Differences in Iris Thickness Parameters Between Chinese and Caucasians as a Potential Risk Factor for Angle Closure Glaucoma

Abstract

Purpose: : To compare iris thickness parameters between Chinese and Caucasian patients.

Methods: : Right eyes of 140 patients from an academic glaucoma clinic in San Francisco were studied in this retrospective, cross-sectional study. Anterior segment optical coherence tomography (AS-OCT) images (Visante OCT Zeiss Meditec, Inc., Dublin, CA) of the temporal and nasal anterior chamber angles were obtained in dark conditions and analyzed with the Zhongshan Angle Assessment Program (ZAAP, Guangzhou, China). The following variables were compared between Chinese and Caucasian eyes: temporal and nasal iris thickness at 750 µm from the scleral spur (tIT750 and nIT750); temporal and nasal iris thickness at 2000 µm from the scleral spur (tIT2000 and nIT2000); iris thickness at the thickest point temporally and nasally (tITCM and nITCM); and temporal and nasal iris area (tIAREA and nIAREA).

Results: : There were 75 Caucasian eyes (53.6%) and 65 Chinese eyes (46.4%). There was no difference between Caucasians and Chinese for mean age, visual acuity, intraocular pressure, cup to disc ratio, or pupil diameter (p>0.10). A greater proportion of Chinese patients had peripheral iridotomy (47.7% vs 26.7%, p=0.010) and Chinese patients had narrower anterior chamber angles nasally (mean temporal ARA: 255 µm² vs 296 µm², p=0.171; mean nasal ARA: 205 µm² vs 294 µm², p=0.001). All iris thickness parameters were greater in Chinese patients than Caucasian patients (p<0.05) with the exception of tIT750 (p=0.357) and tIAREA (p=0.055). When age, gender, ARA, spherical equivalent of refraction, pupil diameter, and presence of laser peripheral iridotomy were controlled for, ethnicity remained a significant predictor for all nasal iris parameters and tIT2000 (p<0.05).

Conclusions: : Previous literature suggests that thicker irides and decreased deflation of irides upon dilation are associated with primary angle closure glaucoma. Chinese patients in this study had thicker irides than Caucasian patients, a physiologic difference that may contribute to iris crowding and angle closure glaucoma.

Keywords: iris • imaging/image analysis: clinical • anterior segment