Stitches then removed.
Two days later all dressings discontinued.
August 26. — Eyes "straight." Child blends images
except on looking to extreme R.
(The feeble degree of fusion sense which developed
1 62 TREATMENT OF SQUINT
in early childhood was nut sufficient to prevent the
deviation, or even to cause diplopia, but now that the
deviation has been overcome by operation it enables
her to fuse the two images.)
Case B, 166. July 19, 1899. — Girl, aged 8 years 2
months, sister of the preceding case. Alternating
divergent squint of variable degree, usually about 35 .
Association between accommodation and convergence
almost absent. Separate movements each eye normal,
except adversion, which is slightly deficient. Fusion
sense absent. H.m. 0-5 D. No As. V. each eye f.
Child has worn spectacles + 075 D. sph. for about
three years. Recommended advancement of one or
both internal recti for cosmetic reasons. No glasses
required.
August 22. — Advancement R. internal rectus, under
cocaine (of course without tenotomy of externus.)
November 8. — Advancement L. internal rectus.
December 20. — No noticeable deformity now. Eyes
appear to be quite normally directed. Mirror test,
however, shows that there is sometimes slight diverg-
ence and sometimes slight convergence. Of course
there is no fusion : she really uses the eyes alternately,
although she appears to use them together.
October 5, 1904. — Condition as at last visit five years
ago.
Casio A, 79. December 5, [895. Girl, aged 16 years.
Eyes are already under atropine. L. E. is widely
divergent. When told to look at a near object she can,
by an effort, overcome the deviation, but the eye soon
diverges again. Adversion slightly deficient. Patient is
known to have been "short-sighted for some years;
getting worse." Four or five years ago L. E. turned
out, occasionally at first, but during the last year
constantly. She often sees double. Small myopic
crescent each eve. Choroidal vessels seen. Retino-
ILLUSTRATIVE CASES I 63
scopy R. E. — 6-5 I), spli. V. | partly. L. E. -
6*5 D. sph. — 175 D. cyl. ax. 15 down and out.
V. f. Ordered, full correction to be worn con-
stantly.
February 13, 1896. — When she Hrst began to wear
the glasses they made her head ache, but she soon
became accustomed to them. Now she finds them
quite comfortable. No divergence now. When she
is tired she " squints and sees double for a moment
until the eyes come straight again." While wearing
the glasses either eye diverges when screened, about
20 .
October 8. — Glasses very comfortable. No headaches.
No divergence. Behind Maddox rod either eye turns
out 12 , varies slightly.
September 23, 1897. — Retinoscopy under atropine
shows that the myopia has increased 075 D. Ordered,
continue same glasses.
July 20, 1899. She is never seen to squint, but
says that she occasionally sees double for a moment.
Behind Maddox rod either eye diverges 8° or 9 .
July 27. Retinoscopy under atropine. R. E. —
7-5 D. sph. V. § L. E. - 75 D. sph. - 175 D. cyl.
ax. 12 down and out. V. f. Ordered, full correction,
to be worn constantly.
August 20, 1903. — Eyes comfortable. Never any
divergence. Exophoria is now only 2 .
August 27. — Retinoscopy under atropine shows that
the myopia has increased less than 0-5 D. during the
last four years.
,6 4
CHAPTER XI
HETEROPHORIA.
If a person, with a perfectly normal pair of
eyes, looks steadily at any object, both visual
axes will continue to be accurately directed to
that object, even though one eye be shaded. 1 n
other words, his perfectly balanced motor coordi-
nations are able to maintain the normal relative
directions of the eyes, even when the controlling
influence of the fusion sense is temporarily with-
drawn. This state of perfect oculo-motor equi-
librium is called orthophoria.
Heterophoria is the name given to the con-
dition of imperfect oculo-motor balance. There
is here a tendency for the eyes to deviate from
their normal relative directions. Ordinarily, how-
ever, this tendency is kept in check by the fusion
sense, so that there is no squint. But if binocular
vision be temporarily rendered impossible — e.g.,
by covering one eye — this tendency gives rise to
an actual deviation.
Heterophoria of sufficient degree to cause
trouble is not very common. Of those who suffer
from "asthenopic symptoms," in only a very
small proportion of cases are the symptoms found
HETEROPHORIA. 1 65
to be due to heterophoria. Occasionally, how-
ever, one meets with a patient who complains of
pain and discomfort in the eyes, and whose refrac-
tion has been repeatedly examined, and who has
for years worn glasses to correct some unim-
portant refractive error, without any relief to his
suffering. Such a patient usually has a hetero-
phoria, the correction of which immediately and
permanently removes his trouble.
Heterophoria may perhaps be due to a muscle
or group of muscles being too weak or too strong
for the opponents, or to an abnormal position of
insertion of a tendon, whereby the muscle acts at
less or more than its normal mechanical advan-
tage, or to a muscle or group of muscles being
too feebly, or too powerfully, innervated. As a
rule, we are unable to determine whether the fault
lies in the muscles themselves, or in their innerva-
tions. We can only say that certain actions are
deficient or excessive. Heterophoria is essen-
tially a motor anomaly.
Squint, on the other hand, is essentially due
to a defect of the fusion faculty. In the presence
of this fundamental cjiuse, heterophoria may give
rise to a permanent squint with suppression of one
image : not otherwise.
There is an apparent exception to this rule — a
person who has previously enjoyed perfect bino-
cular vision may have the visual acuity of one
eye so lowered by progressive myopia, injury, or
12
I 66 HETEROPIIORIA
disease as to render binocular vision impossible.
Any heterophoria which may be present will then
cause a manifest squint, although the cerebral
faculty of fusion remains perfect.
Heterophoria is the generic name, invented by
Stevens, for all latent tendencies to deviation.
Distinctive names are employed to indicate the
direction of the tendency : —
Esophoria is a tendency to abnormal static
convergence of the visual axes.
Exophoria is a tendency to divergence of the
visual axes.
Hyperphoria is a tendency of the two eyes to
rotate vertically in opposite directions, so that
one visual axis shall lie in a higher plane than
the other. The eye which tends to turn upwards
is called the hyperphoric eye.
Cyclophoria is a tendency to abnormal rotation
of one or both eyes round a fore-and-aft axis, so
that what should be the vertical meridian of the
eye shall be no longer parallel to the median
plane of the head. A tendency for the vertical
meridian of the eye to lean away from the median
plane is called plus cyclophoria. A tendency in
the opposite direction is called minus cyclophoria.
Pseudo-heterophoria. — In a case of uncorrected
ametropia there is frequently an apparent hetero-
phoria which disappears when the appropriate
correcting glasses are worn. The term hetero-
phoria should be reserved for cases in which the
HETEROPHORIA \6j
anomaly persists after optical correction of any
refractive error which may be present.
If the patient be ametropic, he should wear an
exact correction of his ametropia during the ex-
amination. But this spurious heterophoria does
not always disappear immediately on correcting
the refractive error. So that, if the latter be con-
siderable, one should not immediately conclude
that any heterophoria which may be found is
genuine. The results should be checked by a
second examination after glasses correcting the
refractive error have been worn for several weeks.
The symptoms of heterophoria are those of
" eye-strain " in general — frontal headache coming
on towards the end of the day ; pain in the eyes
after watching anything intently, e.g., a play ; mi-
graine ; dizziness (especially associated with hy-
perphoria) ; conjunctival hyperemia, &c. In the
higher degrees of heterophoria momentary de-
viation with diplopia is not uncommon.
Asthenopic symptoms, which do not yield to
accurate optical correction of any refractive error
which may be present, should always lead to
investigation of the motor balance of the eyes, if
this has not already taken place.
People vary greatly in their susceptibility to
suffering as the result of heterophoria, just as
they do in the case of refractive error. Other
things being equal, hyperphoria is the form of
heterophoria which is most likely to cause trouble,
l68 HETEROPHORIA
and esophoria the least. It is not uncommon to
see a patient who has several degrees of eso-
phoria, and who is quite unconscious of any defect ;
whereas few men can support a hyperphoria of
more than one degree without inconvenience.
The importance of a case of heterophoria is
proportionate to the trouble which it causes. A
case which gives rise to no symptoms requires no
treatment.
Heterotropia. — A person whose fusion sense
has developed perfectly, but who has a very high
degree of heterophoria, will be able (with more
or less suffering) to keep this deviation-tendency
in check during the adaptable and vigorous
period of childhood and youth, but, when he
exchanges school life for some more trying and
less healthy occupation, he may find himself
unable to continue the struggle, in which event
his heterophoria gives rise to an actual deviation.
He then loses his asthenopic symptoms, but he
suffers from diplopia, which is usually so annoy-
ing that he is glad to shade or close one eye.
The degree of the manifest deviation increases
during the first few weeks or months, after which
it becomes stationary. The term heterotropia
should be reserved for this rather rare condition,
as it is obviously a further stage of heterophoria,
and not a true squint nor a paralysis. The case
of Mr. S. H., page 195, is a typical example.
Hi e methods 0/ testing the muscular balance
HETEROPHORIA
169
of the eyes. — In a case of heterophoria, under
ordinary circumstances, the desire for binocular
vision prevents the eyes from deviating from
their normal relative directions. But if, by
artificial means, the image formed in one eye
be so altered in appearance or position as to
make fusion with the other unaltered image im-
possible, the control of the fusion-sense is sus-
pended. The heterophoria then gives rise to a
manifest deviation. The altered image in the
deviating eye is not suppressed as in a case of
squint. The diplopia, therefore, gives an easy
means of ascertaining the direction and degree
of the deviation. This is the principle on which
all subjective tests for heterophoria are based.
The instruments required for the tests which
I am about to describe are the Maddox rod and
tangent scale, the Maddox double prism, an
adjustable trial frame, test cards, and a set of
prisms whose axes are accurately marked. A
rotary prism also is very useful.
I JO HETEROPHORIA
The Maddox rod (fig. 1 9). A transparent round
glass rod is, in effect, a very strong cylindrical lens.
Rays of light, therefore, which pass through it
are dispersed in one plane only, at right angles to
the axis of the rod. So that if a point of light be
looked at through this rod, it will appear as a long-
narrow band of light. For the sake of convenience,
half a dozen of these pieces of glass rod are fixed,
side by side, in a metal disc of such a size as to
fit into an ordinary trial frame. The rods are
generally made of red glass, to increase the con-
trast between this band of light and the true
image. An equally good plan is to have the
rods made of colourless glass and to put a plane
red glass before the other eye.
