Operation. The operation is usually performed under cocaine.
First step. The eye is fixed by grasping the conjunctiva directly opposite the spot at which the incision is to be made. The incision is then made by means of a keratome or bent broad needle directly behind the limbus, and enlarged laterally if desired (Fig. 107).
| Fig. 107. Optical Iridectomy. The incision being made with a keratome. | Fig. 108. Optical Iridectomy. Method of removing the iris to produce a small coloboma. |
Second step. A Tyrrell’s hook, bent at the correct angle, is passed on the flat into the anterior chamber. When the margin of the iris is reached the handle is rotated and the hook is made to engage the free border of the iris, which is then withdrawn from the wound; a small portion is removed with scissors, which should be held at right angles to the wound when dividing the iris (Fig. 108).
Third step. The iris should be carefully replaced and the pupil kept under the influence of eserine until the anterior chamber has re-formed, when atropine should be substituted.
Fig. 109. Optical Iridectomy. Showing the coloboma.
Care must be taken to see that the Tyrrell’s hook presents no sharp angle, and great care is required in its manipulation, otherwise the lens capsule may be damaged, and traumatic cataract will result. If the iris slips from the grasp of the Tyrrell’s hook, iris forceps should be used, the iris being grasped near its free margin and as small a portion as possible withdrawn.
Brudenell Carter’s method. The ordinary optical iridectomy divides the sphincter iridis and so inhibits the activity of the pupil. With the idea of obviating this, Brudenell Carter removed a small portion of the iris (button-hole), leaving the pupillary margin intact. On the whole the results of the latter operation are no more satisfactory, and the operation is more dangerous to perform owing to the likelihood of wounding the lens, and to the fact that monocular diplopia occasionally results.