Relationship of the Optical Coherence Tomography Signal to Underlying Retinal Histology in the Tree Shrew (Tupaia belangeri)

Abstract

To interpret the retinal origin of the optical coherence tomography (OCT) signal by objectively (i.e., minimal investigator bias) aligning in vivo OCT longitudinal reflectivity profiles (LRPs) with corresponding vertical histologic sections. The Zeiss StratusOCT system was used to obtain retinal B-scans in vivo in eyes from adult tree shrews. Subsequently, the retinas were fixed and embedded. Semithin vertical sections through the retina were obtained from the same locations as the LRPs. A statistical correlation procedure that accounted for axial tissue shrinkage determined the best relationship between features in the LRP and sublaminae boundaries in corresponding histology sections. For the optimal relationship, the three regions of high reflectivity in the inner OCT signal corresponded to (1) the nerve fiber and ganglion cell layers, (2) the inner plexiform layer and amacrine cell somas, and (3) the outer plexiform layer. The two regions of low reflectivity in the inner OCT signal corresponded to (1) the somas of Müller, bipolar, and horizontal cells in the inner nuclear layer and (2) the outer nuclear layer. The outer OCT signal had a region of high reflectivity that corresponded to the photoreceptor inner and outer segments, the pigment epithelium, Bruch's membrane, and at least part of the choriocapillaris. These results provide a clear interpretation for the OCT signal in terms of the underlying retinal anatomy. This interpretation can be used in vivo to identify sublaminae affected by retinal disease and has implications for the origin of the inner OCT signal in human retina.