Clinical Investigations on Squint

by C. Schweigger

A deviation of 5 to 6 mm. may usually be balanced by means of simple double tenotomy if the conjunctiva is considerably loosened behind the caruncle; not unfrequently, however, we must be careful to strengthen the result by means of the after-treatment. Commonly, during the first twenty-four hours, the result appears to be quite satisfactory, whilst on the second or third day troublesome convergence again sets in. By practice of the outward movement we then usually obtain at once a perceptible improvement of the position. Both eyes are repeatedly turned as far as possible to the right and left, by which means is obtained on the one hand, exercise of the external recti, on the other, increase of the effect of the tenotomy of the internal recti. I order these exercises to be begun on the day after the operation.

Besides this, however, in the relation between accommodation and convergence of the visual axes there is a very essential cause which is able to lessen the immediate effect of the operation. Persons who squint inwards, even if emmetropic, have the habit of combining accommodation for near objects with excessive convergence of the visual axes, thus the immediate effect of the operation is diminished as soon as they begin to use their eyes again. This happens, not by a lessening of the effect of the tenotomy, which could, indeed, only be increased by exertion of the internal recti, but in that sufficient time is not given for the external rectus to regain its normal elastic tension. Nothing is changed at first by the operation in the customary relation between accommodation and innervation of the internal recti—it is a question, then, of avoiding every exertion of the accommodation for some time, in order that no inducement for strong convergence should be given. I am accustomed, therefore, even in the case of emmetropes, to paralyse the accommodation by means of atropine twenty-four hours after the operation, and to remove the far-point by convex glasses to about 0·70 m.; the spectacles must, of course, be worn constantly, for only by that means can we be sure that they are always used for near objects. After a few weeks the spectacles are discontinued, first for distance, then for near objects also. This after-treatment is not necessary under all circumstances; but I have repeatedly assured myself that an originally sufficient result which perceptibly diminished after a few days, could by this means be restored and permanently maintained even in emmetropes.

In the case of hypermetropes, we more often meet with the same experience; in permanent convergent squint it is by no means necessary to neutralise the hypermetropia permanently after the operation, but it happens here more often than in emmetropia, that a perfectly good immediate effect is lost within the first week after the operation, and can be restored again by permanently wearing the correcting convex glasses. In such cases also, I am accustomed after a few months to discontinue the spectacles for distance as an experiment, while they are still used for working.

Simple tenotomy of both internal recti does not, as a rule, suffice for deviations of more than 7 mm.; therefore, even if both eyes possess good visual power, we must still decide on tenotomy of both internal recti together with advancement of the external rectus of the squinting eye, or anticipate repeated tenotomies of the internal recti, or seek to obtain the greatest possible effect by means of slight modification of the method of procedure.

Provided that the muscle was completely divided, and sufficiently loosened from the conjunctiva during the first operation, a repetition of the tenotomy can only aim at an increase of the effect if the elastic tension of the antagonist has improved in the meantime. I very rarely therefore carry out repeated tenotomies; it seems to me much more desirable to obtain a sufficient result at one operation whenever that is possible.

In some cases where there is a deviation of 7 to 9 mm., the effect of the tenotomy may be increased by inducing a strong divergence immediately after the tenotomy of the internal recti, which is maintained for 6 to 8 hours. For this a thread is passed through the conjunctiva at the outer edge of the cornea about 4 mm. above the horizontal meridian, and out again about 2 mm. below the horizontal meridian, then from below upwards in the same way, so that the conjunctiva is contained in a loop. The needle is then passed through the external canthus from the conjunctival surface and fastened by tying it over a roll of paper. This procedure is only to be recommended in exceptional cases; a greater effect on the internal recti is thus obtained, while with reference to the position the result depends on the elastic tension of the external rectus just as in simple tenotomy.

If the squinting eye has only an unavailable visual acuteness, a combination of tenotomy of the internal rectus with shortening of the external rectus is the best procedure. As a rule, simple tenotomy of the internal rectus of the squinting eye is of very little use in such cases, as the abducens, weakened by continual extension and wanting practice, places too slight an opposing power in the balance. The chief effect of the operation then devolves on the other solely available eye, which is not a desirable circumstance, and is also frequently insufficient. On the other hand, the combination of tenotomy of the internal rectus with advancement of the external rectus enables us successfully to change the opposing muscular tensions. As a rule, the operation may be confined to the squinting, weak-sighted eye, as that suffices to obtain a correction of 5 to 6 mm.

If the result is seen to be insufficient, it may be supplemented by tenotomy of the internal rectus of the other eye; in the case of deviations of more than 7 mm. it is advisable to divide the operation between the eyes in this way.

The suture has a special use in so-called artificial strabismus; that is, in those cases where convergent is converted into divergent squint through unskilful treatment, or where tenotomy of the abducens, performed on account of "insufficiency of the internal recti," is followed by convergent strabismus. I have not found confirmation of the fear expressed by Arlt, that the method proposed by me could be scarcely practicable if it is a case of the advancement of a muscle too far forward, and I have corrected a large number of such cases in other practices. It is seldom profitable to take up things in which others have been unsuccessful, but it bring its own reward in the case of artificial squint.

Periodic convergent squint offers a less certain ground for the operation. The change between normal position and a very considerable squint gives rise to the fear that an operation which would be able to remove the convergence might finally induce divergent strabismus. This fear is certainly not groundless, but at the same time it must be remembered that, with the exception perhaps of a few cases of clearly accommodative deviation, elastic preponderance of the internal recti or insufficiency of the external recti is generally the cause of periodic squint also. I have frequently, in periodic squint, performed double tenotomy of the internal recti with the slightest possible loosening of the conjunctiva. I have also attempted to confine the operation to the shortening of the external rectus without loosening the internal recti and with success, but not frequently enough to be able to deliver a certain opinion upon it.