Fig. 8. Effect of iridectomy on the anterior chamber angle. The elimination of pupillary block allows aqueous to pass without resistance from the posterior to the anterior chamber (A), eliminating the gradient in pressure that is responsible for anterior bowing of the peripheral iris (B). When iridectomy is not followed by deepening of the peripheral anterior chamber, it is not likely that it will be effective in preventing primary angle-closure glaucoma. (Spaeth GL. Glaucoma surgery. In Spaeth GL (ed). Ophthalmic Surgery: Principles and Practice. Philadelphia: WB Saunders, 1990.)