In looking at a flame, with the rod before one
eye and the other eye naked, the naked eye will of
course see the flame and the surrounding objects ;
but, to the rod-clad eye, the flame will appear as
a long streak of light, and less luminous objects
will not be visible at all. It is not possible to
blend two such dissimilar images as the Maine and
the streak, 1 so the function of fusion is temporarily
1 The images should be differently coloured. The rods
should be carefully fitted side by side, so that it is not
possible to see between them. The source of light at the
zero of the scale should, if possible, be a frosted incan-
descent electric lamp. Failing this, any bright flame,
enclosed in a tin chimney having a hole of about i£ inch
diameter in one side of it, will serve the purpose. The
room should not be too brightly illuminated. As the rods
HETEROPHORIA
171
suspended, and the eyes are merely controlled by
their motor coordinations. If there be no motor
anomaly, the streak, seen by the rod-clad eye,
will appear to pass through the flame, seen by the
< . -
\
3
J
l a 1 1 2 2
9-8-7-6-J-V3*i'1-i-l-a'3«V-l*6-7-8-SI-'o
Fig. 20
naked eye. But if there be any heterophoria it
will now be able to cause the eyes to deviate, the
relative positions of the streak and light indicating
the direction and degree of the deviation.
produce extreme distortion in one direction only, a well
marked vertical line can be seen through the rods when
their axes are horizontal, and a horizontal line can be seen
when their axes are vertical. Care should therefore be
taken that there be no prominent horizontal or vertical lines
near the centre of the field of vision. F'or this reason, the
paper on which the tangent scale is printed should be of
nearly the same colour as the background on which it is
hung : or the large figures may be marked on the wall
itself. With these precautions, I have always found the
rod test quite reliable.
172 HETEROPHORIA
The tangent scale is shown in fig. 20. The
large figures on the horizontal and vertical scales
denote tangents to degrees at a distance of 5
metres. A small electric or other light is placed
at the zero of the scale.
Fig. 21.
The Maddox double prism (fig. 21) consists of
two prisms, each of 4 , 1 cemented base to base.
When this double prism is placed with its apices
vertical, before one eye, so that the line of junc-
tion of the bases crosses the pupil horizontally,
1 To avoid confusion, the strength of a prism is always,
in this book, denoted by the number of degrees which it
deflects a ray of light. Chromatic dispersion produces 110
appreciable error in the weak prisms used in ophthalmology.
An optician usually numbers a prism according to the
widtli of its geometrical angle (the angle between the two
plane surfaces). The refracting power of such a prism
varies according to the kind of glass of which it is made.
For practical purposes it may be taken as half the geo-
metrical angle. For instance, a prism which deflects .1 raj
of light to the extent of 4 will have a geometrical angle
of about 8°.
HETEROPHORIA I J$
two false images of any small object will be seen,
one above and the other below its true position.
If now the other (naked) eye be opened, it will
see the real image of the object mid-way between
the two false images. The false images are not
changed in appearance, but the vertical displace-
ment of each is too great to admit of the true
imaoe beino- blended with either of them. The
eyes are thus temporarily deprived of the control
of the fusion sense and abandoned to their motor
coordinations, just as in the last test.
In looking at a horizontal line, the true image
can of course not be made to approach either of
the two false images ; but care must be taken that
there be no long vertical line near the centre of
the field of vision.
The test cards which I use consist of two pieces
of strong white cardboard each 2 feet square.
Number I. card has in its centre a straight black
line 2 inches long. In the centre of Number II.
card are ten letters of " Pearl " type having a
large capital O in the middle. The cards are
meant for use at the reading distance. The
reason for making them so large is that the
objects shall be seen in the centre of a blank
field with no edges near to solicit fusion.
In the examination I begin with the Maddox
rod. The patient is seated before the tangent
scale, at a distance of 5 metres from it. If he be
not absolutely emmetropic, he wears correcting
1/4 IIKTEROPHORIA
Number I. test card.
Fig. 22.
Nu in lu-r II. test card.
Fig. 23.
HETEROPHORIA 1 75
lenses in the trial frame in every test. The frame
is adjusted so that the lenses are accurately centred
for distant vision. The rod, with its axis horizon-
tal, is put in the frame before the right eye. The
light, at the zero of the tangent scale, is switched
on. If the vertical streak, seen by the right eye,
appears to go through the light, seen by the left
eye, the patient has no esophoria or exophoria in
distant vision. Now rotate the rod so that its
Fig. 24. 1
axis is vertical. If the horizontal streak, now seen
by the right eye, appears to pass through the light
seen by the left eye, the patient has no hyper-
phoria in distant vision.
Now remove the rod and replace it with the
double prism, with apices vertical (line of junction
of bases horizontal). Adjust the trial frame for
near vision. Let the patient hold in his hand
Number I. test card, with the line horizontal.
1 This and the two succeeding figures are taken from
a paper on " Insufficiency of the Obliques," by Dr. Savage,
of Nashville, U.S.A., "Archives of Ophthalmology," Janu-
ary, 1S91. "Ophthalmic Myology," by the same author,
contains the fullest account of cyclophoria which has
hitherto been published.
1 j6 IIETEROPHORIA
He will see two false images of the horizontal
line with the prism-clad eye, and between them,
he will see the true image with the naked eye.
If the middle line appears equidistant from each
of the other lines, and has its ends level with their
ends (fig. 24) there is no hyperphoria, esophoria,
or exophoria in near vision. If the middle line
appears parallel to the other two lines, as in
this figure, there is no cyclophoria. The patient's
oculo -motor equilibrium, therefore, is perfect in
every respect.
If, however, any anomaly be found during these
proceedings, further examinations will be required.
In the distant vision test with the Maddox rod,
axis horizontal, before the right eye, if the vertical
streak lies to the right of the light (homonymous
diplopia), there is esophoria. If it lies to the
left of the light (crossed diplopia), there is exo-
phoria. The figure on the tangent scale, through
which the vertical streak passes, numerates the
degree of the defect. As a control test, change
the rod from the right eye to the left. The posi-
tion of the streak also changes over, that is, it
still shows the same kind of diplopia. The
degree of heterophoria indicated is the same as
before. Now place before one eye a prism of
the same degree as the defect, base out in eso-
phoria, base in in exophoria. This should cause
the streak to pass through the light.
In using the rod, axis vertical, before the right
HETEROPHORIA \JJ
eye, if the horizontal streak is seen below the light,
this indicates that the right eye tends to turn
upwards relatively to the left eye (right hyper-
phoria). If the streak is seen above the light,
the left eye tends to turn upwards relatively to
the right eye (left hyperphoria). The figure, on
the vertical scale, which the streak appears to
cross, numerates the degree of the hyperphoria.
Now change the rod from the right to the left
eye. Almost invariably, if the right eye saw the
streak above the light, the left eye will now see it
below, and vice versa. That is to say, the hyper-
phoria is comitant. The result should be checked
by neutralising the hyperphoria with a prism of
the strength indicated by the position of the
streak.
In rather rare instances it happens that each
eye, in turn, rotates upwards behind the rod
(double hyperphoria).
In the near vision test with the double prism
before the right eye, and the Number I. test card,
the middle line, seen by the left eye, should be
equidistant between the two false images, seen by
the right eye. If it lies nearer the upper false
image, there is right hyperphoria. If it lies
nearer the lower false image, there is left hyper-
phoria. The prism, base down, before the hyper-
phoria eye, which places the line half-way between
the two false images, will serve to measure the
degree of the anomalv.
i ;8
IIKTEROPHORIA
If the three lines are not all level with each
other at the ends, hand the patient Number II.
test card and tell him to read the letters on it.
The small letters are to ensure a normal effort
of accommodation. If presbyopic, the patient is
allowed glasses. He will see the true image of
the object between its two false images. In ortho-
phoria the three images will be in the same
vertical line. If the middle image, seen by the
left eye, is to the left of the two false images, the
patient has esophoria in near vision. If it is to
the right, he has exophoria in near vision. The
prism, axis horizontal, which will bring the three
O's in line, is a measure of the defect. In near
vision it is better to measure with prisms than to
use any kind of small tangent scale, because with
the former the distance from the eye is of no
consequence, whereas with the latter the smallest
HETEROPHORIA 179
variation introduces an error. The study of eso-
phoria and exophoria in near vision is intimately
associated with that of convergence anomalies.
When the patient looks at the horizontal line
on Number I. card, with both eyes open and the
double prism before the right eye, the three lines
should be parallel (fig. 24). If not, there is cyclo-
phoria. Suppose the middle line, seen by the
left eye, seems to dip down to the left as in fig. 25,
this shows that the vertical meridians of the eyes
are leaning in the opposite direction, towards each
other (minus cyclophoria). If the middle line,
seen by the left eye, appears to dip down to the
right as in fig 26, there is plus cyclophoria.
Prism duction should always be investigated in
any case in which heterophoria has been found.
Seat the patient at a distance of five or six
metres from a candle flame. Let him wear a trial
frame. While he looks steadily at the light, put
a i° prism, apex up, before the right eye. Grad-
ually increase the strength of the prism, until the
highest prism is found which the patient can bear
without seeing double. This indicates the extreme
range of superduction of the right eye. Now test
the superduction of the left eye. The subduction
of each eye is similarly tested, with prisms apex
down. The power of binocular abduction is
tested with prisms apex out. Binocular adduction
is so intimately associated with accommodation
that an attempt to measure it with prisms (which
I So HETEROPHORIA
cause the eyes to converge without accommo-
dating) gives very variable and misleading results.
The normal limits of prism duction are as
follows : — -
Superduction ... ... i^-° to i\°
Subduction i|° to 2J-
Abduction ... ... 4 to 5
No amount of practice appears to increase the
duction power in these three directions. Con-
vergence, on the other hand, can nearly always
Fig. 27.
be much increased by practice. As the degree
of prism-duction does not vary from time to time,
and is independent of voluntary effort on the part
of the patient, the information obtained is reliable.
A rotary prism, (fig. 27) is very convenient for
measuring duction. It consists of two prisms of
equal strength, mounted in a metal disc in such a
position that the apex of each coincides with the
base of the other. In this position they, of course,
neutralise each other. By a mechanical arrange-
HETEROPHORIA
181
ment, the two prisms can be rotated in opposite
directions at equal rates. The strength of the
compound prism can be thus gradually increased
from zero up to the combined strength of the two
components.
