Comparison of thickness, retardation and birefringence of retinal nerve fiber layer between early glaucoma and healthy controls using along-the-bundle analyses based on polarization-sensitive OCT

Abstract

Purpose : To trace the retinal nerve fiber (RNF) bundles (RNFBs) from the optic disc to their ends and to study the course of the RNF layer thickness (RNFL-T), the RNF layer retardation (RNFL-R) and the RNF layer birefringence (RNFL-BIR) along the RNFBs in healthy and early glaucoma eyes using polarization-sensitive optical coherence tomography (PS-OCT).

Methods : This is part of a prospective cross-sectional study where we used a prototype PS-OCT instrument to acquire stitched wide-field PS-OCT scans. Here we present the results of 24 early glaucoma (Age: 59.6 years) vs. 27 age-matched healthy eyes (Age: 61.5 years). The RNFL was segmented and corrected where necessary, and the RNFBs were automatically traced and manually checked for correctness. Tracing started at a circle of 3 mm radius centered on the optic disc (OD) both towards the OD and the periphery. This analysis focusses on a sample of 9 RNFB traces at 80 deg. (above the disc to fovea line), 60 deg., 40 deg., 20 deg., 0 deg., -20 deg., -40 deg., -60 deg. and -80 deg (fig.1). Mean values and slopes along the bundles of RNFL-T, RNFL-R and RNFL-BIR were compared between groups with t-tests for sections of 1mm length.

Results : The traces located temporal superior and inferior showed statistically significantly reduced RNFL-T and RNFL-R (over 2 to 6 mm, and reduced RNFL-BIR over 2 to 3 mm for glaucoma compared to healthy controls (fig. 2). The slopes of RNFL-T and RNFL-R were significantly less steep for glaucoma compared to healthy controls in the temporal superior and inferior regions. The slopes of RNFL-BIR did not show a consistent pattern.

Conclusions : Early glaucoma shows significantly reduced RNFL-T and RNFL-R along large parts of the RNFBs and also reduced RNFL-BIR in some regions. We also describe more negative slopes of RNFL-T and RNFL-R, but not of RNFL-BIR along the bundles for the healthy as compared to the glaucoma cases.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

En-face image of phase retardation of one subject with the 9 selected traces highlighted.

 

Comparison of group mean values along the trace for RNFL-T (a, b, c), RNFL-R (d, e, f) and RNFL-BIR (g, h, i) for traces at 60 deg (a, d, g), 0 deg (b, e, h) and -60 deg (c, f, i); blue = healthy, red = glaucoma. Significance of t-tests of mean values (* p<0.05, ** p<0.01, *** p<0.001), and of mean slopes (+, ++, +++ as above)