Comparison of factors associated with occludable angle between american Caucasians and ethnic Chinese

Abstract

Purpose: To determine if factors associated with gonioscopy-determined occludable angle among American Caucasians are similar to those found in ethnic Chinese.

Methods: This is a prospective cross-sectional study with 120 American Caucasian, 116 American Chinese, and 116 mainland Chinese subjects. All three groups were matched for sex and age (40-80 years). Gonioscopy was performed for each subject (occludable angles = posterior trabecular meshwork not visible for ≥2 quadrants). Anterior segment optical coherence tomography and customized software was used to measure anterior segment biometry and iris parameters, including anterior chamber depth/width (ACD, ACW), lens vault (LV), and iris thickness/area/curvature.

Results: In both Chinese and Caucasians, eyes with occludable angles had smaller ACD and ACW, and larger LV and iris curvature than eyes with open angles (all P < 0.005). Chinese eyes had smaller ACD and ACW than Caucasian eyes (both P < 0.01) in the occludable angle cohort. Iris characteristics did not differ significantly between Chinese and Caucasians in the occludable angle cohort. Based on multivariate logistic regression, gonioscopy-determined occludable angle was significantly associated with LV, iris area, and sex (all P < 0.03) in Chinese; and with LV, ACD, iris thickness, age, and sex (all P < 0.04) in Caucasians.

Conclusions: Several factors associated with occludable angle differed between Caucasians and Chinese, suggesting potentially different mechanisms in occludable angle development in the two racial groups. This is the first study to demonstrate that lens vault is an important anterior segment optical coherence tomography parameter in the screening for angle closure in Caucasians. In addition, iris thickness was a significant predictor for occludable angles in Caucasians but was not in ethnic Chinese.

Keywords: ASOCT; angle closure glaucoma; gonioscopy; multiethnicity; occludable angle.

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 ACD, BC represents LV.

Figure 2

Schematic figure illustrating iris parameters measurement. A 750-mm radius circle centering SS crosses the anterior iris surface at point A. The software will identify a point B along the posterior iris surface that locates closest to A. The distance between A and B is iris thickness at 750 mm (IT750). Iris curvature (Icurv) is determined by creating a line from the most peripheral to the pupillary end of the iris, and the perpendicular distance from this line to the most convex point along the posterior iris surface (point C to D) is defined as Icurv. Iris area (Iarea) is the cumulative area of the full length of iris, indicated by the gray area.