Morphological features of parapapillary beta zone and gamma zone in chronic primary angle-closure glaucoma

Purpose To investigate the morphological features of parapapillary beta zone and gamma zone and their associated factors in eyes with chronic primary angle-closure glaucoma (CACG). Methods The observational cross-sectional study included 65 CACG eyes and 65 non-myopic control eyes. On enhanced depth imaging of optical coherent tomography images, the area of parapapillary beta zone and gamma zone, and the peripapillary choroidal thickness at 6 sectors were measured. The optic disc ovality index and Bruch's membrane opening (BMO) shape were further calculated. Results Beta zone was present in 103 (79.2%) eyes and gamma zone in 29 (22.3%) eyes. Compared to control eyes, CACG was associated with larger parapapillary beta zone, female gender, and older age (P < 0.01). No significant difference was observed in axial length and peripapillary choroidal thickness between both groups (P > 0.05). In multivariate analysis, beta zone area was positively associated with older age and higher prevalence of CACG (P < 0.01), while a larger gamma zone area was associated with a smaller disc ovality index and a higher BMO ovality ratio (P < 0.01). The peripapillary choroidal thickness at six sectors was decreased with older age (P < 0.01). Conclusions In mainly non-myopic subjects with or without CACG, larger parapapillary beta zone was correlated with older age and presence of glaucoma, while a larger parapapillary gamma zone was correlated with disc ovality but not with glaucoma. Parapapillary beta zone and gamma zone may play different roles in physiological and glaucomatous changes around optic nerve head.