Along-the-bundle analysis of the retinal nerve fiber layer of glaucoma eyes compared to control as analyzed by plolarization-sensitive OCT

Abstract

Purpose : To trace the retinal nerve fiber bundles (RNFBs) and to study the (mostly) decay of parameters describing the retinal nerve fiber layer (RNFL) along the RNFBs in healthy and early glaucoma eyes using polarization-sensitive optical coherence tomography (PS-OCT).

Methods : In this prospective cross-sectional study we used a prototype PS-OCT instrument to acquire wide-field scans composed of 7 times 3 volume scans in 21 early glaucoma (age 64.5 ±9.5 years) vs. 45 healthy eyes (age 50.7 ±13.7 years). The RNFL was segmented and the RNFBs were traced, starting at a 3 mm radius circle centered on the optic disc (OD) with 2 deg. spacing both towards the OD and the periphery. We focus on a sample of 5 RNFB traces at 40° (above the disc to fovea line), 20°, 0°, 340°. and 320°. The mean values and slopes along the bundles of RNFL-thickness (RNFL-T), RNFL-retardation (RNFL-R), RNFL-T times inter-trace distance (RNFL-TD), i.e. the bundle cross-sectional area, and RNFL-R times distance (RNFL-RD) were determined and compared between groups with t-tests for sections of 0.5 mm length.

Results : Glaucoma eyes showed statistically significantly reduced RNFL-T and RNFL-R over 2 to 6 mm depending on trace label. The largest difference between groups was observed temporal inferior (320°), where the significant differences extended over 5 to 6 mm for all parameters. For the 320° trace at 3 mm from the OD the difference between groups regarding the slopes of RNFL-T, and RNFL-TD was 6.0 µm/mm and 53.2 µm²/mm (p <0.0005 and p<0.005) with the healthy eyes showing more negative slopes. The courses along the bundles are shown in fig. 1 and fig.2 for the mean parameter values and the mean slope values.

Conclusions : Early glaucoma shows significantly reduced RNFL-T and RNFL-R along large parts of the RNFBs. We find more negative slopes along the bundles for the healthy as compared to the glaucoma cases. The local slope of the parameters tested may contain information about the local number of remaining ganglion cells, which is to be confirmed in a future study.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.

 

Mean values along the trace for RNFL-T (µm), RNFL-R (10 x deg), RNFL-TD (µm²/10) and RNFL-RD (10 x deg. x µm) at a) 0°, b) 340°, c) 320°

 

Mean slopes of RNFL thickness (µm/mm), RNFL retardation (10 x deg/mm), RNFL thickness times distance (µm²/10 x mm) and RNFL retardation times distance 10 x deg. x µm/mm) at a) 0°, b) 340°, c) 320°