Purpose. To assess the anterior chamber drainage angle width in the dark and the dark-to-light change (Δ) between Caucasians and Chinese aged 40 years and older. Methods. The study groups comprised four age- and sex-matched cohorts: American Caucasians, American Chinese, southern mainland Chinese, and northern mainland Chinese. Anterior segment optical coherence tomography (ASOCT) images of the anterior chamber angles were obtained under both light and dark conditions. The parameters analyzed included angle opening distance (AOD), angle recess area (ARA), and trabecular-iris space area (TISA). Results. Data were obtained from 121, 124, 121, and 120 participants who were American Caucasians, American Chinese, and southern and northern mainland Chinese, respectively. In a multiple linear regression analysis, adjusted for age, sex, refractive status, pupil size, lens location, and anterior chamber depth (ACD) and width (ACW), the ethnic Chinese had significantly smaller ARAs (regression coefficient, β = -0.06, P < 0.001) and TISAs (β = -0.01, P = 0.039), as well as greater ΔAODs (β = 0.03, P = 0.009) and ΔTISAs (β = 0.02, P = 0.029) than did the Caucasians. For the dark-to-light change analysis, the independent associations between angle width and iris thickness (IT) and iris curvature (ICurv) were identified only in the Chinese. Conclusions. Compared with the Caucasians, the ethnic Chinese had smaller ARA and TISA, but greater dark-to-light changes in AOD and TISA, independent of refractive status and overall ocular anterior segment dimensions.
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