Identification, prevention, and treatment of silicone oil pupillary block after an inferior iridectomy. We treated two patients in whom silicone oil pupillary block developed despite a patent inferior iridectomy. The clinical characteristics of this complication were a deep anterior chamber, specular reflexes from the iris surface, identification by biomicroscopy of aqueous trapped inferiorly in the vitreous cavity, and no convection currents in the anterior chamber. This complication may be prevented by early face-down positioning of the patient after the operation, and the avoidance of large, centrally located, inferior iridectomies. We recommend that the iridectomy be placed peripherally no larger than 2 mm and propose a new technique for breaking the silicone oil block, which was clearly successful in one of the patients. 