Fig. zi
Phorometer. — Fig. 28 shows an instrument which I
have found very useful for measuring heterophoria. A
rod-shaped wooden box 24 inches by 2 inches by 2 inches,
is supported on a stand by a horizontal bolt, so that it
is free to rotate in a vertical plane. (A two-foot length
13
1 82 HETEROPHORIA
of brass optical tube would do as well as the rod-
shaped box). In the face of this rod-shaped box are
three openings, each 3 inches by -§ inch. In the centre
opening is fitted a piece of frosted red glass. 1 In each
of the two other openings is a piece of frosted green
glass. In the box, behind each glass, is a small electric
lamp having a tin reflector behind it to increase the
illumination. The box is ventilated by holes in the
back. On the back of the stand is a brass protractor,
marked in degrees, to show the axis at which the rod-
shaped box is placed.
The room is partially darkened by drawing down
the blinds. The patient is seated in front of the
instrument at a distance of about 8 or 10 feet. In a
trial-frame he wears a red glass before the right eye,
and a green glass before the left. With the right eye
he sees nothing but the centre red light ; and with the
left eye he sees nothing but the two green lights.
The angular distance between the lights is sufficiently great
to avoid any tendency to fuse the red light with cither of
the green lights, so that the eyes are perfectly dissociated.
First the rod-shaped box is put horizontal and the
patient is asked whether the three lights appear in the
same straight line. If they do, he has no hyperphoria.
If the red appears below the level of the green lights,
he has right hyperphoria. If it appears above, he has
left hyperphoria. The degree of the defect is measured
by putting a rotary prism (fig. 27) in the trial-frame
and screwing it up until the lights appear in line.
Esophoria and exophoria are similarly detected and
measured by placing the rod-shaped box vertical — red
to the right indicating esophoria, and red to the left,
exophoria.
1 I believe that Mr. Lang was the first to use Snellen's
coloured glasses for the measurement of heterophoria. His
apparatus is described in " The Methodical Examination
of the Eye," page 52.
HETEROPHORIA I»3
If one wishes to ascertain the direction of a com-
pound defect, such, for instance, as esophoria with
right hyperphoria, the box is rotated until the lights
are in the same straight line, though of course not
equidistant from each other. The axis is then read off
from the protractor at the back of the stand. To
ascertain the degree of the compound defect, place the
box with its axis at right angles to this, then screw up
the rotary prism until the lights are again in the same
straight line.
Esophoria.
The liability of an esophoria to cause trouble is
determined not so much by its degree as by the
condition of the functions of abversion and binocu
lar abduction. A patient who can abvert each
eye separately until the cornea touches the outer
canthus, and whose binocular abduction is not
less than 3 , will as a rule be able to support
many degrees of esophoria without inconvenience.
In many cases of esophoria of high degree
there is occasional momentary diplopia. When
the patient is gazing vacantly without perceiving
what is before his eyes, perhaps the visual axes
may deviate. Instantly the diplopia awakens the
dormant fusion sense, and the eyes immediately
recover themselves. These cases are often mis-
taken for occasional convergent squint. Occa-
sional squints, however, differ from esophoria in
that the fusion sense is defective, so that the
deviation is not so instantly corrected, and diplopia
is either absent or very faint. In an occasional
184 HETEROPHORIA
squint, too, examination with the Maddox rod
shows that when the deviation is not actually
present there is little or no tendency to con-
vergence. In a case of occasional squint, we
have a pair of eyes, not properly controlled by
the fusion sense, responding- to intermittent and
varying nervous impulses. In esophoria there is
a constant and definite motor anomaly which is
kept in check by a perfect fusion faculty.
Treatment. — Moderate degrees of esophoria
never cause inconvenience unless the binocular
abduction is very deficient. In these cases the
symptoms are relieved by the constant wearing
of prisms, apex in, which represent the deficiency
of binocular abduction [not the degree of eso-
phoria). The prism should be divided between
the two eyes. For example, a patient with 5 of
esophoria will probably not be inconvenienced
thereby. But if his binocular abduction is only
2 instead of 4 he is likely to suffer from " asthe-
nopic " symptoms and occasional diplopia. He
will be relieved by wearing prisms, apex in,
having a total deviating power of 2 . If the
patient already wears glasses for correction of a
focal error, the prismatic effect may perhaps be
got by decentration of lenses (see Appendix).
In a case of esophoria of high degree requiring
treatment, operation is the only resort. If the
esophoria is not less then 7 in distant vision,
and the near vision test shows the same or a
HETEROPHORIA 185
higher degree, and if abversion and binocular
abduction are not markedly below normal, the
best procedure is complete central tenotomy of
an internal rectus, by the method described on
p. 216. If the degree of esophoria is less in
near vision than in distant vision, tenotomy is
contra-indicated. In a case of esophoria of high
degree, with abduction less than 2°, and abver-
sion subnormal, and frequent momentary diplopia,
advancement of an external rectus should be
performed.
Exophoria.
Uncomplicated exophoria of moderate degree
seldom causes any inconvenience. But if, as
occasionally happens, there is a defect of dynamic
convergence in addition, the patient is likely to
suffer from frontal headache, not only after using
the eyes in near vision, but often at other times
also. In cases of exophoria of high degree the
eyes may momentarily deviate, but this is less
common than in esophoria.
Treatment. — Prisms are seldom of use in exo-
phoria. Slight cases require no treatment, if
uncomplicated. If the case be complicated by
convergence deficiency, treatment should be
directed to this anomaly. Even if there be no
deficiency of dynamic convergence, convergence
training often relieves the patient's symptoms,
but, in my experience, the effect has been only
jS6 heterophoria
transitory. In higher degrees of exophoria, espe-
cially if adversion be deficient, the internal rectus
muscle should be advanced. One should then
aim at producing an operative effect exactly equal
to the degree of the exophoria of distant vision,
Exophoria is almost invariably due to under-
action of the internal recti, scarcely ever to over-
action of the externi. For this reason, tenotomy
of the rectus externus is not advisable.
Hyperphoria.
Clinically, hyperphoria is the most important of
all forms of heterophoria, because of the severity
of the symptoms to which it is liable to give rise,
and the certainty with which these symptoms may
be relieved. The liability of a case to cause
trouble depends not only upon the degree of the
hyperphoria, but upon the extent of any deficiency
of prism-duction in the opposite direction. For
instance, an ordinary healthy man who has |° of
rio-ht hyperphoria will probably suffer no incon-
venience if the right subduction is as much as 2°:
but if it is only i° or less, he is almost certain to
have trouble.
The commonest symptom is frontal headache,
coming on towards the end of the day, not espe-
cially caused by near work. Some patients com-
plain of giddiness on looking down. Momentary
diplopia is not uncommon.
In a marked case of hyperphoria, more often
HETEROPHORIA 1 87
than not, the palpebral fissure on the hyper-
phoria side is smaller than that on the other.
This asymmetry disappears entirely when the
hyperphoria is corrected.
The treatment, in any case of hyperphoria of
moderate degree, is by prisms to be worn con-
stantly. The prism should be placed, apex up,
before the hyperphoric eye. Or, if more than i°
is required, the effect may be divided between the
two eyes, the prism before the other eye being
placed, of course, apex down. The strength of
the prisms should be determined partly by the
degree of the hyperphoria and partly by the
range of prism duction (see page 179). One
should attempt as nearly as possible to correct
the hyperphoria and to bring each eye into the
middle of the vertical range of prism duction.
For example, take a case of right hyperphoria 2 ,
in which the right superduction (and left subduc-
tion) is 3 and the right subduction (and left
superduction) is i°. A prism, apex up, before
the right eye, 2 would correct the hyperphoria :
but a prism of i° would suffice to bring the eye
into the middle of the range of prism duction.
In this case one would order a prism of il- as a
compromise.
If the hyperphoria is very high — over 4 —
operation is usually indicated. If subduction of
the hyperphoric eye is not less than i°, and super-
duction over 4 , complete central tenotomy of the
1 88 HETEROPHORIA
superior rectus of this eye is the best procedure.
In a case of hyperphoria of very high degree,
with very deficient subduction, the inferior
rectus muscle of the hyperphoric eye should be
advanced.
I have seen a few well-marked cases of so-called
double hyperphoria. In all there was more or less
drooping of both eyelids. A great effort was
required to open the eyes widely while looking
straight ahead, but in looking up, the lids were
lifted normally. Either eye turned up when
screened. Subduction of either eye was normal.
These cases were possibly due to a faulty nervous
connection between the superior recti muscles and
the levatores palpebral superiores. In two of these
cases I performed complete central tenotomy of
both superior recti, with excellent results.
I have seen several cases of double hyper-
phoria associated with plus cyclophoria — due
probably to underaction of the superior oblique
muscles.
I have no note of any case of double kata-
phoria (downward tendency of each eye).
Cyc/ophoria.
In order that binocular vision may be possible
it is necessary not only that the visual axes of the
two eyes shall be directed to the same object, but
that their vertical diameters shall be parallel.
The work of keeping the vertical diameters
HETEROPHORIA 1 89
parallel falls almost entirely upon the oblique
muscles. If the superior obliques act too feebly,
the eyes tend to rotate round a fore-and-aft axis
so that their vertical diameters diverge above
(plus cyclophoria.) This is very much more
common than minus cyclophoria. Plus cyclo-
phoria is not infrequently associated with double
hyperphoria.
Cyclophoria may cause nausea, vertigo, and
difficulty in judging the true position of the steps
in going downstairs.
Not much can be done in the way of direct
treatment in cases of cyclophoria. But there
are some practical points which deserve careful
study.
Close one eye, and hold before the other a
strong convex cylindrical lens, axis vertical. Look
at a horizontal line, the junction of a floor and
ceiling, for instance. The horizontal line still
appears horizontal. Now rotate the lens a few
degrees. The horizontal line appears to rotate
slightly with the lens. In other words, the cylin-
drical lens rotates the image of the line towards
its meridian of greatest convexity.
Next put on a trial-frame and place before
each eye a + i d. cylindrical lens, axis vertical.
Vision will be slightly blurred, but objects will not
appear displaced, and the lenses can be worn for
a long time without discomfort. Now rotate each
lens about 30 , so that their axes diverge above.
190
HETEROPHORIA
On looking down, the floor seems far away, and,
on looking up, the ceiling seems quite near — one
feels about 7 feet high. Now rotate the cylinders
in the opposite direction, so that their axes con-
verge above. The floor appears quite near, and
the ceiling high — one feels a dwarf. After a few
minutes of this artificial oblique astigmatism, one
experiences a feeling of giddiness and nausea,
reminiscent of the "giant stride" in one's early
school days.
In the light of the former experiment, the
explanation is plain. We are accustomed to
localise all objects with reference to the horizontal
surface (floor, ground, or sea) which supports us.
While wearing the convex cylinders with axes
divergent above, the images of the horizontal
surface of the floor are tilted outwards towards
each temple. In order that these images may be
received upon corresponding points of the two
retinae, each eye must rotate about a fore-and-aft
axis so that the vertical diameters diverge above.
