Schweigger on Squint Part 10

Periodic divergent squint is divided by no sharply defined limits from those cases in which only a preponderance of the externi exists without insufficiency of the interni. We frequently find very considerable degrees of facultative divergence as a casual symptom, without the occurrence of manifest divergence or the presence of asthenopic troubles. If this is accompanied by weakness of the interni, absolute divergence occurs on looking at near objects, sometimes for distance also and certainly if we suppress binocular fusion by covering one eye or render it difficult by colouring one visual field with a red gla.s.s.

In these cases the indications for the operation are given either by asthenopia, by troublesome double images or by the disfigurement inseparable from periodic squint; it will depend on the degree of the facultative divergence, whether we confine the tenotomy of the externus to one eye or whether we distribute it between both eyes.

Finally, it may be desirable to still say a few words as to the most favorable period for the operation. The comprehension of the defective sight often present in squint as caused by "non-use" has resulted in the preposterous advice that tenotomy should be carried out as early as possible. I can vouch for the fact that even the earliest tenotomy of the ocular muscles is of no avail against congenital amblyopia. I have repeatedly seen children on whom tenotomy had been performed in their first year, usually with bad cosmetic result but with continuance of defective sight of the squinting eye.

The final result of the operation is almost always very unsatisfactory when performed on children before their fourth year. I can show a number of good results in children on whom I operated between their fifth and sixth year; however, the more I considered the subject, the more it seemed to me advisable to raise the tests which must be imposed on the patients. With children it is not so much a question of determining the limit of age, but whether their intelligence is sufficiently developed to render a reliable examination possible. A sufficient knowledge of letters and the power of reading is necessary to an accurate trial of vision; the entire bearing of the children must permit of the ophthalmoscopic diagnosis of the weak condition and should raise no scruples as to wearing spectacles which may be necessary after the operation. Under any circ.u.mstances no harm is done by deferring the operation until these conditions are fulfilled; the interval may be filled up by practising the mobility of the eyes, which does more good than the customary strabismus spectacles or even tying up the eye. If we tie up the fixing eye, the squinting one is certainly put into fixation, but the other squints instead, and of course it is just the same with the plan, as childish as it is antiquated, of tying on a pierced walnut sh.e.l.l before each eye.

Strabismus spectacles, _i. e._ those with a leather band to go round the head, provided with leaden discs which cover one eye completely and leave only a side aperture for the other, of course only induce a transfer of the squint to the covered eye, together with practice of the eye in a lateral direction; but apart from their unsightly appearance they require a constant lateral direction of the eye, which is followed even after a short time by fatigue of the muscles employed and soon becomes unbearable. This is not the case if we cause the mobility to be practised alternately and towards both sides; here we must insist that the limits of the outward movement are really reached.

These exercises are at least rational and tend to increase the strength of the antagonist, on which we must depend so much in the operation and to diminish an insufficiency made worse by want of practice.

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