Optical Coherence Tomography of the Corn Snake (Pantherophis guttatus) Eye: An Exploratory Study
The aim of this exploratory study was to capture images of the anterior and posterior segments of the corn snake eye using spectral-domain optical coherence tomography (OCT). Postmortem OCT scans were conducted on three euthanized corn snakes (Pantherophis guttatus), followed by a histological examination of their eyes. OCT findings were correlated with histology to identify anterior and posterior ocular structures, and to delineate retinal layers on OCT. Total retinal thickness (RT) was manually measured every 360 μm from the edge of the optic disc over a 3,600-μm distance in the dorsal and ventral quadrant of each snake. In the anterior segment of the eye, OCT imaging successfully identified the spectacle, cornea, iris, lens, and Schlemm’s canal. The posterior segment scans revealed a vestigial conus papillaris and retinal folds adjacent to the optic nerve head, which were confirmed by histology. The membrana vasculosa was distinguishable from the surrounding retina, and despite some limitations in image resolution, retinal layers were discernible. There was a positive correlation between the total RT and the distance from the optic disc (with the retina being thicker farther from the optic disc). Additionally, the total RT in the ventral quadrant was significantly lower than in the dorsal quadrant. OCT imaging effectively identified various anatomical features and retinal layers of the corn snake’s eye. To establish comprehensive OCT references for the posterior segment of the eye, further studies involving healthy, living snakes are needed.Abstract
Histological section (A) and OCT scanning (B) of the anterior segment of the eye in corn snake (Pantherophis guttatus). The two eyes do not belong to the same individual and are not at the same ecdysis stage; S: spectacle; C: cornea; SSS: subspectacle space; AP: anterior pad; L: lens; CS: Schlemm’s canal; CR: ciliary roll; Zf: zonule fibers; PS: peripheral scale. Tissues were stained using a hematoxylin eosin phloxin safran (HPS) protocol for histology.
Retinal layer segmentation of a 2-yr-old corn snake (Pantherophis guttatus) by histology (A) and the corresponding optical coherence tomography image (B) and its schematic representation (C). mv: membrana vasculosa, NFL: nerve fiber layer, GCL: ganglion cell layer, IPL: inner plexiform layer, INL: inner nuclear layer, OPL: outer plexiform layer, ONL: outer nuclear layer, PRL: photoreceptor layer, RPE: retinal pigment epithelium, CH: choroid. Tissues were stained using a hematoxylin eosin phloxin safran (HPS) protocol for histology.
Correlation between histological sections (A), (C); and OCT scanning (B), (D); centered on the optic nerve head in corn snake (Pantherophis guttatus). (A), (B): retinal sections of the left eye of Snake 1; (C), (D): retinal sections of the right eye of Snake 3; (E): measurements comparison between OCT and histology. Measurements were performed on each side of the conus papillaris (*) for every eye, and measurements conducted on histology were found significatively lower compared to OCT. Red lines delimit the photoreceptor layer. Tissues were stained using a hematoxylin eosin phloxin safran (HPS) protocol for histology.
Histological section of the ciliary area (A) and OCT scanning of the retina (B) in corn snakes (Pantherophis guttatus). The two images do not belong to the same individual. CR: ciliary roll; mv: membrana vasculosa; HV: hyaloid vessel; OV: orbicular vein; R: retina; Zf: zonule fibers. Tissues were stained using a hematoxylin eosin phloxin safran (HPS) protocol for histology.
OCT scanning of the retina in Corn Snake 3 (Pantherophis guttatus) centered on retinal folds distant from the papillary area. These folds are visible on both the infrared image of the eye fundus on the left and on the cross-sectional OCT scanning on the right (white arrows).
(A) Comparison of the total retinal thickness (RT) in the ventral and the dorsal retinal quadrants in corn snakes (Pantherophis guttatus). White plots indicate the mean total RT. (B) Evolution of the mean total RT with the distance to the optic disc, ventrally and dorsally. Note that the point at 0 μm is fictive.
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