GROSS, HISTOLOGICAL AND HISTOCHEMICAL STUDIES ON THE EYEBALL AND EXTRAOCULAR MUSCLES OF SLOTH BEAR (Melursus ursinus)
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Date
2018-07
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KARNATAKA VETERINARY, ANIMAL AND FISHERIES SCIENCES UNIVERSITY, BIDAR
Abstract
The present study was conducted on the gross, histological and histochemical
studies on the eyeball, extraocular muscles and bony orbit of sloth bear. The bony
orbit was oval in shape with incomplete bony rim and formed by six bones. The shape
of the eyeball was almost circular and lens was biconvex in shape. The color of the
iris was dark brown and pupil was circular. Choroid showed the presence of semicircular tapetum and its base was placed horizontally ventral to the optic papilla.
Extraocular muscles were seven in number, muscle dorsal oblique was longest. The
corneal epithelium showed the presence of naked nerve endings and iron pigments in
their cytoplasm. Histologically, the iris was made up of stroma, iridial muscles and a
posterior epithelium and granula iridica was round and found at the tip of the iris.
Tapetum was made up of rectangular shaped cells which were oriented in a brick-like
manner. Well distinct Bruch’s membrane was observed. The iron pigments were
appreciated in pigmented epithelium of retina and it was devoid of melanin pigments
in the area adjacent to tapetal layer of the choroid. In the outer nuclear layer, the
nuclei of rods were darkly stained and abundant in number, whereas, nuclei of cones
were lightly stained and were few in number. In the inner nuclear layer horizontal
cells were located adjacent to outer plexiform layer, bipolar cells were oriented
radially with centrally located large heterochromatic nucleus, Muller cells were
oriented radially, elongated and located in between bipolar cells. Amacrine cells were
located in the innermost aspect of the inner nuclear layer, and capillaries were also
observed in the inner nuclear, inner plexiform, ganglionic and nerve fiber layer
indicating holangiotic pattern of retina. The nerve fibers converge at the optic disc and
emerge as optic nerve and optic papilla was goblet shaped. Extraocular muscles were
skeletal in nature showing fast and slow twitch based on the granular and
homogenous muscle fibers histologically. Presence of intense PAS positive character
indicated EOMs are highly metabolically active and participate in aerobic
metabolism.