Clinical Investigations on Squint

Part 1

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CLINICAL INVESTIGATIONS ON SQUINT

A MONOGRAPH

DR. C. SCHWEIGGER,

PROFESSOR OF OPHTHALMOLOGY AT THE UNIVERSITY OF BERLIN

TRANSLATED FROM THE GERMAN

EMILY J. ROBINSON

EDITED BY

GUSTAVUS HARTRIDGE, F.R.C.S.

LONDON J. & A. CHURCHILL 11, NEW BURLINGTON STREET 1887

TRANSLATOR'S PREFACE

The subject of Squint is so interesting that we venture to think an English rendering of this exhaustive monograph will be acceptable to many ophthalmic surgeons and students.

While adhering as far as possible to the spirit and style of the original we have not hesitated here and there to give a somewhat free translation. This has been partly necessitated by the difficulty of finding an exact equivalent in English for all the terms used in the original text.

In the German Edition the old system of inches is used. We have (with the consent of the author) altered these to the dioptric system.

E. J. R. G. H.

PREFACE

Amicus Plato, amicus Socrates, magis amica veritas. May my friends and colleagues, whose views differ from mine, read the following observations without prejudice. A fact, which does not agree with the system, is generally worth more than theory, still it is very difficult for even the most important fact to find recognition if it contradicts received opinion. For theories and dogmas are narcotics, which are necessary to men; some flatter themselves by composing them, while others content themselves by satisfying their own craving for a creed. Reasonably applied, they may be useful, but the boundary line is only too easily over-stepped. It is the task of science to observe also whether theories correspond with the progress of facts. The present reigning theory on strabismus will have to submit to various limitations; on the other hand, we are ready to leave to the scholastic science of medicine and its followers certain dogmas which remain unproved and which have nothing but the fact of their existence to recommend them.

The small compass of the following treatise proves that it was not intended to exhaust the rich literature on the subject; I have only referred to the same where it appeared to me necessary for the interest of the work in hand.

Above all, it has been my endeavour to treat the subject of this treatise (which occurs so frequently in practice) in a way intelligible to every physician, at the same time, however, to bring sufficiently into notice those facts and views which are of value to my special colleagues.

C. SCHWEIGGER.

BERLIN.

INDEX TO CONTENTS.

INTRODUCTION. PAGES

Ordinary use of the word squint and its meaning. Apparent squint. Paralytic and typical squint. Law of association. Squint angle and linear measure of the deviation. Permanent, periodic, latent, monolateral, and alternating squint 1-8

CONVERGENT SQUINT.

Donders' theory and the test of it by statistics. Limits of error in the subjective and objective determination of hypermetropia. Statistics of convergent squint. Hypermetropia and favouring circumstances. Participation of the accommodation. Preponderance of the interni and insufficiency of the externi. Nebulæ of the cornea. 9-26

PERIODIC CONVERGENT SQUINT.

In myopia, emmetropia, and hypermetropia. Intermittent squint. Accommodative squint 27-35

Part 2

CONVERGENT SQUINT IN MYOPIA 36-38

SQUINT FROM PARALYSIS OF THE ABDUCENS 39-40

HYSTERICAL SQUINT 41-43

DIVERGENT SQUINT.

Absolute and relative divergence. Statistics of divergent squint. Causes 44-49

DYNAMIC SQUINT, INSUFFICIENCY OF THE INTERNI AND MUSCULAR ASTHENOPIA.

Diplopia and power of overcoming prisms. Facultative divergence. Dynamic absolute divergence. Parallel strabismus. Relative divergence in myopia. Muscular asthenopia. Dynamic relative divergence. Treatment of muscular asthenopia 50-63

BINOCULAR VISION IN SQUINT.

Single vision in squint. Theory of exclusion. Forms of binocular vision in squint 64-74

VISUAL ACUTENESS OF THE SQUINTING EYE.

The trial of vision and its results. Appearance, diagnosis. Peculiarities and statistics of congenital defective vision. Relation of the same to defective vision in squint 75-104

CURE OF SQUINT.

