Visible-light optical coherence tomography fibergram for monitoring retinal ganglion cell axon bundles in vivo

Abstract

Purpose : Retinal neuropathies, such as glaucoma, are characterized by loss of retinal ganglion cells (RGCs), which leads to vision impairment and blindness. Extensive evidence has shown that as RGCs degenerate, their axon bundles deteriorate before the soma. We developed the visible-light optical coherence tomography (vis-OCT) fibergram to monitor the RGC axon bundles and their surrounding vasculature in vivo. Additionally, we implemented a novel analysis technique to quantify the organization of RGC axon bundles.

Methods : We imaged 2-4-month-old wild-type C57BL/6 mice using a commercially available vis-OCT system (Opticent Health, Evanston, IL, USA). We acquired four OCT angiography (OCTA) volumes from each eye with the optic nerve head positioned in different corners within their respective field-of-view. Each image volume consisted of 512 A-lines and 512 B-scans with each B-scan repeated five times. OCT structural datasets were reconstructed with each B-scan averaged five times and OCTA signal was extracted from split-spectrum phase variance. Threshold-based surface segmentation was used to segment the retinal nerve fiber layer from the structural OCT datasets and the superior and deep capillary plexuses from the OCTA datasets. Enface images were generated from the segmented datasets and overlaid to produce the final vis-OCT fibergram image shown in Figure 1. As a control, we compared the vis-OCT fibergram images with confocal images of flat-mounted retinas immunolabeled with Tuj1 to indicate RGC axon bundles. The organization of the RGC axon bundles was described for the first time using semi-log Sholl analysis.

Results : Vis-OCT fibergram images revealed the same RGC axon bundle structures as the confocal images. The Sholl regression term was 3.4 ± 0.7 mm^-1 for confocal images and 3.6 ± 1.1 mm^-1 for vis-OCT images (n=5). There was no statistical difference between the Sholl regression terms (p>0.05).

Conclusions : These results demonstrate the utility of the vis-OCT fibergram for monitoring RGC axon bundles in vivo. Further, our novel analysis technique provides a potential biomarker for tracking the degeneration of RGC axon bundles in patients with retinal neuropathies.

This is a 2020 ARVO Annual Meeting abstract.