Determination of retinal nerve fibre layer (RNFL) and ganglion cell/inner plexiform layers progression rates using two optical coherence tomography systems - the PROGRESSA study.

IMPORTANCE Glaucoma progression rates may differ depending on the retinal structural parameters measured and between devices. BACKGROUND To compare retinal nerve fibre layer (RNFL) and ganglion cell/inner plexiform layers (GCL/IPL) progression rates using two spectral-domain optical coherence tomography (OCT) systems. DESIGN Prospective, university hospital setting. PARTICIPANTS Cross-sectional study: 100 eyes from 53 glaucoma suspects and early manifest glaucoma cases. Longitudinal study: subset of 61 eyes from 33 participants. METHODS Same day optic nerve and macular images were acquired using Cirrus and Spectralis systems from which RNFL and GCL/IPL thicknesses were calculated. Longitudinal analysis of RNFL and GCL/IPL progression rates was calculated from 6x6- monthly follow-up OCT scans. MAIN OUTCOME MEASURES RNFL and GCL/IPL thicknesses in matched superior, inferior, and global regions were compared by both systems cross-sectionally and longitudinally. RESULTS At baseline, no RNFL thicknesses differed between devices. Cirrus GCL/IPL regions were significantly thicker than Spectralis (p<0.001). RNFL and GCL/IPL global progression rates (μm/yr) had a mean (SD) of -1.28 (1.11) and 95% CI:[-1.48, -1.09], and -0.51 (0.58) and 95% CI:[-0.62, -0.41], respectively. Progression rates were similar across devices. RNFL loss (%) progressed significantly faster than GCL/IPL, in all regions (p≤0.004). CONCLUSION Despite baseline thickness differences, overall Cirrus and Spectralis provided similar rates of RNFL and GCL/IPL progression in early glaucoma and can be considered comparable, though not interchangeable, in clinical practice. Further analysis is needed to determine if RNFL progresses faster than GCL/IPL in glaucoma, and whether one precedes the other. This article is protected by copyright. All rights reserved.