This is accomplished by a lessened action of the
superior oblique muscles and an increased action
of the inferior obliques. But this has also the
effect of rotating the two eyes a little upwards.
So that, in looking down to the floor, one has to
put forth sufficient energy to overcome this up-
ward tendency, as well as to effect the actual
downward rotation. And in looking at the
ceiling, less than the normal expenditure of energy
HETEROPHORIA I 9 I
is required, owing to the eyes already having an
upward tendency. We depend chiefiy upon the
" muscular sense " of the external ocular muscles
in judging the relative positions of objects.
Therefore, the increased effort required in look-
ing down, makes the floor appear farther away,
and the lessened effort in looking up, makes the
ceiling appear lower.
In the experiment with the axes of the cylinders
convergent above, the conditions are exactly
reversed.
This experiment appears to explain the com-
monly observed fact that astigmatism is more
liable to cause trouble when the axes are oblique
than when they are vertical or horizontal. Un-
corrected astigmatism, unless the axes in the two
eyes are parallel or at right angles, must cause a
pseudo-cyclophoria, which should disappear when
the astigmatism is corrected.
Now and then one meets with a patient, with
oblique astigmatism who is less comfortable with
glasses which accurately correct his refractive
error than he was without any correction at all.
In such a case, one generally finds that he has
cyclophoria of an opposite kind to the pseudo-
cyclophoria which would be produced by his un-
corrected astigmatism. So that they, to a certain
extent, neutralised each other. But, with the
correction of his astigmatism, the whole of his
true cyclophoria becomes manifest. A slight
192
HKTEROPIIORIA
rotation, say about 5 , of both his cylinders, in the
direction which favours the feebly-acting pair of
oblique muscles, will often make him quite com-
fortable without appreciably lowering his visual
acuity.
Under certain conditions it is possible, without any
rotation of the eyes round a fore and aft axis, to blend
images of lines whicli are slightly tilted in opposite
directions (see page 11). Some authors have therefore
assumed that the eyes never make an axial rotation in
the interests of binocular vision. This view does not
accord with clinical and experimental evidence. Fu-
sion of tilted images takes place according to the law
stated on page 1 1 .
Rhythmic exercises with prisms, cylinders, &c,
are employed by many eminent ophthalmologists
in America. 1 have thoroughly tried all the most
approved methods, but have never been able
to satisfy myself that I have produced any effect
in any case of esophoria or hyperphoria. Cases
of exophoria are indirectly benefited by exer-
cising the dynamic convergence, but that is a
different matter.
In America there is, no doubt, a tendency to
overestimate the importance of small latent devia-
tion tendencies. But this is less harmful than
the almost total neglect which the subject meets
with in this country.
Here are some examples : —
Mr. R. H. t aged 38, a hard worker, and head of <i
large city business, consulted me on October 17, 1899.
HETEROPHORIA
93
He complained of dull, aching pains in the eyes and
forehead. Pain was always relieved by sleep. It was
not especially associated with near work. He suffered
almost as much during his holidays. His eyes had
been examined many times, and he had worn glasses
for twelve years. There was a slight drooping of the
left upper lid. He was wearing + 2-25 D. sph. each
eye. He showed me several prescriptions for glasses,
all practically the same. Retinoscopy without my-
driatic showed 2 D. of hypermetropia each eye, no
astigmatism. His corrected vision was £ easily, each
eye. On investigating the motor balance of his eyes,
I found he had nearly 2 left hyperphoria. Left
superduction and right subduction were each 4 ; and
left subduction and right superduction were each i°.
I ordered spectacles + 2 D. sph. each eye, the right
lens to be combined with a f° prism, apex down, and
the left lens with a similar prism, apex up.
On September 26, 1902, three years later, I saw the
patient again. He has worn the glasses constantly,
with perfect comfort, and is entirely free from the old
trouble.
Miss E. B., aged 33, seen with Mr. Devereux Mar-
shall on February 6, 1903. Patient had suffered from
frontal headache and occasional diplopia for as long as
she could remember. Headaches were always relieved
by sleep, were independent of occupation, and became
more severe towards the end of the day. She had for
many years worn an exact correction of her ametropia
(4- 075 D. cyl. ax. vert, each eye), but the glasses gave
her no relief.
On investigating the motor balance of the eyes we
found left hyperphoria 4 , exophoria i°. Right super-
duction and left subduction barely i°. Right sub-
duction and left superduction each 6°. We ordered, for
constant wear, to be incorporated with her cylinders,
R. E. prisms i^-°, apex down, L. E. prism i^°, apex up.
194
HETEROPHORIA
The patient has been seen twice since that date.
She is perfectly comfortable and entirely free from
headaches.
Miss F. L., aged 17, was brought to me on February 2,
1900. She was wearing spectacles + 1 D. sph. She
said that when she was tired her eyes would often be
crossed for a moment and she then would see double.
The crossing of the eyes only lasted an instant. She
had frequent frontal headaches. She had worn glasses
since she was ten years of age. She had been told that
she suffered from " periodic strabismus." Retinoscopy
without mydriatic showed hypermetropia of 0-5 D.
only. Vision of each eye f. Examination with the
Maddox rod and tangent scale showed esophoria, 9 ,
in distant vision. Esophoria, in near vision, was 8°.
Binocular prism abduction was only 2 . R. E. could
be abverted until the cornea touched the outer canthus.
L. E. abversion not quite so complete. The fusion
faculty was perfect. The case was not one of " periodic
strabismus" at all, but an example of esophoria of
high degree.
February 5, 1900. — Retinoscopy was confirmed under
atropine.
February 20, 1900. — I advanced the left external
rectus muscle (of course without tenotomising the
internus).
February 27, 1900. — Stitches removed.
March 29, 1900. — Patient has t° esophoria in distant
vision, perfect orthophoria in near vision, binocular
prism abduction 5 . Patient never has diplopia
now.
June 18, 1902. — Patient has not been seen to cross
her eyes since the operation, and she has had no
diplopia. She is quite free from headaches now. She
has, of course, not worn glasses since the operation.
Captain P., aged about 30, consulted me on July 11,
1899. He had always suffered a good deal from head-
HETEROPHORIA
195
aches, and had had occasional momentary diplopia,
but had never been told that he squinted. Both the
headaches and the diplopia had been more frequent
since he had "fever" in India four years previously.
He had had his eyes examined several times, and
had once been ordered reading glasses, but they had
done no good.
Retinoscopy showed that he had no notable refrac-
tive error. On examining the motor balance of his
eyes, he was found to have left hyperphoria 2^°. His
right superduction and left superduction were each
scarcely i°. His right subduction and left superduc-
tion were each 5 . Excursions of each eye separately
were quite full.
August 3, 1899. — On repeating the examination, I
got precisely the same results. As there was no refrac-
tive error which would necessitate glasses, I did not
wish to burden him with prisms, I therefore advised
operation.
August 14, 1899. — I performed complete central
tenotomy of the left superior rectus, after the method
described on page 216. The after treatment consisted
only of a shell and a pad of gauze worn over the L. E.
for a few days, and bathing with boric lotion.
August 29, 1899. — Wound healed and eyes perfectly
comfortable. There is now right hyperphoria of less
than i°.
July 11, 1902. — Patient has been free from head-
aches and the occasional diplopia since the operation.
There is now no measureable degree of heterophoria.
The streak of light with the rod before the R. E. is
at the upper part of the flame, showing left hyperphoria
of less than £°.
Mr. S. H. — I saw quite recently an exceedingly
instructive case, a gentleman aged 20, sent me by Dr.
Bolton Tomson. From early childhood until one
year ago, the patient had suffered from severe head-
196
HETEROPHORIA
aches coming on towards the end of the day. He had
occasional diplopia, one image being over the other.
He also had frequent attacks of typical migraine.
During the last year, he has seen double constantly,
and the right eye has squinted downwards. He can
still, by a great effort, overcome the deviation and
blend the images. The diplopia is so intense that he
is only comfortable when one or other eye is covered.
But since the hyperphoria gave place to an actual
deviation, the headaches and migraine have completely
disappeared.
There is no important refractive error. R. E. deviates
downwards (or L. E. upwards) 8°. Either eye deviates
outwards 5 . Prisms of this strength give binocular
vision with orthophoria.
I propose to advance the L. inferior rectus muscle,
which I have no doubt will result in cure of the whole
trouble. If this operation had been performed many
years ago the patient would have been spared much
unnecessary suffering.
Insufficiency of Dynamic Convergence.
This is not a heterophoria, but it is convenient
to discuss it in this chapter.
There has been much confusion on the subject
of insufficiency of convergence, because authors
have not clearly distinguished between static and
dynamic convergence.
A person whose visual apparatus is normal has
no static convergence at any time ; in distant
vision he exercises no dynamic convergence ; in
near vision his dynamic convergence exactly
suffices to cause both visual axes to be directed
to the near object. If his dynamic convergence
INSUFFICIENCY OF DYNAMIC CONVERGENCE 197
were excessive,' there would be a tendency to con-
vergent squint in near vision ; if it were insuf-
ficient, he would have difficulty in maintaining
convergence, as in reading, for instance, for any
length of time.
A person who has a convergent squint, which
persists after correction of any refractive error,
has an unchecked static convergence ; one who
has esophoria has a static convergence which is
kept in check by constant muscular effort, 1 evoked
by the desire for binocular vision. Static con-
vergence is a minus quantity in divergent squint.
In exophoria there is a minus static convergence
which is neutralised by an abnormal effort of
dynamic convergence. In these cases the power
of dynamic convergence may or may not be
normal.
A patient, therefore, who has exophoria in
distant vision and the same degree of exophoria,
or less, in near vision, cannot properly be said to
have insufficiency of convergence. This dis-
tinction between exophoria and insufficiency of
dynamic convergence is of supreme practical
importance, because the treatment of the two
affections differs entirely. In the former case, if
any treatment be required at all, operation is
usually necessary ; in the latter, operation is al-
1 This " without prejudice " to the much-debated question
of the existence of a cerebral centre for divergence.
H
198 INSUFFICIENCY OF DYNAMIC CON VERGE NCE
ways contra-indicated, and benefit may often be
obtained from exercises.
Insufficiency of dynamic convergence, apart
from neuropathic cases, is not common.
The symptoms produced by insufficiency of
convergence are pain in the brow after reading,
and a tendency to hold the book at a long dis-
tance from the eyes (apart from any error of
static or dynamic refraction).
