Position of the incisions. Corneal incisions are to be avoided, if possible, for the following reasons: firstly, the cornea being free from blood-vessels heals comparatively slowly; secondly, the wound is liable to become fistulous owing to the rapidity with which the epithelium grows down the side of the wound. On the other hand, incisions situated from 3 to 6 millimetres behind the limbus are liable to injure the ciliary body, and, in addition to irido-cyclitis being set up by the trauma, the iris or ciliary body will prolapse into the wound and prevent the union of its edges, with the result that sepsis may spread into the globe along the prolapsed portion of the uveal tract and set up an irido-cyclitis which may not only ruin the eye affected but may also cause a sympathetic irido-cyclitis in the other eye (Fig. 79).
Fig. 79. Sympathetic Ophthalmia. The exciting eye of a case following cataract extraction. The section shows the incarceration of the iris in the wound.
The site of election of an incision into the anterior part of the globe is therefore about 1 millimetre behind the limbus; that is to say, as near the cornea as is consistent with obtaining a good conjunctival flap to cover the wound in the globe (Fig. 78). When possible it is advisable to make all incisions in an upward direction for the following reasons: They are more easily performed; any deformities, such as an iridectomy, are hidden by the upper lid; more perfect rest is obtained, as the wound is not exposed in the palpebral aperture, the eye being turned upwards when the lids are closed.
Fig. 80. Cystoid Scar after Glaucoma Iridectomy.
The immediate danger of the passage of a knife into the anterior chamber of the eye is the wounding of the lens. To avoid this the point of the knife should be always kept superficial to the iris if a clear lens be present in the eye. After operation the chief danger is prolapse of the iris into the wound. This is best avoided at the time of operation by carefully replacing the iris with the spatula at the end of the operation, but unfortunately prolapse not infrequently occurs during the first few days owing to the reaccumulation of the aqueous in the anterior chamber and its sudden escape through the imperfectly healed wound as the result of straining or of some movement on the part of the patient; the iris may be carried into the wound with the escaping aqueous, and a fistulous opening or a scar may form subsequently (Fig. 80).
The less manipulation used consistent with the object of the operation the less likelihood is there of cyclitis following it. All instruments should be held lightly in the fingers, which should be as far as possible responsible for the fine manipulation required. The part of the hand not actually holding the instrument should be steadied on the face before the instrument is brought in contact with the eye.
When more than one operation has to be performed on the same eye it is desirable that all ciliary injection after the first operation should have disappeared before the second is undertaken.