RNFB Orientation Map with Visible Light OCT for Optic Neuropathy Detection

Abstract

Purpose : Imaging retinal nerve fiber bundles (RNFB) in humans typically requires polarization sensitive optical coherence tomography OCT) or adaptive optics. In this study we demonstrate the use of visible light OCT (vis-OCT) for generating human RNFB orientation maps.

Methods : We used a human vis-OCT system with a wavelength range from 510 nm to 610nm, providing an axial resolution of 1.3 µm, to image four healthy subjects and five optic neuropathy patients. We used a high-density (HD) or ultra-high-density (UHD) isotropic scanning pattern, consisting of 512 A-lines and 512 B-scans. The HD covered a region of 6x6 mm² and the UHD covered 3x3 mm², both centered on the fovea. From reconstructed OCT images, we performed automatic segmentation of the top and bottom boundaries of the retinal nerve fiber layer (RNFL) with manual correction on each B-scan. The mean intensity projection of the RNFL region, normalized by outer retina layer intensity, was then used to generate vis-OCT fiber bundle images (vis-OCTF). For generating RNFB orientation map, the gradient of these images was computed, and a median filter was applied to mitigate noise-related gradient variations, excluding blood vessels. On UHD images, individual fiber bundles were traced from the fovea towards the optic nerve head based on the orientation vector field.

Results : Our high-resolution vis-OCT system, with HD or UHD scanning pattern, enabled clear visualization of RNFB on reconstructed vis-OCTF images. The fiber orientation maps were successfully generated for all high-quality HD scan images. Preliminary examination of patient images revealed larger variations in RNFB orientations in diseased eyes. Additionally, on UHD images, the vector field resulted fiber bundle tracing is comparable to manual tracing results.

Conclusions : This study demonstrates the feasibility of investigating human RNFB using its hyperreflective nature on vis-OCT structural images without requiring additional alterations to vis-OCT systems. The observed larger variations in RNFB orientations in optic neuropathy patients suggest the potential use of RNFB features as early biomarkers for optic neuropathy diseases.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.

 

Figure 1. Examples of vis-OCTF from a healthy (a) and a diseased eye (c), and their corresponding RNFB orientation heatmap (b) and (d). (e) the vis-OCTF from UHD scan, with examples of individual fiber bundle traced automatically (blue) and manually (red).