Visible light optical coherence tomography reveals age-related photoreceptor changes in the mouse

Abstract

Near-infrared Optical Coherence Tomography (OCT) can image bands of alternating reflectivity that delineate the major layers of the retina in living subjects. With the latest technical developments, visible light OCT has taken this capability even further, revealing fine sub-bands and strata within conventional NIR OCT bands. Here we performed visible light OCT study of the retina in a cross-section of mice with varying ages. C57BL/6J, BALB/cJ, and a selection of mutant mice and controls (aged 1.15-20 months) were imaged with 1.0 micrometer axial resolution visible light OCT while under isoflurane anesthesia. Retinal layers and sub-layers were analyzed through a combination of manual and automated segmentation procedures. In agreement with previous studies, we found a decrease in outer nuclear layer (ONL) thickness with age. In addition, we found age-related changes in two closely-associated visible light OCT features. First, a hyporeflective band at the outer edge of the ONL was found to thin with age. Second, a moderately reflective band inner to the ONL was found to thin with age. Histological correlations suggest that outer ONL reflectivity oscillations, or striations, arise from the nuclei being arranged into rows, and that the moderately reflective band inner to the ONL arises from rod spherules. The concomitant age-related thinning of these visible light OCT features, along with the ONL, strengthens these hypothesized associations. These observations also suggest that changes in the organization of the ONL accompany age-related thinning, and that photoreceptor loss can be studied at the level of the soma and at the synapse by visible light OCT in vivo.