Longitudinal analysis of retinal ganglion cell damage at individual axon bundle level in mice using visible-light optical coherence tomography fibergraphy

We developed a new analytic tool based on visible-light optical coherence tomography fibergraphy (vis-OCTF) to longitudinally track individual axon bundle transformation following 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 showed that axon bundles became wider and thicker at 3-days post ONC. The bundle swelling at 3-days post-ONC has correlated with about 15% retinal ganglion cell (RGC) soma loss. At 6-days post-ONC, axon bundles showed a significant reduction in lateral width and cross-sectional area, followed by a reduction in bundle height at 9-days post-ONC. Bundle shrinking at 9-days post-ONC has 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 the bundle width and height to indicate RGC soma loss. This study is the first to track and quantify individual RGC axon bundles in vivo following ONC injury and establish the correlation between the morphological changes of RGC axon bundles and RGC soma loss.