Retinal Nerve Fiber Layer Rates of Change: Comparison of Two Optical Coherence Tomography Devices.

Purpose: To compare retinal nerve fiber layer (RNFL) thickness rates of change and their variability between two commercial optical coherence tomography (OCT) devices.

Design: Prospective cohort study.

Participants: Ninety-four glaucoma eyes (94 patients) with central damage or moderate to advanced glaucoma with ≥2 years of follow-up and ≥4 pairs of OCT scans.

Methods: A bivariate longitudinal Bayesian model was designed to compare inferences on RNFL rates of change from the two devices globally and in 12-clock-hour sectors. Optic nerve OCT scans were acquired with Spectralis and Cirrus OCT devices in the same session. We inspected longitudinal RNFL profile plots from both OCT devices for all subjects across all sectors and globally.

Main Outcome Measures: The rates of change, longitudinal variances, and proportions of significant negative and positive slopes (slope <0 or >0 μm/year and one-sided p<0.025, respectively) were compared between the devices.

Results: The mean (SD) baseline 24-2 VF mean deviation and median (range) follow-up time were -8.2 (5.5) dB and 4.5 (2.2-6.7) years, respectively. The mean (95% credible interval [CrI]) estimated global baseline RNFL thickness for Spectralis and Cirrus OCTs were 61.6 (58.9-64.1) and 65.3 (63.2-67.4) μm, respectively. The global RNFL rates of change for Spectralis and Cirrus OCTs were -0.70 μm/year (95% CrI = -0.88 to -0.51 μm/year) and -0.45 μm/y (95% CI = -0.63 to -0.27 μm/y) and were significantly faster for Spectralis compared to Cirrus OCT (difference =-3.85 μm, 95% CrI -5.28 to -2.42, p<0.001) as were sectoral rates in 5 out of 12 sectors. Higher proportions of significant negative RNFL rates of change were found with Spectralis OCT globally and in clock hour sectors 2-6 and 8-10 (corresponding to nasal, inferonasal, inferotemporal, and temporal regions). The proportions of significant positive rates of changes were small (0-3%) across sectors and similar between the devices.

Conclusions: Spectralis OCT rates of RNFL change were faster compared to those from Cirrus OCT. Spectralis OCT detected a higher proportion of significant negative rates globally and in some sectors. OCT devices are not comparable regarding detection of change in eyes with central damage or moderate to advanced glaucoma.