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Differences in Iris Thickness Among African Americans, Caucasian Americans, Hispanic Americans, Chinese Americans, and Filipino-Americans

Purpose:To evaluate the capability of iris thickness parameters to explain the difference in primary angle-closure glaucoma prevalence among the different racial groups. Methods:In this prospective study, 436 patients with open and narrow angles that met inclusion criteria were consecutively recruited from the UCSF general ophthalmology and glaucoma clinics to receive anterior segment optical coherence tomography imaging under standardized dark conditions. Images from 11 patients were removed due to poor visibility of the scleral spurs and the remaining images were analyzed using the Zhongshan Angle Assessment Program to assess the following measurements for the nasal and temporal angle of the anterior chamber: iris thickness at 750 and 2000 &mgr;m from the scleral spurs and the maximum iris thickness at middle one third of the iris. Iris thickness parameters were compared among and within the following 5 different racial groups: African Americans, Caucasian Americans, Hispanic Americans, Chinese Americans, and Filipino-Americans. Results:In comparing iris parameters among the open-angle racial groups, significant differences were found for nasal iris thickness at 750 and 2000 &mgr;m from the scleral spurs in which Chinese Americans displayed the highest mean value (P=0.01, P<0.0001). Among the narrow-angle racial groups, significant difference was found for nasal iris thickness at 2000 &mgr;m from the scleral in which Chinese Americans showed the highest mean value (P<0.0001). Significant difference was also found for temporal maximum iris thickness at middle one third of the iris in which African Americans exhibited the highest mean value (P=0.021). Iris thickness was modeled as a function of angle status using linear mixed-effects regression, adjusting for age, sex, pupil diameter, spherical equivalent, ethnicity, and the use of both eyes in patients. The iris thickness difference between the narrow-angle and open-angle groups was significant (P=0.0007). Conclusions:Racial groups that historically showed higher prevalence of primary angle-closure glaucoma possess thicker irides.