To report a case of fibrin pupillary block diagnosed by ultrasonic biomicroscopy (UBM) and treated by argon-neodymium:YAG (Nd:YAG) laser in a patient with uveitis.

A 56-year-old man visited the hospital for decreasing visual acuity and a sudden onset of pain in the right eye. Best corrected visual acuity was 0.02 in the right eye and 1.0 in the left eye. Intraocular pressure (IOP) was 48 mm Hg in the right eye and 18 mm Hg in the left eye. Slit-lamp examination revealed diffuse corneal stromal edema with Descemet's folds and uniform shallowing of the anterior chamber, with 360 degrees of peripheral iridocorneal touch in the right eye. A fibrin membrane was present across the pupil. UBM showed a fibrin membrane across the pupil, uniform shallowing of the anterior chamber, and peripheral angle closure. The lens was displaced posteriorly. A sequential Nd:YAG laser membranectomy was performed that same day, with immediate deepening of the anterior chamber and normalization of the IOP.

UBM can play an invaluable role in the diagnosis of fibrin pupillary block by showing the presence of a fibrin pupillary membrane, accumulation of aqueous in the posterior chamber, and a clear separation between the iris and the lens. Nd:YAG laser membranectomy can be performed effectively in a fibrin pupillary block.