Longitudinal Analysis of Retinal Ganglion Cell Damage at Individual Axon Bundle Level in Mice Using Visible-Light Optical Coherence Tomography Fibergraphy.

Purpose: We developed a new analytic tool based on visible-light optical coherence tomography fibergraphy (vis-OCTF) to longitudinally track individual axon bundle transformation as a new in vivo biomarker for retinal ganglion cell (RGC) damage. Methods: After acute optic nerve crush injury (ONC) in mice, we analyzed four parameters: lateral bundle width, axial bundle height, cross-sectional area, and the shape of individual bundles. We next correlated the morphological changes in RGC axon bundles with RGC soma loss. Results: We showed that axon bundles became wider and taller at three days post ONC (pONC), which correlated with about 15% RGC soma loss. At six days pONC, axon bundles showed a significant reduction in lateral width and cross-sectional area, followed by a reduction in bundle height at nine days pONC. Bundle shrinking at nine days pONC correlated with about 68% RGC soma loss. Both experimental and simulated results suggested that the cross-sectional area of individual RGC axon bundles is more sensitive than bundle width and height to indicate RGC soma loss. Conclusions: This study is the first to track and quantify individual RGC axon bundles in vivo after ONC injury. Translational Relevance: Recognizing RGC loss at its earliest stage is crucial for disease diagnosis and treatment. However, current clinical methods to detect the functional and structural changes in the inner retina are not sensitive enough to directly assess RGC health. In this study, we developed vis-OCTF-based parameters to track RGC damage, making possible to establishing a quantifiable biomarker for glaucoma.