Convergence being a voluntary act, the extreme
degree of which any individual is capable will
vary from time to time, according- to the state of
his health and the amount of energy he is able to
put forth at the moment. Elaborate instruments
for determining the near point of convergence
are, therefore, not required. Moreover, this
information is not of much practical use.
The best procedure is to test the horizontal
motor balance of the eyes, first in distant vision.
and then at ten inches. If there is no more
exophoria, or no less esophoria, in near vision
than there is in distant vision, the patient has no
insufficiency of convergence. If the patient has
orthophoria in distant vision and exophoria in
near vision, or if there is more exophoria, or less
esophoria, in near than in distant vision, he has
insufficiency of dynamic convergence of a degree
equal to the difference.
In an uncomplicated case of insufficiency oi
convergence, exercises should be tried. The
INSUFFICIENCY OF DYNAMIC CONVERGENCE 199
following procedure is as good as any : — Any
error of static or dynamic refraction is corrected
by glasses. The patient begins reading a book
at the ordinary distance. Then, while still read-
ing, he gradually brings the book nearer his eyes
until the print begins to be blurred. He then
slowly removes the book to the ordinary reading
distance. This is repeated. At about every
tenth line he looks into the distance for a moment,
in order to completely relax his convergence.
Two or three pages should be read in this way,
three or four times a day for a month. This
simple plan has given quite as good results as the
more elaborate methods which I have tried. This
is perhaps because the patient finds it more con-
venient to carry out, no special apparatus being
required.
It has been objected that the accommodation is exer-
cised at the same time as the convergence. I do not
think that it would be advisable, in young subjects at any
rate, entirely to dissociate dynamic convergence from
the effort of accommodation with which it is normally
always associated. But if it should seem advisable to
relieve the strain on the accommodation during the
exercises, this may be done in either of two ways — the
patient may wear convex glasses so as to exercise less
accommodation with a given amount of convergence,
or, what comes to the same thing, he may wear prisms,
apex in, so as to exercise more convergence with a given
amount of accommodation.
These rhythmic exercises do not increase the
power of the ocular muscles (any more than voice
200 INSUFFICIENCY OF DYNAMIC CONVERGENCE
training increases the power of the laryngeal
muscles), so they do not in the least diminish
exophoria in distant vision. But they often much
improve the power of dynamic convergence, by
teaching the nervous apparatus to respond more
readily to the will.
In a case in which exercises have failed and
the symptoms are troublesome one may, as a
pis aller, order prisms, apices out, for near vision.
201
CHAPTER XII.
OPERATIONS ON THE EXTERNAL OCULAR
MUSCLES.
The operations commonly performed on the
muscles of the eye are advancement and tenotomy.
Either of these measures may be employed alone,
or advancement of one muscle may be combined
with tenotomy of its opponent.
The indications for these operations are fully
discussed in previous chapters.
Advancement.
Very many different methods of advancement
of a rectus muscle have been described. I have
tried many of these repeatedly, also two methods
of shortening the tendon by folding it upon itself.
None of these has proved entirely satisfactory.
With practice, one can always make sure of
inserting the sutures firmly in the tough fibrous
tissue near the margin of the cornea, without
putting in the needle dangerously deeply. The
difficulty is with the end of the sutures attached
to the muscle. I found that two of these methods
of operating gave better results than the others.
In one operation, three or four sutures are simply
202 OPERATIONS
passed through the tough circumcorueal tissue,
and through the muscle, and tied. If these
sutures hold for a week, the results are permanent.
But the muscle end of the suture often cuts its
way through in three or four days. And in any
case, one has to produce an over effect at the time
of the operation, to allow for slacking of these
sutures, so that precision is not attainable by this
method. In the other operation, the sutures are
knotted on the muscle, either in one or two parts.
This nearly always gives good immediate results,
but a very large proportion of the cases relapse
within a few weeks. This is probably due to the
fact that the muscle atrophies in front of the
ligatures, and so is only attached to the globe
by its lateral expansions, which subsequently
stretch.
I devised the following operation with the
object of combining the advantages and avoiding
the disadvantages of the two methods to which I
have just referred.
The Author s Advancement Operation.
In this operation a firm, unyielding hold is got
for the sutures at each end, so that any desired
degree of rotation of the eyeball may be produced.
For moderate deviations, I advance a muscle
without tenotomising its opponent. F"or squints
of very high degree, I usually first tenotomise
the opposing muscle to avoid refraction of the
OPERATIONS
Fig. 29.
?.;
!04
dobe.
OPERATIONS
The anatomical relations of the advanced
muscle are disturbed as little as possible. As
the middle part of the muscle is not included
Fig. 34.
in the sutures, its main blood supply is not
interfered with. The immediate effect produced
is the final result.
OPERATIONS 205
Instruments. — The ordinary advancement in-
struments are required : Speculum (fig. 29),
straight blunt-pointed scissors (fig, 34), fixation
forceps with projecting teeth which take a firm
hold of the sclerotic (fig. 36), Prince's advance-
ment forceps, right and left (figs. 30 and 31), or
the smooth probe-pointed forceps (fig. 32), needle
holder (fig. t,^), needles, and thread ; and if a
tenotomy is to be done at the same time, a
tenotomy hook also (fig. 35). The needles I use
are made for me by Messrs. Weiss and Son.
They are small, curved needles with large eyes.
They must be very sharp. The jaws of the
needle holder which I use (fig. ^t,), are curved
transversely to fit these needles. Flat jaws, how-
ever small, are apt to break a curved needle.
The advancement forceps shown in fig. 32, being
smooth and probe-pointed, is easier to introduce
than the ordinary form of Prince's. Both blades
being alike, only one forceps is required instead
of two. The spring is strong so that the smooth
blades show no tendency to slip under any strain
to which one ought to subject the tissues.
The blunt instruments are sterilised by boiling
for five or ten minutes in water containing a little
washing soda. The scissors are boiled for about
a minute. The eyes of new needles are cleared
with the point of a sewing needle. The needles
are then boiled for not more than a minute, before
being threaded. 1 used to use only new needles,
206 OPERATIONS
to ensure their being as sharp as possible. I find,
however, that it is quite easy to sharpen them on
a fine oiled stone ; even new needles can be much
improved. They should then be kept in a flannel
book ; the paper in which they arc sold is apt to
injure delicate points.
The suture material is a very important detail.
It should be thick. The thin stuff sold as " eye
silk" cuts like a knife. I use thick black silk
prepared as follows : A reel of the silk is wound
loosely round a winder (made by bending up a
piece of wire). It is boiled in water, to sterilise
it and to remove the superfluous colouring
matter. It is then dried before a fire. The end
of the silk is then threaded through a large glass
bead. The glass bead is then dropped into a
glass beaker containing a very hot mixture of
white beeswax, three parts, and white vaseline,
five parts. The whole of the silk is drawn
through the boiling mixture, and is wound on
a large glass reel. It is kept in a sterilised
glass jar, always ready for use without further
preparation.
In preparing for the operation, a piece of the
silk, about a foot long, is drawn out of the jar with
sterilised forceps ; it is threaded through the
sterilised needle as far as its middle. The two
halves of the waxed silk are then twisted together
into a single cord. Two of these threaded needles
;ire required. The part of the suture which meets
OPERATIONS 207
with the greatest resistance in passing through
the tissues, is that near the eye of the needle.
The thread must be double here in any case, so
one may as well have the benefit of the double
thickness throughout. The wax-soaked thread is
sufficiently stiff, at the ordinary temperature of the
air, to abstain from tying itself into undesired
knots during the operation, but at the body tem-
perature it is quite supple. It glides easily and
with a minimum of damage to the tissues— like
a well greased catheter. It is practically non-
absorbent— an important point in a region which
cannot be absolutely aseptic.
Anesthesia. — For young children a general
anaesthetic, preferably chloroform, is necessary.
For older patients a local anaesthetic is sufficient.
I use the crystals of hydrochlorate of cocaine,
applied twice before the operation at intervals of
about five minutes. During general anaesthesia
the eyes usually diverge, so that one has to
remember the angle of the squint and produce
approximately the effect required. Under a local
anaesthetic there is no such divergence, so that
one can gauge exactly the extent to which the
muscle is to be advanced. For this reason, I
never operate under general anaesthesia unless I
can rely upon a trained fusion faculty to do the
fine adjustment.
The operation— -The hands of the surgeon
and nurses are sterilised. The patient's face is
2o8 OPERATIONS
thoroughly cleansed. The conjunctival sac is
irrigated with sterilised saline solution (60 grains
to a pint of water). If the lacrymal apparatus
and conjunctiva are not perfectly healthy, the
operation is postponed until they are. Just after
the irrigation, and from time to time during the
operation, a few drops of supra-renal gland extract
are instilled. 1 use Parke Davis and Co.'s adre-
nalin chloride solution. The vascular constriction
caused by the extract makes the operation blood-
less or nearly so, so that one is not impeded in
one's work by the necessity for constant sponging.
The patient lies on the table in a good light,
with his feet towards the window. His lids are-
held open by the speculum. The surgeon, stand-
ing behind the patient's head, grasps the con-
junctiva with the toothed forceps, while, with the
scissors, he makes a straight vertical incision
through it about half an inch long. The middle
of the incision is close to the corneal margin. A
similar incision is then made through the capsule
of Tenon. The conjunctiva and capsule then
retract, or, if necessary, they are pushed back, so
as to expose the insertion of the tendon. If the
angle of the squint is of high degree, the vertical
incision through the membranes is made curved
instead of straight, the convexity of the curve
beim>" towards the cornea. This is to allow the
membranes to retract more freely. One blade of
the advancement forceps is now passed under the
OPERATIONS
:oq
tendon, after the manner of a tenotomy hook, the
other blade being superficial to the conjunctiva.
The forceps is now closed, so that tendon, capsule
of Tenon, and conjunctiva are all firmly clamped
together, with their relations undisturbed except
tor the retraction of the membranes. The tendon,
and a few little fibrous bands beneath the tendon,
are now divided with scissors, at their insertion
into the sclerotic. The advancement forceps,
holding the tendon, capsule, and conjunctiva, can
now easily be lifted up so as to get a good view
of the under side of the muscle.
One of the needles is then passed inwards at
A, through conjunctiva, capsule, and muscle. It is
then again passed through muscle, capsule, and
conjunctiva, and brought out at B. The bight
of the thread thus encloses about the lower fourth
of the width of the muscle, together with its ten-
dinous expansions and capsule and conjunctiva.
The other needle is similarly entered at A', passed
through conjunctiva, capsule, and muscle, and
brought out at the under side of the muscle. It
is then entered again at the under side of the
muscle and brought out through the conjunctiva
at B', the bight of this suture thus enclosing
the upper fourth of the width of the muscle, &c.
