Abstract
Purpose :
To visualize retinal neuronal cells in vivo in rats using visible-light optical coherence tomography (vis-OCT).
Methods :
Retinal images of Brown Norway rats were acquired with a 1.7-µm axial resolution, 50 kHz sampling rate, fiber-based vis-OCT system centered at 560 nm. Volumetric raster scans consisting of 512×2×512 A-lines covering a 1×1 mm2 area were acquired. In each imaging session, 5 volumes were recorded, with eyes moisturized at 10-second intervals between sessions. A total of 22 imaging sessions (resulting in 110 volumes) were performed per animal, taking approximately a half hour to finish. Non-rigid registration was performed on en face images generated by maximum projection of the OCT angiography signal along the entire A-lines to correct lateral deformation. In the axial direction, the reconstructed A-lines at each lateral position were axially aligned using cross-correlation. All registered volumes were then merged and averaged, resulting in the averaged structural and angiographic volumes used for further analysis.
Results :
Retinal layers can be clearly differentiated by reflectance contrast in B-scans (Fig. 1A). The nerve fiber bundles appeared brightest. At least three laminar sublayers within the inner plexiform layer could be identified. By projecting the slab anterior to the inner limiting membrane, randomly oriented posterior vitreous fibers were revealed (Fig. 1B). The appearance of the nerve fiber bundles, which were supplied anteriorly by the microvasculature of the superficial vascular plexus, could be seen in the en face image (Fig. 1C). The retinal circulation organization could be illustrated by overlaying the three vascular plexuses (Fig. 1D) from OCT angiography. Ganglion cell somas (Fig. 1E) were also successfully observed by projecting the slab just beneath the nerve fiber slab, with diameters of approximately 14.5 µm ± 4.4 µm. The density of bipolar cells in the inner nuclear layer was estimated to be ~1100 cells/mm2 in a 0.43×0.43-mm region of interest (Fig. 1F). As the inner and outer retina were focused simultaneously, photoreceptor nuclei (Fig. 1 G) and the photoreceptor ellipsoid zone (Fig. 1H) could be seen by projection of the outer nuclear layer and ellipsoid zone slabs respectively.
Conclusions :
Vis-OCT can achieve cellular resolution. This allows quantification of the number, size, and density of neuronal cells in the rat retina.
This is a 2020 Imaging in the Eye Conference abstract.