GROSS AND HISTOMORPHOLOGICAL STUDY ON EYE BALL OF THE ADULT MARWARI GOAT (Capra hircus)
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Date
2014
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AAU, Anand
Abstract
The present study entitled “Gross And Histomorphological Study On Eye Ball Of The Adult Marwari Goat (Capra hircus)” was carried out on eye balls of the ten adult Marwari goats. Immediately after collection of eye balls, they were subjected for ocular ultrasonography, echobiometrical and biometrical observations. Then 8-10 mm long incision was given in the limbus and whole eye ball fixed in Davidson’s fixative for 24-30 hours. The section of the sclera, cornea, lens, choroid, ciliary body, iris, irido-corneal angle and retina were stained with H. & E., Masson’s trichome and Periodic Acid Schiff (PAS).
Ultrasonography of eye ball (sonoanatomy) revealed cornea as a thin hyperechoic layer which formed the anterior wall of the anterior chamber. The anterior chamber was distended with the anechoic aqueous humor. The ciliary body and iris were seen as echogenic linear structure which extended from the peripheral globe towards the lens. The corpora nigra or iridica granules were seen as an echogenic round
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structure on the anterior surface of the dorsal iris. The anterior lens capsule was appeared as a convex echogenic line which was separated from the concave echogenic line of the posterior lens capsule by the anechoic lens. The vitreal chamber was filled with anechoic fluid.
Echobiometrical observations of the eye ball were measured. The mean value of the anterior chamber depth, antero-posterior depth of the lens, vitreous chamber depth and antero-posterior axis of the globe were 0.27 ± 0.02 cm, 0.80 ± 0.01 cm, 1.14 ± 0.01 cm and 2.13 ± 0.01 cm, respectively.
The overall mean value of the weight of the right and left eye balls of adult Marwari goat was 10.062 ± 0.06 gm. The overall mean values of the antero-posterior axis, horizontal axis and vertical axis of the eyeballs of both sides were 25.21 ± 0.05 mm, 27.62 ± 0.18 mm and 26.89 ± 0.03 mm, respectively.
The cornea was elliptical in shape with a horizontal diameter greater than the vertical diameter. The overall mean values of the horizontal and vertical diameter of the cornea were 19.26 ± 0.03 mm and 14.81 ± 0.04 mm, respectively. The overall mean value of the thickness of the cornea was 0.852 ± 0.03 mm. It was 0.911 ± 0.04 mm at the center and 0.794 ± 0.02 at the periphery.
The transparent and avascular lens was biconvex with the degree of convexity more at posterior side than anterior side. The lens was completely enclosed within a very thin PAS positive capsule. Behind the anterior surface of the capsule there was a single layer of epithelial cell. The lens fibers constituted the main body of the lens. It was suspended by the zonular fibers which arise from the ciliary body and attached to the lens capsule at the lens equator. The mean values of the weight, A-P axis and diameter of the lens were 0.921 ± 0.02 gm, 10.056 ± 0.03 mm and 12.493 ± 0.16 mm, respectively.
The sclera begin at the periphery of the cornea and extended posteriorly up to the optic nerve. The sclera had three part from outside to inside: the episclera, sclera and lamina fusca. The thickness of sclera was found to be varied from region to region, it was thickest at optic disc and thinnest at equator.
The cornea was composed of five layers a) Anterior Epithelium, b) Subepithelial basement membrane, c) Corneal stroma/Substantia propria, d) Descemet’s Membrane and e) Endothelium. Anterior epithelium (stratified squamous non-keratinized) was the outermost layer of the cornea and was composed of 5 to 9 rows of epithelial cells. The mean value of the total thickness of the cornea was 716.39 ± 13.84 μm. At the periphery and center it was 702.54 ± 42.11 μm and 730.24 ± 43.54 μm, respectively. The mean values of the thickness of the epithelial layers, thickness of stroma, thickness of the Descemet’s membrane and thickness of endothelium of the cornea were 77.20 ± 1.45 μm, 626.74 ± 12.02 μm, 10.70 ± 0.33 μm and 2.08 ± 0.10 μm, respectively.
