Comparative analysis of OCT-defined parapapillary beta and gamma zones between primary open angle glaucoma and primary angle closure glaucoma

The ophthalmoscopic beta zone of parapapillary atrophy has recently been proposed to divide into a gamma zone and a (new) beta zone based on OCT imaging. The present study was undertaken to compare the microstructural characteristics of parapapillary gamma and beta zones and their influencing factors between primary open angle glaucoma (POAG) and primary angle closure glaucoma (PACG). Seventy-three PACG patients that had no evidence of an acute attack and 78 POAG patients were enrolled. Patients were matched by propensity scores for age and visual field mean defect (MD) value. The area and angular extent of both zones were measured. In multivariate analysis, a larger beta zone was correlated with older age, severe MD value and longer axial length. A larger gamma zone was correlated with longer axial length. Older age and severe MD value were correlated with the concentric shape of beta zone. Comparing the PACG and POAG groups that adjusted for age and MD value, gamma zone was larger and more prevalent in the POAG group, while beta zone showed no significant difference. Taken separately, MD value was associated with the area and shape of beta zone in the PACG group. Axial length was associated with the temporal shape of beta zone in the POAG group. These data indicated that OCT-defined parapapillary beta and gamma zones exhibited different characteristics in two types of glaucoma. Clinically, the size of parapapillary beta zone may serve as a better indicator of glaucoma severity in eyes with PACG than that in POAG.