Ethnic difference of the anterior chamber area and volume and its association with angle width

Abstract

Purpose: To compare the anterior chamber area/volume (ACA/ACV) and their relationship with the drainage angle between adult Caucasians and Chinese.

Methods: Study groups were comprised of four age- and sex-matched cohorts: American Caucasians, American Chinese, southern mainland Chinese, and northern mainland Chinese. All subjects were consecutively recruited from general ophthalmology clinics except for southern mainland Chinese participants who were drawn from an ongoing population-based study. Anterior segment optical coherence tomography (ASOCT) images were obtained under dark conditions. Customized software was used to analyze structural indices including ACA/ACV, angle opening distance (AOD), anterior chamber depth (ACD), anterior chamber width (ACW), lens vault (LV), corneal arc depth (CAD), iris thickness (IT), iris curvature (ICurv), and iris area (IArea).

Results: Data from 121, 124, 121, and 120 participants were obtained of American Caucasians, American Chinese, and southern and northern mainland Chinese, respectively. After multiple linear regression analysis, adjusting for age, sex, pupil diameter (PD), and axial length (AL), ACA/ACV was positively associated with ACD, ACW, CAD, and corneal radius of curvature (CR) but negatively related with ICurv and IArea. Ethnic Chinese had significantly smaller ACA (β = -0.18, P = 0.022) and ACV (β = -3.9, P = 0.001) than Caucasians. ACV contributes the most to AOD variation for both Chinese (standardized regression coefficient [SRC] = 0.47, P < 0.001) and Caucasians (SRC = 0.59, P < 0.001).

Conclusions: Compared with Caucasians, ethnic Chinese had smaller ACA/ACV independent of ACD, ACW, ICurv, IArea, PD, CR, and AL. ACA/ACV is the most prominent contributor to angle width variation for both Chinese and Caucasians in this study.

Figure 1.

Schematic figure illustrating anterior segment biometric parameters measurement. Distance between LSS and RSS was defined as ACW. The perpendicular bisector of the ACW line intersected with corneal endothelium, anterior lens surface, and ACW line at points A, B, and C, respectively. The length of AB represents the anterior chamber depth, BC represents lens vault, and AC represents corneal arc depth. The gray area denotes ACA.

Figure 2.

Definition of angle- and iris-related parameters. Angle opening distance (AOD₅₀₀) is measured on a line perpendicular to the plane of the trabecular surface 500 μm anterior to the SS and extended to meet the surface of the iris (length of EF). The iris thickness was measured at 750 μm anterior to the SS (IT750) as the shortest distance between anterior and posterior iris surfaces (length of AB). ICurv was determined by creating a line from the most peripheral to the pupillary edge of the iris and then measuring the perpendicular distance from this line to the greatest convexity point along posterior iris surface (length of CD). IArea is the area within the iris contour bordered by a line through the SS and perpendicular to the meshwork line (gray area).