Spontaneous cure. Voluntary loss of the habit. Cure of convergent squint by means of convex glasses. Strabotomy. Tenotomy. Advancement. Result of the operation and choice of methods. After-treatment by means of influence on the ocular muscles and on the accommodation. Aim of more extended results of the operation. Artificial strabismus. Operation for periodic convergent squint. Strabotomy in homonymous diplopia. Operation for squint after paralysis of the abducens. Operation for divergent squint and for periodic divergence. Degree of the result of the operation. Determination on the age best suited for operation 105-141

SQUINT

INTRODUCTION

By squinting, in the German vocabulary, is understood every oblique direction of the visual axes. We prefer that the eyes which turn towards us should do so in a straight line, and feel it to be something ugly and out of harmony, if anyone squints at us. Æsthetic feeling is, however, too individual and uncertain a guide to be laid down as a foundation for the decision of questions of medicine. Parents have repeatedly brought to me children said to squint, when frequent and careful examination of them showed normal position of the eyes and perfect binocular vision; the over-anxious parents had taken mere physiological convergence or side glances for squinting.

On the other hand, cases appear in which such a strong semblance of squinting is present, that at the first glance one cannot say whether absolute fixation takes place or not. A very simple examination suffices to determine these doubts:--Cause the patient to gaze at a certain point on the horizon and cover first one eye and then the other. If the covered eye remains stationary, no squint exists, but if it is observed that when giving one eye its freedom and covering the other, the first must make a movement in order to fix the object to be looked at, it is only a question of discovering whether the squint does not simply ensue from the covering up of the eye. We will return to these cases at greater length, in order to occupy ourselves now with the fact, that the examination above referred to proves the non-existence of strabismus, while appearance still allows us to suspect its existence.

This apparent contradiction finds its explanation in the fact that the scientific notion of squinting is determined by the direction of the visual axes. Strabismus is present when one eye only is directed to the fixed point, while the visual line of the other eye deviates from it.

But we cannot see the direction of the visual line, we can only judge of it from the position of the cornea. It is exactly that line which joins the point fixed with the centre of the fovea centralis. We can determine the position of the cornea by a perpendicular line passing through the centre of the cornea; this does not coincide with the visual line but deviates from it about 5° outwards. In the case of parallel lines of vision the corneæ are directed slightly outwards, a position which we are accustomed to consider as the normal one. If the angle formed by the above-mentioned perpendicular and the visual line is larger than usual, i. e. if the corneæ move further outwards than usual, the unusual appearance strikes us, and gives us the impression of a divergent squint. The enlargement of this angle, which is usually indicated as Angle a, is a peculiarity of the hypermetropic eye; and where we have an apparent divergent squint we may expect to find also hypermetropia, while an apparent convergent squint occurs occasionally in myopia of high degree.

If we turn now to those cases in which a real deviation of the visual line occurs, we must first consider the cause, and afterwards distinguish it from paralysis of the ocular muscles. The faulty position may be constantly present or it may only occur when the paralysed muscle is called into action. It is almost invariably combined with double vision; sometimes the latter is the prevailing symptom, whilst the faulty position of the eye is in no way obtrusive, and can only be proved by careful investigation.

In contrast to paralysis of the ocular muscles stands the typical concomitant squint, in which the squinting eye normally accompanies the movements of the other. Transitional forms may thus be brought about, in some of which the paralysis recovers, with complete or almost complete restoration of movement, but with continuance of the squint. On the other hand, in concomitant strabismus, restriction of movement towards the opposite side not unfrequently develops itself.

This impairment of movement has its origin generally in a want of use. Those who squint have less need for movement, since one of their eyes is already directed obliquely. In divergent strabismus this is apparent, but in convergent strabismus the squinting eye governs the field of vision on the side to which it turns. When the fixing eye is turned towards the side of the squinting eye in convergent strabismus, the latter, it is true, makes a concomitant movement, which does not, however, bring it by a long way to the limit of the movement of which it is capable. The defect of motion is therefore generally present in both eyes, and is usually most marked in the squinting eye. Often, indeed, there is present at the same time a congenital or acquired insufficiency of the antagonistic muscle, but that want of use has also much to do with it, is shown by the improvement of mobility that often follows even short practice.

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