_First step._ The surgeon, standing facing the patient, enters the anterior chamber about 2 millimetres inwards from the limbus at the junction of the middle and lower third of the cornea with a Graefe’s knife, the cutting edge directed downwards. The knife is then made to penetrate the iris and underlying capsule, and to travel beneath this to a similar point on the other side, where it is made to come back again into the anterior chamber by again penetrating the iris, and finally out again through the cornea. The knife is then made to cut out in a downward direction. _Second step._ Iris forceps are inserted and the flap of iris and capsule is withdrawn and as much of it removed as possible. A more or less triangular opening usually results. =Ziegler’s operation.= =Instruments.= Ziegler’s knife needle, speculum, fixation forceps. The object of the operation is to cut a V-shaped flap in the iris and underlying capsule, folding the flap backwards on its base so as to form a triangular opening in the iris membrane to serve as a pupil. _First step._ The knife needle is entered at the corneo-sclerotic junction with the blade turned on the flat and is passed completely across the anterior chamber to within 3 mm. of the apparent iris periphery. The knife is then turned edge downwards, and carried 3 mm. to the left of the vertical plane (Fig. 104). [Illustration: FIG. 104. IRIDOTOMY BY ZIEGLER’S METHOD. Showing the shape of the knife and the position of the first puncture in the iris; the cutting is performed by a sawing movement.] _Second step._ The point is now allowed to rest on the iris membrane, and with a dart-like thrust the membrane is pierced. Then the knife is drawn gently up and down with a saw-like motion, without making much pressure on the tissue to be cut, until the incision has been carried through the iris tissue from the puncture in the membrane to just beneath the corneal puncture. This movement is made wholly in a line with the long axis of the knife, the shank passing to and fro through the corneal puncture, loss of the aqueous being avoided in the manipulation (Fig. 105). _Third step._ The pressure of the vitreous will now cause the edges of the incision to bulge open immediately into a long oval. The knife-blade is raised until it is above the iris membrane, and is then swung across the anterior chamber to a corresponding point on the right of the vertical plane. Owing to the disturbance in the relation of the parts made by the first cut, this point is somewhat displaced and the second puncture must be made 1 mm. further over.