Posterior pupillary synechiae affect a proportion of eyes subjected to iridectomy with or without drainage operation because (1) aqueous humour bypasses the pupil; (2) traumatic iridocyclitis occurs; (3) there is immobility of the iris in the iridectomy sector; (4) in eyes with angle closure glaucoma closer apposition of the iris to the anterior lens capsule increases the tendency; (5) pilocarpine aggravates (4) both in angle closure glaucoma and open angle glaucoma and produces a small immobile pupil facilitating pupillary membrane formation (occlusio pupillae). Pilocarpine should be avoided if possible as medical treatment at any time after a drainage operation. A beta blocker is the drug of choice. To eliminate posterior synechiae over a fair number of degrees of pupil (say 30 degrees) sector iridectomy can be done.