Longitudinal Observation of Retinal Response to Optic Nerve Transection in Rats Using Visible Light Optical Coherence Tomography

Abstract

Purpose To characterize rat retinal responses after optic nerve transection (ONT) by visible-light optical coherence tomography (vis-OCT). Methods Unilateral ONT was performed in Brown Norway rats (n = 8). In vivo, vis-OCT retinal imaging was performed on the experimental eyes before ONT (baseline), and two days, one week, two weeks, and four weeks (endpoint) after ONT, as well as on fellow eyes at the endpoint. The system was operated at a 70 kHz A-line sampling rate with both raster scans (512 × 2 × 512 A-lines), and circular scans (2048 × 100 A-lines) acquired around the optic disc. Retinal layers were segmented to calculate layer thicknesses and project en face images for visualization and quantifications. Vessel densities and oxygen saturation were used to evaluate the morphologic and functional impact on the retinal vasculature. Results After ONT, retinal nerve fiber bundles demonstrated significant degeneration, starting at two weeks, with a reduction of thicknesses quantified on the nerve fiber layer, ganglion cell complex, and total retina. Along with that, the activation of macrophage-like cells in the vitreoretinal interface was also observed. Vessel densities for all three retinal plexuses were unaffected over the period of observation. However, oxygen saturation in retinal arteries and veins was significantly reduced at four weeks after ONT. Conclusions Vis-OCT can provide high-definition, in vivo characterization of retinal responses to ONT in rats. Despite a significant reduction in retinal layer thickness, this was not accompanied by alterations in vascular density. Despite this, oximetry indicates reduced retinal oxygen saturation, suggesting that altered vascular physiology is not reflected in the anatomic appearance of retinal blood vessel density alone.

A deep learning network for parallel self-denoising and segmentation in visible light optical coherence tomography of human retina

“…The 3D imaging capability provides accurate vessel lumen segmentation that allows isolating signal within microvasculature to avoid other confounding signals as in other fundus-based oximetry. By that, microvascular retinal oximetry down to capillary level has been reported by VIS-OCT [11–13]. Clinical feasibility of microvascular sO 2 in parafoveal vessels that are around 20-30 μm in diameter have been demonstrated in several retinal vascular pathologies [14,15].…”