The object of inserting both sutures, before
proceeding further with either, is that they may
be symmetrically placed. The ends of the
thread from A' and B' are then knotted tightly
2IO
OPERATIONS
at C. The end bearing the needle is then
entered at D, and passed through conjunctiva,
capsule, and muscle, and carried beneath the
lower blade of the advancement forceps nearly to
the corneal margin. The needle is here passed
Fig. 37.
through the tough circumcorneal fibrous tissue,
and brought out at G'. The two ends of the
thread are then temporarily tied loosely, with
a^ single hitch, at H. The first suture is then
similarly completed. The anterior part of the
muscle and capsule and conjunctiva are then
OPERATIONS 2 I I
removed, by cutting them through with scissors
behind where they are grasped by the advance-
ment forceps. The gap is then closed by tight-
ening and securely tying each suture at HH, so
that the eyeball is rotated in its correct position,
and the anterior end of the muscle is brought
nearly up to the corneal margin at GG'.
In operating under cocaine, before the knots
are tied at HH, an assistant holds the globe in
the primary position with forceps, while the
patient is told to try to look away from the
operated muscle. This relaxes the muscle while
it is being drawn forward by the sutures. The
sutures are then temporarily secured at HH, by
the first hitch of "the surgeon's knot." The
assistant then releases the globe. The fine
adjustment is done by tightening or loosening
the hitches at HH, the result being checked by
the mirror test or by the reflection of a candle
flame on the corneae. The surgeon's knots at
H H are then completed.
The longitudinal position, on the muscle, of the
loops ABC and A' B' C, varies approximately
according to the degree of rotation required.
In operating under cocaine, the immediate
effect is the permanent result. No over-correction,
therefore, is necessary. In operating under general
anaesthesia, one has to bear in mind the angle of
the deviation and produce approximately that
decree of rotation.
2 I 2 OPERATIONS
After the operation, the eye is irrigated with
sterilised saline solution, a little boric ointment
smeared on the edges of the lids, and a gauze pad
applied.
After-treatment. — The eye is irrigated and
dressed every day. The more quiet the eye is
kept, during the first few days, the more quickly
will the wound heal. I prefer, therefore, to keep
the patient in bed, with both eyes bandaged for
the first four or five days. After this time his
unoperated eye is uncovered, and atropised to
prevent any effort of accommodation. His spec-
tacles, if he has any, are put on over his bandage.
It is a good plan to stick two pieces of postage
stamp paper on the lens before the unoperated
eye, so as to leave a narrow vertical slit between
them. If the patient looks only through the slit,
he can look up or down, but does not make any
horizontal or accommodative movements, which
might retard the healing of the wound. The
stitches are removed on the eighth day. The
bandage is discarded two days later.
Musculo- capsular advancement. — In many cases
of neuropathic divergence, and in some old cases
of divergence following tenotomy of an internal
rectus, it is advisable to bring forward the capsule
of Tenon and conjunctiva as well as the enfeebled
muscle. These membranes have little elasticity,
so that movement in the opposite direction will
be restricted.
OPERATIONS
213
Seize the conjunctiva and capsule of Tenon just
above or below the insertion of the muscle to be
advanced. Snip through these membranes with
scissors. Introduce one blade of an advancement
forceps, and hook this blade under the tendon,
after the manner of a tenotomy hook. Close the
forceps. The membranes and tendon are thus
clamped together, so that no retraction of the
former is permitted. Now make the long vertical
incision near the corneal margin, and proceed
with the advancement as already described.
Secondary advancement. — Not infrequently a
patient presents himself with one eye widely
divergent as a result of tenotomy of an internal
rectus muscle. Usually, an excellent cosmetic
result may be obtained by advancing the retracted
muscle, even after many years. Sometimes, how-
ever, the muscle is much atrophied from disuse.
The conjunctiva and capsule of Tenon will be
matted to the globe in the neighbourhood of the
former insertion of the muscle, or the eyeball may
be quite destitute of covering in this region.
Grasp the membranes, with toothed forceps, well
above or below the scarred area, and, with the
scissors, separate them from the nasal side of the
eye. A squint hook may be of assistance in this.
If the muscle is not found attached to some
portion of the anterior segment of the globe it
is of no use searching for it with a squint hook far
back. It is never found attached to the posterior
15
214 OPERATIONS
hemisphere. Seize the coverings of the eye in
the region of the sunken caruncle, pull them
forward, lift them up. The muscle, or what
remains of it, will be seen on their under surface.
I think that, after tenotomy, the tendon fails to
become reattached directly to the globe far more
often than is generally supposed. If the muscle
be fairly good it may be advanced in the ordinary
way. If, however, it be much atrophied, a musculo-
capsular advancement is preferable. The muscle
and membranes are seized with toothed forceps
and drawn between the jaws of an advancement
forceps. The surface to which the muscle and
membranes are to be attached must be well
refreshed.
Tenotomy.
There are several slightly different methods of
performing this little operation. The following is
as good as any other. The instruments required
are speculum (fig. 29), straight blunt-pointed
scissors (fig. 34), tenotomy hook (fig. 35), and
fixation forceps (fig. 36). The patient lies on a
table. Both eyes are cocainised. The eye to be
operated upon is irrigated with sterilised saline
solution, and a drop of supra-renal extract is
instilled. In operating on the left internal rectus,
it is more convenient to stand in front, and on the
left of the patient. In tenotomising any of the
other recti, I prefer to stand behind the patient's
head. The speculum is inserted, if the muscle to
OPERATIONS 2 15
be tenotomised be one of the external or internal
recti. In the case of a superior or inferior rectus,
the lids should be held open by the fingers of an
assistant. Tell the patient to look in a direction
opposite to that of the tendon to be divided, so as
to bring its insertion well forward. With the for-
ceps, pick up the conjunctiva over the insertion of
the tendon, and, with the scissors, make an incision,
about one-third of an inch long, in a direction at
right angles to that of the tendon. Now divide
the capsule of Tenon in the same way. This
brings the insertion of the tendon into view.
While the forceps still hold up the cut edge of the
capsule, make a few short snips with the scissors
near one border of the tendon, until the point of
the scissors is felt to slip freely back without
encountering any resistance. Now lay down the
scissors, and take up the hook in the right hand.
Pass the point of the hook into this incision, and
hook it round the insertion of the tendon, until
it appears at the other border. During this
manoeuvre, the point of the hook should be kept
in contact with the sclerotic. Now lay down the
forceps, and transfer the hook to the left hand.
Take care to avoid any dragging with the hook,
as this causes pain. With the scissors, cut
between the point of the hook and the globe,
until the tendon is divided at its insertion, and
the hook comes away. It is usual to reintroduce
the hook, to seek for any fibres of insertion which
2l6 OPERATIONS
may have escaped division. It is not necessary
or advisable to suture the conjunctiva, unless the
conjunctival incision is unusually large.
After the operation, there is a very considerable
defect of movement in the direction of action of
the tenotomised muscle. This, to some extent,
subsequently disappears. The average effect of a
tenotomy of the internal rectus is 13 , and of the
other recti less than half this amount. But it
varies within extremely wide limits.
A pad and bandage should be worn for the first
forty-eight hours, after which it may be discarded.
The eye should be bathed with boric lotion, three
or four times a day, until the wound is healed.
Complete central tenotomy . — In America, partial
tenotomies are very commonly performed. I
believe these to be useless, as, until the whole of
the tendon proper has been divided, no appre-
ciable effect is produced. But the neat and
precise method by which these partial tenotomies
are performed is very well worth copying. By
this method, the tendon itself may be completely
divided, leaving its lateral expansions absolutely
intact.
The patient is prepared as for an ordinary teno-
tomy. The forceps, scissors, and tenotomy hook
required are those of Stevens (figs. 40, 3$, and 39).
The surgeon, standing behind the patient's head,
seizes, with the forceps, the conjunctiva over the
tendon near its insertion. A transverse incision
OPERATIONS
217
of sufficient length is made through the con-
junctiva. The capsule of Tenon is now similarly
incised, to an extent just sufficient to expose the
tendon. The central fibres of the tendon are
next grasped by the forceps, and a button-hole is
snipped through the tendon with the scissors.
The forceps being laid aside, the small tenotomy
2l8 OPERATIONS
hook is introduced through this button-hole, with
its point turned towards one border of the tendon,
Half the tendon is cautiously snipped through on
the hook, from the centre towards the edge. The
point of the hook is now turned round, and the
other half of the tendon similarly divided.
When the hook is first introduced through the
button-hole, on lifting it up, the tension of the
tendon is felt. When the whole of the tendon
proper has been divided, considerable tension is
still felt, by means of the hook, at the edges
of the wound. This resistance is due to the
lateral expansions of the tendon. These should
on no account be divided, as it is upon the pre-
servation of these lateral expansions that the
safety of this operation depends. Sometimes it
is impossible to define exactly the edge of the
tendon, owing to its gradually merging into its
lateral expansions. In such a case, one has to be
guided by the degree of tension felt by the hook.
No after-treatment is required beyond frequent
bathing with boric lotion or sterilised saline
solution.
This operation appears to be a safe one when
judiciously employed, but the effect produced by
it is small— about 6° or y° in the case of the
internal rectus, and 3 in the case of the superior
rectus. It varies very little in different cases, and
shows no tendency to increase with time. I have
usually seen a slight decrease after a few weeks.
219
APPENDIX.
Congenital Amblyopia.
Table VI. shows the degrees of refractive error and
the visual acuity in the twenty-three cases of congenital
amblyopia described in Chapter V.
Table VI.
Better Eve.
Worse Eye.
Refractive error.
Vision.
Refractive error.
Vision.
Lower
Higher
Lower
Higher
meridian.
meridian.
meridian.
meridian.
+ 1
+ 1
t
+ 2-5
+ 4
A
— 0-5
O
|
-0-5
+ 4-5
A
+ T5
+ i-5
§
+ 1
+ 3-5
ft
— i"5
+ 2
s
— 2
+ 2-5
A
+ 2
+ 1
6
+ 2
+ 5
A
+ 2
+ 1-25
1
+ 5-25
A
+ L25
+ 1-25
§
+ 5
+ 7
A
+ i-5
+ i-5
1
+ 5
+ 6-5
A
+ 4
+ 4
I
+ 5-5
+ 8-5
*
+ o- 5
+ 0-5
f
+ 1
+ 1
35
+ o-5
+ 0-5
6
+ 4
+ 6
A
+ i
+ 1-25
f
+ 1
+ 4-5
A
+ 3-5
+ 3'5
|
+ 2
+ 6-5
A
+ i-5
+ 175
§
+ i-5
+ 475
A
+ o- 5
+ 0-5
6_
— 1
+ 3
A
+ i
+ 1
|
+ 1
+ 4
ft
o
f
+ 4
+ 6-5
ft
+ 3
+ 3-5
6
+ 3
+ 7
A
+ i
+ 1
8
— i'5
+ 2-5
ft
+ 075
+ 1
9
+ 3
+ 5-5
A
+ 2
+ 2
6
5
+ 2
+ 6-5
A
+ 0-5
+ 0-5
9
+ 1
+ 4-5
A
+ 0-25
+ 075
I
+ T5
+ 5-5
ft
220
APPENDIX
Table VII. shows the refractive error and the visual
acuity of the eleven cases in Table III., Chapter V.,
which had an amblyopia of T 6 « or higher. The visual
defect in these cases also is almost certainly congenital.
