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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, /.


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