Strabismus essentially consists in a contracted state of one or more of the muscles of the eye. This, as was before intimated, is commonly the internal rectus. The shortening, varying according to the extent of the squint, is always attended with a corresponding elongation of the opposite muscle, so that it gradually loses, either in whole or in part, its antagonising influence. How this affection is brought about, in the first instance, is still unknown, though it is probable that it depends upon some lesion of the nerves which supply the muscles of the eye, rather than upon any actual lesion of these fleshy bundles themselves. Be this as it may, when the resultant distortion is permanent, the affected muscle, from being constantly engaged in holding the eye in its unnatural position, acquires a corresponding degree of development, in accordance with a law of the animal economy that, in proportion as an organ is exercised, will be its size and strength. The more frequent occurrence of convergent strabismus is owing, doubtless, to the fact that the internal straight muscle is not only larger and stronger than the others, but that it is inserted much nearer the cornea, deriving thus two important mechanical advantages.
One of the most disagreeable effects of strabismus is the deformity to which it leads, rendering the individual an object of constant observation and ridicule. Were this confined to infancy and childhood, it would be of comparatively little consequence, but when we reflect that it continues through life, and that it is a source of incessant mortification, the influence which it exerts upon the temper and disposition of the sufferer must often be of the most unhappy kind. A still more serious effect, however, is the impairment of the vision of the affected eye, which, never entirely absent, sometimes amounts nearly to a total loss, from the insensibility of the retina, which is sometimes as complete as in confirmed amaurosis. In another series of cases the person is myopic, or sees objects only at a short distance. In some instances, again, there is double vision, or objects appear indistinct, and run as it were into each other, the image painted on the retina being confused and imperfect.
The distortion in question can be remedied only by a surgical operation, it having no tendency to a spontaneous cure. On the contrary, it generally manifests a disposition to increase, particularly in children of a nervous, excitable temperament. In fact, the very worst forms of squint I have ever witnessed were in persons of this description. The question then arises, at what age ought we to operate? My opinion decidedly is the sooner the better. Provided the child be in good health, and not under one year of age, I would not hesitate a moment to resort to the knife for its relief. And why should we? The operation itself is not particularly painful, and if it be done at an early period it will commonly be necessary to perform it only on one eye, whereas if it be postponed until the age of ten or twelve, as some have suggested, we shall not be able to effect a cure without dividing the corresponding muscle of the opposite side. Moreover, the sight in the meantime will become considerably impaired, the retina will lose its insensibility, and the individual be an object of ridicule and insult; all of which may thus be obviated. But it may be urged that a resort to the knife at this tender age will be both difficult and dangerous; difficult, because of the struggles of the little patient, and dangerous, because of the great susceptibility of the nervous system. In regard to the first of these points, it may be stated that the resistance, however great, may be easily enough surmounted by proper management; and, as it respects the latter, that it has been vastly overrated. Operations much more severe are frequently performed even at a much earlier period. I have seen the primitive carotid artery successfully tied in an infant of less than six months; and I have myself repeatedly operated, with similar results, for harelip, and that too in the very worst forms of that malformation. I do not, therefore, in these objections, see sufficient reason for deferring the division of the affected muscle.
The instruments which I employ for the operation, are two lid-holders, a double sharp-pointed hook for fixing the eye, a pair of dissecting forceps for pinching up the conjunctiva, and a scalpel or pair of scissors. The surgeon should also be provided with two or three small sponges and a basin of cold water.
The lid-holders (Fig. 1.) are each about six inches long, made of steel with an ivory handle, quite slender, and curved at the extremity, which is fashioned after the manner of a fenestrated speculum, and not more than a third of an inch in width. These instruments may be conveniently replaced by a common speculum and the fingers of an assistant: still, they are very useful, and I prefer them to any other contrivance. The hook for fixing the ball is double (Fig. 2.), resembling that contained in some of the older eye-cases. It ought not to exceed five inches in length, and should be provided with a movable slide, to allow of the proper separation of the branches, each of which, two lines in width, terminates in a short hook as delicate as the finest needle. The forceps need not be quite the ordinary size; and, as to the scissors, the common pocket-case pair will answer the purpose much better than a curved or more delicate instrument. The knife I rarely use. A curved director (Fig. 3.) is serviceable, as it enables the operator to judge of the extent of his incisions.
| Fig. 1. | Fig. 3. | Fig. 2. |
In performing the operation, the patient may be either in the semi-erect or reclining posture, with his head supported by an assistant, or properly elevated by pillows. I generally prefer the latter, as the eye is more manageable, and the patient less apt to faint than when sitting. The face should look towards the light, and the sound eye be covered with a bandage, to enable the patient the better to roll the other outwards. If the surgeon be ambidexter, it does not matter where he stands: but if he uses one hand more adroitly than the other, he should place himself on the right side when he wishes to operate on the left eye; and, conversely, on the left if he wants to operate on the right. Only two assistants are necessary; one of whom, standing at the head of the patient, elevates the upper lid, and fixes the eye by inserting the sharp hook into the sclerotic coat, about two lines behind the cornea: the branches of the instrument being separated one-fourth of an inch, and the interval between them accurately corresponding with the horizontal axis of the eye. This precaution is important, and should never be neglected, otherwise it will by no means be so easy to find the affected muscle. The points of the hook should be fairly implanted into the substance of the sclerotic tunic, but no more. If it be passed simply through the conjunctiva, it will be impossible to steady the eye, to say nothing of the danger of lacerating that membrane, and thus inflicting unnecessary pain upon the patient. On the other hand, if it be pushed through the fibrous coat, violent inflammation might be set up. The other assistant, placed on the side of the affected eye, depresses the lower lid, and hands the sponges to the operator. It is sometimes more convenient to let this assistant steady the eye.
Everything being thus arranged, the operator pinches up a small fold of the conjunctiva, just behind the hook, or, in other words, about three lines behind the cornea, and makes a vertical incision into it with the knife or scissors, as he may prefer. Relinquishing the forceps, the edges of the wound will at once retract, exposing thereby a surface from four to six lines in length by two or three in breadth. At this moment there is usually some degree of hemorrhage, amounting often to more than half a teaspoonful, especially if the incision has been made too far back near the semilunar valve, where the parts are always more vascular than further forward. To arrest this a small sponge, pressed out of cold water, should be repeatedly applied; or, if it prove
