Descriptive comparative morphology of the eye and ocular adnexa in Felidae: observations from a clouded leopard (Neofelis nebulosa), African lion (Panthera leo), and Pallas’s cat (Otocolobus manul)

The Felidae family includes diverse species with marked variation in ocular morphology. This study describes and qualitatively compares ocular morphology in a limited number of specimens: the clouded leopard (Neofelis nebulosa, n = 1), the African lion (Panthera leo, including two Angola lions, P. l. bleyenberghi, n = 2), and Pallas’s cat (Otocolobus manul, including O. m. manul, n = 1), whereas morphometric assessment of the orbital region was additionally based on skull material (clouded leopard, n = 1; Pallas’s cat, n = 2; lions, n = 11). Morphometric analyses were performed for the orbital region, eyeball, and selected accessory organs of the eye, using combined macroscopic and microscopic examinations. Histological staining included Mayer’s hematoxylin and eosin, Heidenhain’s Azan trichrome, Movat pentachrome, Masson-Goldner trichrome, Mallory’s trichrome with aniline blue, and Masson-Fontana, as well as histochemical staining with PAS, alcian blue (pH 1.0 and 2.5), alcian blue pH 2.5/PAS, and colloidal iron. Because of the very limited number of specimens, the study was strictly descriptive, and no statistical comparisons were performed. In the examined specimens, eyeball size generally corresponded to animal body size, whereas eyeball shape varied among individuals: the examined Angola lions had elliptical eyeballs, the examined clouded leopard had a nearly round eyeball, and the examined Pallas’s cat had a slightly elliptical eyeball. Corneal size and shape varied among the examined individuals. Histologically, the cornea consisted of four layers, Bowman’s layer was absent, and epithelial thickness varied among specimens. Palisades of Vogt were identified in the examined material. The tapetum lucidum varied in size among the examined animals and was most pronounced in the Angola lions; its coloration ranged from milky blue to blue-green. The anterior chamber depth appeared to correspond with eyeball size. Pupil shape also differed among the examined animals. Histological and histochemical analyses of the ocular adnexa revealed interindividual and intertaxon differences in microstructure; however, the very limited material did not allow broader interpretation. Orbital morphometric values generally followed overall skull size. Possible sex-related variation was observed in the lion material, but this requires verification in a larger series. The present study provides a descriptive anatomical and histological characterization of the eye and selected ocular adnexa in a small number of representatives of three felid taxa. These findings may serve as baseline reference data for comparative anatomy and veterinary ophthalmology, but they should not be interpreted as species-level patterns. Due to the limited sample size, these observations are preliminary and do not allow for species-level or population-level inferences. Because ante-mortem ophthalmic examinations were not available, subclinical ocular abnormalities cannot be excluded. In addition, because the material was collected post-mortem and subjected to fixation, processing, and sectioning, some morphometric values may have been affected by tissue distortion or shrinkage. Further studies based on larger series and standardized clinical evaluation are needed to verify the patterns observed in the present material.