Comparison of Ciliary Body Anatomy between American Caucasians and Ethnic Chinese Using Ultrasound Biomicroscopy

Purpose: To compare the ciliary body morphology between the Caucasians and Chinese, and to determine the associated anterior segment parameters. Methods: The study groups were comprised of four age-and gender-matched cohorts: American Caucasians, American Chinese, southern and northern mainland Chinese. Ultrasound biomicroscopy (UBM) was performed to assess the following measurements of the ciliary body: trabecular-ciliary process distance (TCPD), trabecular-ciliary process angle (TCA) and ciliary body thickness at 1mm posterior to the scleral spur (CBT1). A-scan ultrasonography was used to measure lens thickness (LT) and relative lens position (RLP), defined as (ACD + LT/2)/AL. Results: There were 109, 111, 115 and 117 subjects enrolled in the American Caucasian, American Chinese, and southern and northern mainland Chinese groups, respectively. Collectively, the Chinese had smaller TCPD (0.834 +/- 0.234 versus 0.940 +/- 0.236mm, p < 0.001) and TCA (75.1 +/- 17.9 versus 85.0 +/- 21.5, p < 0.001) than Caucasians. No difference was found between the three Chinese subgroups, therefore they were combined as one for the following analyses. After multiple linear regression analysis, adjusting for age, gender, spherical equivalent (SE) and axial length (AL), TCPD and TCA were positively associated with CBT1 and RLP, but negatively correlated with LT in the whole sample. The ethnic Chinese had significantly smaller CBT1 (SRC = -0.177, p < 0.001) and RLP (SRC = -0.254, p < 0.001) than that of Caucasians. Conclusions: Compared with the Caucasians, the Chinese had a thinner ciliary body and a more anteriorly positioned lens, which may contribute to more anteriorly positioned ciliary processes in this population. These findings might help to explain the higher prevalence of angle closure in the Chinese.