Impact of ageing on progressive thinning of the retinal nerve fibre layer in glaucoma

Background/aims To determine the proportion of progressive retinal nerve fibre layer thickness (RNFLT) change that can be attributed to normal ageing. Methods This prospective, longitudinal, cohort study included one eye each of 200 patients treated for open-angle glaucoma and 73 healthy control subjects who were followed with optical coherence tomography (OCT) every 6 months. A linear mixed-effects (LME) model was used to estimate the mean RNFLT slope and the difference between the two groups to evaluate factors affecting the slope, while adjusting for other variables. Results The median (IQR) age and follow-up of all participants was 68.3 (61.8 to 74.7) years and 10.1 (6.4 to 12.9) years, respectively. The median baseline mean deviation in patients with glaucoma was −3.79 (−6.84 to −1.57) dB. Among those classified within normal limits for baseline RNFLT (39 (19.5%) patients with glaucoma and 68 (93.2%) healthy subjects), the individual RNFLT slopes were significantly steeper in patients with glaucoma (median, −0.76 (–1.13 to −0.49) µm/year) compared with healthy subjects (−0.51 (–0.72 to −0.19) µm/year, p<0.01). The LME model showed a statistically significant negative RNFLT slope in healthy subjects (−0.54 µm/year, p<0.01). After adjusting for covariates, diagnosis of glaucoma contributed an additional −0.47 µm/year (p<0.01). Baseline global RNFLT had a slightly negative impact on RNFLT slope (−0.01/year, p<0.01), while baseline age had a significant positive effect (0.01 μm/year 2 , p<0.01). Conclusions Normal ageing contributed around one half of RNFLT thinning observed in patients treated for glaucoma.