Comparison of Iris Insertion Classification Among American Caucasian and Ethnic Chinese Using Ultrasound Biomicroscopy

Purpose. To qualitatively classify and compare types of iris insertion among American Caucasians, American Chinese, and mainland Chinese. Methods. Prospective multicenter cross-sectional study. Sex- and age-matched Caucasian, American Chinese, and mainland Chinese cohorts were enrolled. Ultrasound biomicroscopy (UBM) images of the anterior chamber were acquired. Qualitative classification of iris insertion into basal, middle, and apical categories was performed. Proportions of each type of insertion were compared among racial groups. Multivariate logistic regression was carried out adjusting for potential confounders. Results. Data from 117, 129, and 112 subjects were available for American Caucasian, American Chinese, and mainland Chinese subjects, respectively. The most common type of iris insertion in the superior quadrant was basal insertion in both ethnic Chinese and Caucasians. In the inferior, nasal, and temporal quadrants, Chinese showed significantly higher proportions of nonbasal insertion (P 1/4 0.048, P < 0.0001, P < 0.0001, respectively). After adjusting for confounders, nonbasal insertion was significantly associated with Chinese ethnicity in nasal and temporal quadrants (nasal, OR: 3.1, temporal, OR: 4.8). Increasing proportions of nonbasal insertion were found with advancing age in both Chinese and Caucasians. Conclusions. Chinese have significantly higher proportions of nonbasal iris insertion in the nasal and temporal quadrants when compared with Caucasians, even after adjusting for ASOCT-measured anterior segment biometry and iris characteristics. Longitudinal studies in patients who have PAC/PACG are needed to fully elucidate the relationship between iris insertion and angle closure development.