The richly vascularized choroid extended from the ciliary body to the optic nerve and present between sclera and retina. The choroid consisted of the four layer: 1) Suprachoroidea, 2) Blood vessels layer, 3) Tapetum fibrosum and 4) Choriocapillaris. The total thickness of the choroid varied from region to region and tend to thicken along the posterior pole, becoming thinner towards the equator. The mean value of the thickness of the choroid was 45.53 ± 2.05 μm at the anterior/ora ciliaris retinae whereas, at the equator, it was 37.30 ± 3.48 μm and at the posterior pole/optic disc it was 50.64 ± 2.99 μm. The thickness of tapetum fibrosum was varied from 13.20 to 33.77 μm with the average of 26.40 μm.
The ciliary body was the anterior continuation of the choroid and it joined anteriorly with the iris. It was made up of the two ring shaped components: the pars
plicata and pars plana. The pars plicata was the anterior most part of the ciliary body, comprised of ciliary process and the flat pars plana started from posterior termination of the ciliary process, and merged with anterior termination of the retina (ora ciliaris retinae). Both portion of the ciliary body consisted of the epithelium, stroma and smooth muscles.
Iris was extended from the ciliary body and cover the anterior surface of the lens, except for central opening i.e. pupil. It was mainly consisted of the stroma and the posterior epithelial lining. The stroma was comprised of the loose connective tissue with smooth muscles, blood vessels, melanocytes and fibroblasts.
The irido-corneal angle was the area, located at the periphery of the anterior chamber and formed by the junction of the corneoscleral tunic (Limbic zone), base of the iris and anterior ciliary body. The irido-corneal angle of the eye of the goat was large and triangular and it was comprised of the pectinate ligament, the ciliary cleft, the trabecular meshwork (uveal and corneoscleral) and the angular aqueous plexus.
The retina was the innermost layer of the tunic of the eye ball. Retina had two portion, one was sensory (pars optic retinae) and another one was nonsensory. Non sensory part of the retina was started from the ora ciliaris retinae and covers the ciliary body (pars ciliaris retinae) and iris (pars iridis retinae). The sensory part of the retina was composed of ten layer: (1) the retinal pigmented epithelium (2) layer of rods and cones (3) external limiting membrane (4) outer nuclear layer (5) outer plexiform layer (6) inner nuclear layer (7) inner plexiform layer (8) ganglion cell layer (9) nerve fibers layer (10) internal limiting membrane.
The retinal pigmented epithelium (RPE) was the outermost single layer of flat cells of the retina. The cells of the RPE were pigmented except the area where the tapetum fibrosum was present. The next layer was layer of rods and cone cells which
comprised of only outer part of the rods and cones i.e. outer and inner segment. Outer limiting membrane separated the layer of rods and cones from the outer nuclear layer. The outer nuclear layer was composed mainly of nuclei of rods and cones. The outer plexiform layer was a thin layer that separated the outer nuclear layer from the inner nuclear layer. The inner nuclear layer was comprised of the nuclei of the horizontal cells, bipolar cells, amacrine cells and Muller’s cells. The inner plexiform layer was comprised of the bipolar and amacrine cell axon and dendrites of the ganglion cells. The ganglion cell layer was the innermost cell layer of the retina. The nerve fiber layer formed by the axon of ganglion cell. The internal limiting membrane was the innermost layer of the retina.
Thickness of the retina was found to be varied from region to region, it was thickest at optic disc and tapering towards the ora ciliaris retinae. The mean values of the total retinal thickness at Anterior/Ora ciliaris retinae, at equator and at posterior/Optic disc were 113.24 ± 5.68 μm, 139.82 ± 7.49 μm and 213.03 ± 14.45 μm, respectively.
Retinal detachment and folding of retina were the artifacts which found in present study. Retina detached from the retinal pigment epithelium or from choroid. It may be due to processing of tissue during preparation of block and sectioning. In more than 70 % of the sample, we found that retina took convex appearance vitreally which were almost round and oval in shape.
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Keywords
veterinary science, veterinary anatomy, study