Importance of normal aging in estimating the rate of glaucomatous neuroretinal rim and retinal nerve fiber layer loss

Purpose To describe longitudinal rates of change of neuroretinal parameters in patients with glaucoma and healthy controls, and to evaluate the influence of covariates. Design Prospective longitudinal study. Participants Treated patients with glaucoma (n = 192) and healthy controls (n = 37). Methods Global disc margin-based neuroretinal rim area (DMRA) was measured with confocal scanning laser tomography, while Bruch's membrane opening-minimum rim width (BMO-MRW), BMO area (BMOA), and peripapillary retinal nerve fiber layer thickness (RNFLT) were measured with optical coherence tomography at 6-month intervals. Individual rates of change were estimated with ordinary least-squares regression, and linear mixed effects modeling was used to estimate the average rate of change and differences between the groups, and to evaluate the effects of baseline measurement and baseline age on rates of change. Main Outcome Measures Rates of change for each parameter. Results Subjects were followed for a median (range) of 4 (2-6) years. The proportion of controls who had significant reduction of neuroretinal parameters was 35% for BMO-MRW, 31% for RNFLT, and 11% for DMRA. The corresponding figures for patients with glaucoma were not statistically different (42%, P = 0.45; 31%, P = 0.99; 14%, P = 0.99, respectively). Controls had a significant reduction of BMO-MRW (mean: -1.92 μm/year, P < 0.01) and RNFLT (mean: -0.44 μm/year, P = 0.01), but not DMRA (mean: -0.22×10^-2 mm²/year, P = 0.41). After adjusting for covariates, patients with glaucoma had faster, but not statistically different, rates of deterioration compared with controls, by -1.26 μm/year (P = 0.07) for BMO-MRW, -0.40 μm/year (P = 0.11) for RNFLT, and -0.38×10^-2 mm²/year (P = 0.23) for DMRA. Baseline BMO-MRW and RNFLT significantly influenced the respective rates of change, with higher baseline values relating to faster reductions. Older age at baseline was associated with a slower reduction in rates of BMO-MRW. Reductions in intraocular pressure were related to increases in BMO-MRW and DMRA. There was a tendency for BMOA to decrease over time (-0.38×10^-2 mm²/year; P = 0.04). Conclusions Age-related loss of neuroretinal parameters may explain a large proportion of the deterioration observed in treated patients with glaucoma and should be carefully considered in estimating rates of change.