_First step. The incision._ The position of the surgeon is as for cataract extraction. The eye is fixed by grasping the conjunctiva close to the limbus downwards and inwards. If the patient be under an anæsthetic, two pairs of fixation forceps should be used, one being held by an assistant. Occasionally in glaucoma the conjunctiva tears very easily, and in these cases scleral forceps are of use, or, if the knife be already in the eye, grasping the insertion of the superior or inferior rectus. The Graefe’s knife should be directed downwards and inwards towards the point of fixation, the point being passed through the sclerotic 1.5 mm. behind the limbus to the outer side. Directly the anterior chamber is entered, the handle is depressed towards the patient’s chin. The knife-point is kept superficial to the iris and is passed very slowly across the anterior chamber, close to its periphery until the position of the counter-puncture is reached. The counter-puncture should be situated about 1 mm. behind the limbus in a direct line with the original puncture. Care must be taken in making the counter-puncture that the knife-point does not slip back on the sclerotic and so emerge further back in the eye than is desired. The knife is then made to cut out upwards and a good conjunctival flap is obtained. The incision should be carried out slowly, so that the aqueous escapes gradually, as sudden reduction in the intra-ocular tension is liable to lead to intra-ocular hæmorrhage. [Illustration: FIG. 113. IRIDECTOMY FOR GLAUCOMA. Failure to relieve the tension owing to the iris not tearing off at its junction with the ciliary body, due to atrophy from prolonged contact with the cornea.] _Second step. The iridectomy._ The iris forceps are inserted closed into the anterior chamber, opened, and made to grasp the iris near the periphery (Fig. 114) towards the side of the wound on which the iris is first to be divided; then with a slight side-to-side movement of the forceps the iris is withdrawn from the wound until its peripheral attachment to the ciliary body, near where it is held by the forceps, is felt or seen to give way (irido-dialysis) (Fig. 115). The iris is then drawn a little further out from the wound, and one side of the dialysis is divided with the scissors as near the scleral wound as possible. The iris held in the forceps is then pulled over to the other angle of the wound, and as much of it as possible is pulled out and divided close to the scleral incision (Fig. 116). The angles of the incision are freed from iris by means of the spatula and the conjunctival flap is replaced in position. Both eyes are then bandaged.