Table VII.
Fixing Eye.
Deviating Eye.
Refractive error.
Vision.
Refractive error.
Lower
Higher
Higher
Lower
Vision.
Meridian.
Meridian.
Meridian.
Meridian.
+ 2
+ 2
|
+ i-5
+ 5-5
A
+ 3"5
+ 4
5
+ 3-5
+ 6
A
+ i-5
+ i-5
§
+ i-5
+ 5
A
+ 4
+ 4'5
1
+ 2
+ 5-25
&
+ 2
+ 3
S
+ 2
+ 7
&
+ 1
+ 1
I
+ 1
+ 3-5
A
+ 2-5
+ 3
?
+ 0-5
+ J5
A
+ 3
+ 3
I
+ 3-5
+ 7'5
A
+ 0-5
+ 0-5
f
— 1
+ 275
A
+ 275
+ 3-5
g
+ 1
+ 5"5
A
+ 1-25
+ 1-25
6
+ 4-5
+ 8-5
A
Prisms and Decentred Lenses.
There are several systems of numbering prisms. In
ordering a prism it is necessary, therefore, to specify
which system one uses. In this book the strength of
a prism is expressed by the number of degrees which
it deflects a ray of light. This " deviating power " is
about half the geometrical angle (the angle between
the two plane surfaces).
A prism causes mal-projection, and chromatic dis-
persion of white light. Clinically, mal-projection is
avoided by dividing the prism between the two eyes.
For instance, in a case of right hyperphoria 2 , if one
wished to correct l£° of the error, one would order a
prism : , ! ° apex up, before the right eye, and a prism
of the same strength, apex down, before the left eye.
APPENDIX
221
Chromatic dispersion is not noticeable in a prism which
does not exceed 2° deviating power.
A pencil of parallel rays which traverses a spherical
lens at its optical centre, is made convergent or diver-
gent. A pencil of rays, traversing a lens towards its
periphery, is deflected in addition (as by a prism)
towards the axis of a convex lens away from the axis
of a concave lens.
Glasses containing prisms in combination with
spherical and cylindrical lenses are expensive, because
they must be specially ground — the optician cannot
prepare them from his stock. But if the patient has
to wear fairly strong lenses, and if the required pris-
matic effect is small, this may be secured by decentring
the spectacle glass. That is, the optician, instead of
cutting the spectacle glass from the middle of one of
his ready-ground lenses, cuts it from one side. This
is much cheaper. The effect of decentring a cylin-
drical lens, in a direction at right angles to its axis,
is the same as that of decentring a spherical lens. In
a lens of the ordinary stock size, there is room to
decentre a medium-sized spectacle glass about 3 mm.,
i.e., a total of 6 mm. in the two eyes.
The following table, prepared from Dr. Maddox's
formula, shows the prismatic effect of decentring
lenses.
2 mm.
3 mm.
4 mm.
5 mm.
6 mm.
2 D.
14'
21'
27'
35'
41'
3 D.
2l'
31'
41'
52'
1° 2
4 D.
27'
41'
55'
i° 10
1° 22'
5 D.
35'
52'
i° 10'
i° 26'
i°43'
6 D.
4i'
1° 2'
i° 22'
i°43'
2° 4'
7 D-
48'
1° 12'
i°36'
2°
2° 24'
8 D
55'
1° 22'
i°5°
2° I 9 '
2 45'
222 appendix
Results of Fusion Training.
In the earlier cases I had not perfected my methods
of fusion training, and in recent cases sufficient time
has not yet elapsed to show that the results are per-
manent. I therefore give the results of fusion training
in ioo consecutive cases, beginning January, 1896.
Five were what 1 have called essentially alternating
squints, in which I was unable to get even simulta-
neous vision of the two object slides. In 17 cases the
patients were more than 6 years of age. I got a
moderately good result in two of these, and failed in
the other 15. I scarcely ever now attempt fusion
training after 6 years of age. Of the remaining 78
cases, which alone were suitable for fusion training,
I failed in 12 cases (owing to intractability of patient,
irregularity of attendance, or apparent absence of the
power acquiring fusion) ; in seven cases the result was
only moderate, and in 59 cases a good amplitude of
fusion was developed. In two of these cases the
parents refused advancement which was necessary to
complete the cure ; four cases have been lost sight of ;
the remaining 53 cases are perfectly and permanently
cured.
Results of Advancement Operations.
In performing advancement I have, since 1898,
relied exclusively upon the method described in Chap-
ter XII. I therefore give results of 100 consecutive
advancement operations, beginning January, 1899. I
have re-examined most of these cases within the
present year (1906).
By primary advancement I mean advancement of
a muscle which had not previously been operated
upon. In some of these cases the opposing muscle
had previously been tenotomised by some other sur-
geon. By secondary advancement I mean operation
APPENDIX
223
upon a muscle which had previously been tenotomised
or unsuccessfully advanced.
In cases in which the fusion sense has been fairly
well developed, but in which the deviation persists,
the object of operation is to put the eyes into such
a position that the patient will have binocular single
vision. If the fusion sense cannot be developed, one
aims at removing the visible deformity. Cases which
come up to this standard I have classified as success-
ful. Those which do not I have called unsuccessful,
although in all these cases there was considerable
improvement.
Eighty-six operations were performed under cocaine
and 14 under chloroform.
The 100 cases consisted of : —
Secondary
The 77 cases of primary advancement of external
rectus included one case of congenital paralysis of
external rectus and two cases in which the muscle
was atrophied. In these three cases, though a per-
fect result was not to be expected, musculo-capsular
advancement, combined with tenotomy of the oppos-
ing muscle, produced considerable improvement in
the appearance.
Of the 74 remaining primary advancements of
external rectus, 66 were successful ; in three other
cases a second operation 1 proved successful ; in one a
second operation was recommended but was refused ;
in four cases, though the results did not satisfy me,
1 I have not included these three cases in the list of secondary
advancements recorded below.
external
rectus
... 77
internal
„
8
inferior
„
1
external
„
4
internal
„
9
superior
„
1
224 APPENDIX
the patients were quite satisfied, so, as there was no
fusion sense in any of these four cases, I did not urge
further operation. In 17 of these 74 cases the internal
rectus was tenotomised at the same time.
Of the eight primary advancements of internal
rectus, two were old myopic divergent squints, and
two were neuropathic divergent squints with some
fusion sense. These were successful. The remaining
four were neuropathic divergent squints with no
fusion sense. Considerable improvement in appear-
ance was produced in these four cases, but the results
were far from perfect (see p. 138). The external rectus
was not tenotomised in any case.
The primary advancement of inferior rectus was
in a case of vertical deviation of high degree with
absence of fusion sense. I succeeded in removing
the deformity.
The four secondary advancements of external rectus
were in cases in which some one had unsuccessfully
attempted advancement. In one case I succeeded.
In the other three the previous mutilation 1 of the parts
rendered a perfect result impossible.
The nine secondary advancements of the internal
rectus were all cases in which tenotomy of this muscle
had been followed by divergence of the eye. I was
responsible for two of these tenotomies. Five of these
secondary advancements were successful ; in three
the condition was improved ; in one there was no
improvement.
The secondary advancement of the superior rectus
has already been described (Case D, 227, p. 153).
1 If a suture lias been tied on the muscle, including its whole
width, the muscle in front of the ligature atrophies just as surely
as if it had been cut off with scissors.
If a surgeon in advancing a muscle has isolated it from its
overlyin- membranes and its Literal expansions, if one has to
operate again upon this muscle one finds a shapeless mat of
muscle and scar tissue.
APPENDIX
225
The Deviometer (p. 89).
The patient's eye is only two feet from the instru-
ment. In looking at the button above the light he
will, therefore, exercise a dynamic convergence pro-
portionate to that distance. It has often been sug-
gested to me that this would cause the degree of a
convergent squint to appear greater than it really is.
This is not the case, because the surgeon's eye is at
the same distance, just above the zero of the scale.
This is easily demonstrated by experiment with a
normal-sighted person. When he looks at the button
both visual axes converge to this point. The surgeon
places his eye at the same distance — just above the
button — so that he sees the vertical lines of light
occupying symmetrical positions on the corneas of
the observed person, showing that the latter has no
squint. If the observed person could look at the
button with one eye, without exercising any dynamic
convergence (keeping his visual axes parallel), he
would appear to the surgeon to have a divergent
squint — in fact, he would have a divergent squint for
that distance.
No adjustments are required except that the 60 cm.
string must be kept taut. As the scale is flat, instead
of a curved arc, a slight lateral movement on the part
of the patient introduces no appreciable error. The
height of the patient's eyes above the tables makes no
difference.
Details of construction. The woodwork can be made
by any carpenter for a few shillings. The following
measurements have been found satisfactory : —
The pedestal, 10 inches wide, 5 inches deep, from
before backwards, i\ inches high.
The upright board, height 13 \ inches (11 inches
above pedestal), width 5 inches, thickness f inch.
The arm is pivoted at one end by a bolt which
passes through the upright board. There is a chock on
226
APPENDIX
each side, on one of which it rests. It is swung over
to either side as required. This arm is of hard wood,
27 inches long, 2 inches wide, T \ inch thick. It is
painted black in front. A long strip of white paper or
celluloid, about half an inch wide, has marked on it the
tangents to degrees at the distance of 60 cm. This
strip is pasted on the back of the arm, with the zero
of the scale at the pivot hole.
The tangents to degrees at 60 cm. are —
2*1 cm.
4'2 „
6-3 „
8-4 „
io-6 „
12-8 „
15 »
I7'2 „
18°
20°
■79°
24°-
26°-
28° •
30
19-5 cm.
21-8 „
24-2 „
267 „
29-3 »
319 >.
■347 „
3TS »
34 — 40-5 cm.
