Microstructure of β-zone parapapillary atrophy and rate of retinal nerve fiber layer thinning in primary open-angle glaucoma

Objective To investigate whether the rate of retinal nerve fiber layer (RNFL) thinning differs according to the microstructure of β-zone parapapillary atrophy (PPA) as evaluated by spectral-domain (SD) optical coherence tomography (OCT) in primary open-angle glaucoma (POAG). Design Prospective, observational, comparative study. Participants A total of 195 eyes with POAG that had been evaluated by serial SD-OCT RNFL thickness measurements for ≥2 years. Methods On the basis of the extent of Bruch's membrane (BM) within the β-zone PPA (area without retinal pigment epithelium [RPE]), as shown in the infrared fundus images, PPA was divided into PPA_+BM (PPA with intact BM) and PPA_-BM (PPA devoid of BM). Eyes were categorized into group A (having PPA_+BM only, n=64), group B (having both PPA_+BM and PPA_-BM, n=58), group C (having PPA _-BM only, n=32), and group D (without β-zone PPA, n=41). The rate of progressive OCT RNFL thinning was determined by linear regression and compared between groups. Factors influencing the rate of RNFL thinning were evaluated, including age, sex, follow-up duration, history of filtering surgery, baseline RNFL thickness, baseline intraocular pressure (IOP), mean IOP and IOP fluctuation during follow-up, PPA types, baseline PPA width, PPA width increase, axial length (AXL), central corneal thickness, and visual field mean deviation (MD). Main Outcome Measures Rate of thinning of OCT RNFL thicknesses over time. Results Patients in groups B and C were significantly younger and more myopic, and had a greater AXL, than those in groups A and D (all P < 0.001). The rate of global RNFL thinning was significantly faster in group A (-1.66±2.94 μm/year) than in the other groups (group B, -0.87±1.28 μm/year; group C, 0.20±1.86 μm/year; group D, -0.28±1.74 μm/year; P = 0.001). Multivariate regression showed a significant association of shorter follow-up period (P = 0.016), greater baseline global RNFL thickness (P = 0.035), type of β-zone PPA (group A, P = 0.023), and greater baseline PPA_+BM width (P = 0.034) with a faster rate of RNFL thinning. Conclusions The rate of RNFL thinning differed according to the microstructure of β-zone PPA. It was faster for eyes with β-zone PPA with intact BM than for eyes without β-zone PPA or with β-zone PPA devoid of BM.