[Differences in anterior segment structure between Chinese Han people and American Caucasians]

Objective: To compare the difference of anterior segment structure between Chinese Han people and American Caucasians, and to explore the confounding factors of anterior chamber angle. Methods: Cross-sectional study. The study was designed to include two healthy groups of Chinese Han people (enrolled from Department of Ophthalmology, Peking University Third Hospital) and American Caucasians (enrolled from Department of Ophthalmology, University of California, San Francisco) from May 2008 to December 2010, each with approximately 120 participants, including 15 persons of each gender in each decade between 40 and 80 years of age. The parameters of the anterior segment were measured by the automatic refractive test, A-ultrasound and ultrasound biomicroscopy. Differences between the two groups were compared with the independent-sample t test or Wilcoxon two-sample test for continuous variable data and the χ(2) test for classified variable data. Multiple linear regression models were performed to analyze the associated factors of anterior chamber angle. Results: There were 118 subjects (118 eyes) and 117 subjects (117 eyes) enrolled in the Chinese and American Caucasians groups, respectively. Compared to Caucasians, Chinese had smaller A-ultrasound measured anterior chamber depth [(3.03±0.34) mm vs. (3.38±0.36) mm, t=-5.791, P<0.001], smaller relative lens position [0.227 (0.198, 0.256) vs. 0.235 (0.191, 0.262), Z=-3.063, P=0.002], smaller axial length [23.3 (20.9,28.3) mm vs. 24.2 (20.8,28.5) mm, Z=-5.510, P<0.001], smaller iris root distance [0.111 (0.000, 0.401) mm vs. 0.142 (0.000, 0.451) mm, Z=-3.188, P=0.001], smaller ciliary body thickness at 1 mm posterior to the scleral spur [0.661 (0.424, 0.892) mm vs. 0.716 (0.467, 0.942) mm, Z=-3.456, P=0.001], smaller trabecular ciliary process distance [0.780 (0.410, 1.400) mm vs. 0.930 (0.420, 1.470) mm, Z=-3.191, P=0.001], smaller trabecular ciliary process angle [73.4° (36.3°, 115.3°) vs. 81.1° (47.9°, 147.9°), Z=-3.407, P=0.001], smaller angle opening distance at 500 μm (AOD500) [0.181 (0.000, 0.703) mm vs. 0.264 (0.000, 0.806) mm, Z=-3.444, P=0.001], smaller angle recess area (ARA) [0.118 (0.011, 0.457) mm(2) vs. 0.179 (0.000, 0.626) mm(2), Z=-3.814, P<0.001], larger spherical equivalent [0.40 (-5.80, 4.00) D vs. -0.70 (-8.00, 4.00) D, Z=-5.454, P<0.001], larger lens thickness [(4.62±0.40) mm vs. (4.52±0.40) mm, t=2.077, P=0.039] and larger iris thickness [0.430 (0.280, 0.600) mm vs. 0.410 (0.240, 0.580) mm, Z=-2.263, P=0.024]. On average, with each decade of the increased age, Chinese had a greater decrease in the AOD500 than Caucasians (0.040 mm in Chinese vs. 0.030 mm in Caucasians), while the angle recess area decreased at the same rate (0.020 mm(2) in both groups). After adjusted for age, gender, spherical equivalent, axial length and other parameters of the anterior segment, the trabecular ciliary process angle [for AOD500, standardized regression coefficient (SRC)=0.487, R(2)=0.549, P<0.001; for ARA, SRC=0.372, R(2)=0.502, P<0.001] and anterior chamber depth (for AOD500, SRC=0.413, R(2)=0.476, P<0.001; for ARA, SRC=0.331, R(2)=0.403, P<0.001) were the main factors of anterior chamber angle parameters for Chinese and Caucasians, respectively. Conclusions: Compared with age and gender matched American Caucasians, Chinese Han people have more crowded anterior chambers and narrower anterior chamber angles. The more anteriorly positioned ciliary processes and shallower anterior chambers are the main factors that contributed to more crowded anterior chambers in Chinese Han people and American Caucasians, respectively. (Chin J Ophthalmol, 2018, 54: 820-826).