3 6°-43-6 „
38 — 46-9 „
40 — 50-3 „
42 — 54 »
44°— 57'9 .,
46 — 62-6 „
48 — 667 „
In inserting the bell push only one wire is cut,
the other being left intact. The instrument is made
by Messrs. Bonnella and Son, 58, Mortimer Street,
London, W.
Modifications of the Amblyoscopk.
Dr. ERNEST Maddox uses a quickly acting screw,
instead of the short slot in the brass arc. This ad-
mits of delicate adjustment, which is an advantage in
testing the horizontal breadth of fusion.
Dr. Freeland Fergus employs a method of illumi-
nating the object slides which is certainly more compact
than the apparatus shown in fig. 12, and is probably
equally efficacious. " Immediately behind the parts of
the Amblyoscope into which the pictures arc placed,
there is a stout metal collar from which a curved piece
of metal is carried in front of the pictures. To each
of the two pieces of metal an electric lamp of about
three-candle power is attached. From each of the two
lamps a lead is taken to a rheostat, so that the amount
of illumination of each is thoroughly under control."
APPENDIX
227
Dr. Maitland Ramsay has substituted total-re-
flecting prisms for the mirrors (" Ophthalmoscope,"
vol. 3). These are, of course, very perfect reflectors,
but very expensive. He has also devised an improved
lighting apparatus. " The lighting is arranged by
means of two small lamps, one fixed immediately
Fig. 41.
Fig. 42
behind each picture in the Amblyoscope. The degree
of illumination is varied and regulated by a sliding
bridge-resistance, which can be adjusted most delicately
and which, while it takes resistance from the circuit of
one lamp and so increases its brightness, at the same
time throws more resistance into that of the other and
brings about corresponding diminution of its brilliancy.
228
APPENDIX
The illustrations show the arrangement, which has
been carried out by Mr. Trotter, 40, Gordon Street,
Glasgow."
Dr. Nelson Miles Black has added a vertical
screw adjustment, by means of which one tube can be
moved above or below the plane of the other, in order
more readily to adapt the instrument to cases of squint
in which there is a vertical deviation. By means of
this ingenious device, one may, in a case of obstinate
suppression, call attention to the second image by
temporarily throwing it above or below the plane of
the other.
Advancement Forceps.
Messrs. Weiss and Son have made for me an
advancement forceps on the Prince model, which
seems perfect. There are no spikes, the blades are
smooth and probe-pointed, so the instrument is as
KKSffllltar
Fig. 43-
easy to introduce as a tenotomy forceps. The catch
gives a firm grip and has not the same tendency as
the spring catch to get out of order. Only one forceps
is required.
229
INDEX
Abduction
Abversion ...
,, in cases of coir
Accommodation ...
ergent squint
PAGE
. 180
4
27.49
1
and convergence, association between
Advancement
,, musculo-capsular
secondary
,, results of
Ad version ...
Etiology of convergent squint ...
,, ,, author's proposition .
., ,, ,, Donder's theory
,, ,, ,, muscle theory
Amblyopia, acquired (amblyopia ex anopsia) ...
,, ,, methods of curing
„ method of preventing
,, congenital
„ in cases of convergent squint
Amblyoscope
as a test for binocular vision
,, illuminating apparatus for
,, object- slides for ...
Angle gamma
„ ,, method of measuring ...
Angle of deviation, methods of measuring
Anisometropia
,, in convergent squint
„ predisposing to squint . . .
3
201
212
140,213
... 222
4
48
54
50
... 48
66, 77
103, 105
... 105
63, 76, 219
34, 76, 220
120
16
122
123
5
94
Astigmatism
i6
in convergent squint
in congenitally amblyopic eyes
65:
5
47
57
5
45
220
230 INDEX
PAGE
Atropine, effect of ... ... ... ... ... 2
„ instilled into fixing eye only .. . ... ... 105
,, long-continued use of, for both eyes causes
extreme amblyopia in the deviating eye 70, 109, 154
Binocular vision ... ... ... ... 7, 86
,, ,, grades of ... ... ... ... 12
. r y .,, ,, in infancy ... ... ... ... 20
,, ,, tests for ... ... ... ... 14
21
3
3
196
198
84
3
25
30
48
46, 47, 61, 116
... 27
27, 28, 84
30,61
... 60
Conjugate movements of the eyes in infancy ..
Convergence and accommodation, association between
,, dynamic ...
,, dynamic, insufficiency of
,, dynamic, method of investigatin
,, dynamic, method of investigating in a
case of squint ...
Convergence, static
Convergent squint
accidentally alternating
aetiology of ...
alternating ... 30, 42
conjugate movements in
dynamic convergence in
essentially alternating
hereditary influence in
measurement of the
deviation
Convergent squint, method of investigating a case of
,, ,, method of investigating fixation of
deviating eye ...
Convergent squint, unilateral ...
unilateral, course of an untreated
case ... ... ... ... ...
Convergent squint, occasional ...
angle of
88
78
82
29
40
116
power of rotation of each eye 27, 49, 83
,, ,, spontaneous " cure " of ... ... 39
,, statistical tables showing visual
acuity of deviating eyes ... ... ... 76-77
Convergent squint, statistics showing age at which
the deviation appears ... ... ... ... ... 42
INDEX
231
PAGE
Convergent squint, statistics showing refractive
error in ... ... ... ... ... 43
Convergent squint, the question of operation in ... in
ii ,, treatment of ... ... ... 97
Cover test for squint ... 79
Cyclophoria 166, et seq., 188
,, experiments to explain the effect of ... 189
Decentration of lenses ... ... 220
Deviation, methods of measuring angle of ... ... 88
Deviometer ... ... ... ... ... 89, 225
Diplopia artificially produced 32, 87
,, in convergent squint ... ... ... 32, 33
,, monocular ... ... ... ... ... 36
,, physiological ... ... ... 9
Divergence in extreme myopia... ... ... ... 138
,, of blind eyes ... ... 139
,, secondary to tenotomy ... ... 154, 139
Divergent squint, infantile myopic ... ... ... 136
,, .» myopic . . ... ... ... 133
,, ,, neuropathic... ... ... ... 136
Dynamic convergence (see " Convergence, Dynamic ")
,, refraction (see " Refraction, Dynamic ")
Emmetropia ... ... ... ... 1
Esophoria... ... ... 166, et seq., 183
,, mistaken for occasional convergent squint
29, 183, 194
Examination of a case of convergent squint ... ... 78
Exophoria ... ... ... ... 166, et seq., 185
False macula ... 36
Fevers, specific, preceding the appearance of a
deviation ... ... ... ... 58
Fixation ... ... ... ... ... ... ... 3
,, false ... ... ... ... 36
,, in deviating eyes ... ... ... 35, 76, 77
,, in infancy ... ... ... ... ... 20
lost 36, 77
,, method of investigating ... ... ... 84
Four-dot test .., ... ,.. ,. 15
232
INDEX
Fusion, amplitude of
,, experiments showing elasticity of
,, (see also " Binocular Vision ")
,, sense, defect of, the fundamental cause of
PAGE
13. 129
10, 11
squint ...
Fusion sense, method of training
,, ,, normal development of, in infancy
,, training, results of
"Growing out of a Squint"
Hereditary influence in convergent squint
Hering's drop test
Heterophoria
Heterotropia ...
Hypermetropia ...
,, causing a tendency
squint
Hypermetropia in convergent squint
Hyperphoria
55> 60
. 118
20
. 222
• 39
60
17
164
. 168
to convergent
50,56
43
166, et seq., 186
Infancy, central fixation in ... ... 20
,, conjugate movements of the eyes in ... 20
,, development of binocular vision in ... ... 20
Infants, spectacles for ... ... ... ... ioi, 102
spurious squint of ... ... ... .. 38
Insufficiency of dynamic convergence... ... ... 196
Investigation of a case of convergent squint ... ... 78
Ivory-ball test 85
Lenses, decentration of ... ... ... ... 220
Macula, false ... ... ... ... ... ... 36
Maddox double prism ... ... ... ... ... 172
,, rod 170
,, tangent scale 91, 172
Mirror test for convergent squint ... ... 80
Muscular balance of the eyes, methods of investigating 169
Myopia 5» 43
Myopic divergent squint ... ... ... ... 133
Neuropathic divergent squint
1 36
INDEX 233
PAGE
Occlusion of fixing eye ... ... 103
Operation in cases of convergent squint
in, 144, 145, 148, 157, 159
Operations on the external ocular muscles 201
Optical correction in cases of convergent squint ... 98
Orthophoria I °4
Paralysis of external rectus muscle ... 33, 59, 81
Perimeter method of measuring deviations 93
Peripheral form vision, method of testing ... ... 64
Perspective, sense of 13, I7> I 3°
Phorometer .. ... ... ... 181
Physiological diplopia 9
Presbyopia ... ... ... •■• ••• ••• 2
Prism duction 179
Prisms and decentred lenses ... ... ... ••• 220
Pseudo-heterophoria ... ... ... 166
Refraction, dynamic ... ... ••• 2
,, investigation of ... ... ... ••• 95
,, static ... ... ... ••• ••• !
Refractive error, correction of, in convergent squint 98
,, ,, „ in divergent squint .. 135
,, ,, ,, in heterophoria ... 166
,, ,, ,, in infants ... 98. 102, 151
,, ,, in cases of convergent squint ... 43
,, ,, ,, divergent squint 133, 137
Results of advancement operations 222
,, ,, fusion training ... •• 222
Simultaneous macular perception ... 13, 128
Smith, tape method of Priestley 9 2
Spurious squint of infants ... ... ... ••• 3&
Squint, convergent (see "Convergent Squint")
Squint, divergent (see " Divergent Squint ")
or paralysis, differential diagnosis ... ... 81
,, relative frequency of ... ... ... ••• 47
Static convergence ... ... ... 3
,, refraction ... ... ... ... ••• ••• r
Subduction 180
Subversion ... ... ... ••• 3
Superduction ,,, ;rr ... ,,, ,,, ••» J 80
234 INDEX
PAGE
Superversion ... ... ... ... ... ... 3
Suppression of the vision of the squinting eye ... 31
Tangent scale of Maddox ... ... ... 91, 172
Tenotomy... ... ... ... ... ... 111, 214
,, complete central ... ... ... ... 216
,, divergence caused by ... 139, 154, 213
Vertical deviation, apparent ... ... ... 37
,, ,, true ... ... ... ... 38
Vision, binocular (see " Binocular Vision ")
Visual acuity, method of investigating ... ... 85
of deviating eyes ... ... ...76,77
,, ,, peripheral, method of investigating ... 64
Visual axis 3
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