Parapapillary Beta Zone and Gamma Zone in a Healthy Population: The Beijing Eye Study 2011.

Abstract

To assess prevalence and size of the parapapillary beta zone and gamma zone in a healthy population. Within the population-based Beijing Eye Study, individuals without retinal or optic nerve disease were selected. Using optical coherence tomography (OCT), we measured the parapapillary beta zone (defined by presence of Bruch's membrane and absence of RPE) and gamma zone (region between Bruch's membrane end and optic disc border). The study included 723 individuals (mean age: 59.5 ± 7.6 years; range: 50-90 years). The beta zone was detected in 525 eyes (72.6%; 95% confidence interval [CI]: 69.4, 75.9). A larger maximum width of the beta zone (mean: 253 ± 225 μm) was associated (multivariate analysis; regression coefficient r2: 0.36) with older age (P < 0.001; standardized regression coefficient beta: 0.28), thinner temporal parapapillary choroidal thickness (P < 0.001; beta: -0.21), longer axial length (P < 0.001; beta: 0.14), longer vertical Bruch's membrane opening (BMO) length (P < 0.001; beta: 0.32), shorter horizontal BMO length (P = 0.003; beta: -0.12), and more pronounced vertical optic disc rotation of (P < 0.001; beta: 0.15). The gamma zone was detected in 190 eyes (26.3 ± 1.6%; 95% CI: 23.1, 29.5). A larger maximal width of the gamma zone (mean: 86 ± 187 μm) was (r2: 0.49) associated with longer axial length (P < 0.001; beta: 0.46), thinner central corneal thickness (P < 0.001; beta: 0.10), thinner temporal parapapillary choroidal thickness (P < 0.001; beta: -0.11), longer vertical (P < 0.001; beta: 0.15), and horizontal (P = 0.02; beta: 0.08) BMO length, and more pronounced vertical rotation of optic disc (P < 0.001; beta: 0.32). As measured by OCT in this healthy adult Chinese population, the gamma zone was mainly associated with longer axial length but not with age, while the beta zone was correlated mainly with older age and also with axial length. Both zones were largest in the temporal parapapillary region and smallest in the nasal region.