To preserve a good filtration bleb at 12:00 o'clock, ophthalmic surgeons usually change their routine of cataract extraction. Making the incision below or laterally is uncomfortable, and technical complications are more apt to occur. Placement of the incision through the bleb causes the bleb to seal down postoperatively. A purely corneal incision narrows the opening and is difficult to close watertight without a conjunctival flap. Any leaking of the wound postoperatively keeps the pressure low, and the filtration bleb disappears. The following procedure allows cataract extraction in the usual way with a well closed wound, supported by a good conjunctival flap.
A fornix-based conjunctival flap is dissected from the limbus on each side of the bleb and carefully dissected posteriorly around the bleb without entering it. If there is any doubt on the limit of the bleb, the rest of the conjunctiva can be elevated by a subconjunctival injection
KENNEDY JA. Cataract Extraction After Filtering Operation. Arch Ophthalmol. 1965;74(3):365-366. doi:10.1001/archopht.1965.00970040367015