Anthropomorphic differences between angle‐closure and open‐angle glaucoma: the Beijing Eye Study

Editor, Glaucoma has been estimated to affect about 66 million people worldwide, with Asians accounting for almost half the world's glaucoma population. All population-based studies from Asia agree that primary angle-closure glaucoma (PACG) compared with primary open-angle glaucoma (POAG) is considerably more frequent in Asian countries than in Western populations (Congdon et al. 1992; Jacob et al. 1998; Foster et al. 2000). The present study aimed to assess differences in anthropomorphic measures between both types of glaucoma. The Beijing Eye Study is a population-based study performed in 2001. It included 4439 of 5324 subjects invited to participate, all aged ≥ 40 years. The study has been described in detail previously (Xu et al. 2007). The study protocol was approved by the Medical Ethics Committee of Beijing Tongren Hospital and all participants gave informed consent, according to the Declaration of Helsinki. Glaucoma was defined by the glaucomatous appearance of the optic nerve head, as described in detail recently (Xu et al. 2007). In open-angle glaucoma, the anterior chamber angle was open and the anterior chamber depth normal as assessed by slit-lamp biomicroscopy and gonioscopy. In angle-closure glaucoma, the chamber angle was either occluded by ≥ 15 degrees or the peripheral anterior chamber depth was ≤ 25% of corneal thickness. Anterior chamber depth was categorised in four grades, ranging from 1 = peripheral chamber depth > 50% of corneal thickness and 4 = peripheral chamber depth ≤ 25% of corneal thickness. Glaucoma was detected in 220 eyes (prevalence rate per eye [mean ± standard error] 2.5 ± 0.2%; 95% confidence interval [CI] 2.17−2.84) of 136 subjects (3.1 ± 0.3%; 95% CI 2.58−3.62). Of the 136 glaucoma subjects with glaucomatous optic nerve damage, 97 (71%) were diagnosed with open-angle glaucoma, and 39 (29%) with angle-closure glaucoma. In univariate analysis, PACG compared with POAG was significantly associated with shorter body height, age, hyperopic refractive error, female gender, lower educational level, and a shallower anterior chamber (Table 1). The groups did not vary significantly in terms of body weight, body mass index, optic disc area, and rural versus urban region (Table 1). Multivariate analysis including all the parameters with significant associations in univariate analysis revealed that the only parameter to retain a significant difference between the two glaucoma groups was anterior chamber depth (p < 0.001; 95% CI 2.74−18.7). Age (p = 0.98; 95% CI 0.90−1.12), gender (p = 0.28), body height (p = 0.98), refractive error (p = 0.66) and level of education (p = 0.74) were no longer significantly associated with either of the two glaucoma groups. The results suggest that subjects with PACG tend to be elderly, female, hyperopic subjects with relatively short body height and lower levels of education. Thus, given the interdependencies of the parameters, the main parameter associated with PACG is a shallow anterior chamber; the other anthropomorphic parameters do not have major associations with PACG. The results of the present study agree with those of the Reykjavik Eye Study, in which body height positively correlated with axial length, and age correlated negatively and body height correlated positively with vitreous chamber depth (Eysteinsson et al. 2005). This study was supported by the Beijing Key Laboratory Fund and the Beijing Natural Science Foundation.