Clinical Investigations on Squint

by C. Schweigger

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
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

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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.