Plateau iris syndrome: changes in angle opening associated with dark, light, and pilocarpine administration

Abstract

PURPOSE: To report changes in angle configuration associated with dark, light, and pilocarpine administration in plateau iris syndrome. METHOD: In 10 eyes of 10 patients with plateau iris syndrome and persistent narrow angles after patent peripheral Nd:YAG laser iridotomy, ultrasound biomicroscopy was used to image variations in angle opening, iris thickness, and trabecular-ciliary process distance. Measurements were taken in the dark, in full room light, and after administration of pilocarpine 2%. RESULTS: Average angle opening distance increased in the light compared with the dark (113 ± 34 μm vs 22 ± 34 μm, P = .0001) and increased further after pilocarpine administration (171 ± 52 μm vs 113 ± 34 μm, P = .0034). Average iris thickness decreased in the light compared with the dark (338 ± 34 μm vs 436 ± 58 μm, P = .0009) and decreased further after pilocarpine administration (253 ± 48 μm vs 338 ± 34 μm, P = .0002). Average trabecular meshwork–ciliary process distance measurements were smaller than normal and did not change significantly in the light compared with the dark (481 ± 42 μm vs 464 ± 44 μm, P = .4001) or after pilocarpine administration compared with light (451 ± 67 μm vs 481 ± 42 μm, P = .1304). CONCLUSIONS: In plateau iris syndrome, anteriorly located ciliary processes support the peripheral iris. Changes in angle opening in dark and light are solely related to changes in iris thickness. Pilocarpine produces iris thinning and is an effective method of opening the angle. Ultrasound biomicroscopy can be used to perform a darkroom provocative test, which provides information on whether the angle anatomically closes in the dark.