الفهرس 
Acknowledgements
VEGF immunohistochemical analysisOnly 14 pages are availabe for public view
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Abstract
The present study investigated the developmental stages of cornea and retina of the New Zealand white rabbit eyeball. It was carried out on 87 embryos and 12 rabbits. The collected samples which covered most of the prenatal developmental stages ranged from 10 to 30 day. In addition, rabbits were sacrificed on the first and second weeks as well as the first month of postnatal life. The main results which were obtained from this study could be summarized as follows:
I) Cornea
• The prenatal development of the rabbit cornea begins on the 12th day of gestation by appearance of mesenchymal tissue between the surface ectoderm and the lens vesicle. The corneal epithelium begins to differentiate from the surface ectoderm on the 13th day of gestation, and reaches its adult form, consisting of 5-7 cell rows, at age of 2 weeks after birth. Interestingly, telocytes could be observed within the corneal epithelium. The surface of the epithelium consists of dark and light cells prenatally while becomes composed of dark, light and intermediate cells postnatally.
• The secondary stroma develops on the 16th gestational day with differentiation of keratocytes. At 23rd day of gestation, the lamellae of collagenous fiber begin to appear at the posterior part of the stroma. On the 30th day of gestation, the corneal stroma consists of 2 parts; an anterior fibroareolar part and a posterior lamellated fibrous part. At one week of age postnatally, the stroma becomes entirely lamellated. At 2 weeks of age, the lamellae of collagenous fibers become highly organized and the stroma becomes avascular indicating the cornea has become transparent.
• The Bowman’s membrane appears on the 23rd gestational day and disappears on the 30th day indicating that the cornea of the adult rabbit has no Bowman’s membrane. At that time, the Descemet’s membrane appears and continues to thicken postnatally. The corneal endothelium appears on the 20th gestational day as double layer of flattened cells and becomes a single layer of cuboidal cells on the 30th day. Gaps between the endothelial cells appear as crater like structures. These gaps decrease after eye lids opening.
• By immunohistochemical studies, the VEGF expression increases through the developmental stages reaching its maximum at the first week after birth after which, it decreases in all layers of the cornea and becomes negative in the stroma.
II) Retina
• On the 10th day of gestation, the primordia of the retina could be observed in the form of optic cup composed of inner and outer layers. The pigmented layer of the retina is differentiated from the outer layer of the optic cup at the 11th day of gestation. Therefore, the retinal pigmented layer is differentiated earlier than the neural retina. Throughout pregnancy and after birth, no pigment granules could be seen in the cytoplasm of the retinal pigmented epithelium.
• The ganglionic cells are the first cells to differentiate in the neural retina on the 15th day of gestation. The nerve fiber layer is formed on the 16th gestational day and represented by the axons of the ganglionic cells. The ganglionic cell layer is established on the 20th gestational day. At the same age, the inner plexiform layer appears. The ganglionic cell layer becomes composed of single layer of ganglionic cells at one week of age.
• On the 23rd day of gestation, Muller, amacrine and cone cells could be observed. The bipolar cells could be observed on the 27th day. On the 30th day of gestation, the horizontal and rod cells could be observed.
• Major developmental events take place on the 30th day (end of gestation) these are; division of the neuroblastic cell layer into inner and outer nuclear layers, appearance of the outer plexiform layer, development of the outer limiting membrane and differentiation of horizontal and rod cells.
• The photoreceptor layer could be detected on the 30th day of gestation with differentiation of the inner segments of the photoreceptors. The outer segments of the photoreceptors could be observed at one week of age.
• All layers of the retina have been established at the end of the first week of age. Although the eyelids are opened at 2 weeks of age and the retina becomes functional, the retina continues its development by decreasing cellular rows of inner and outer nuclear layers, increasing thickness of the inner and outer plexiform layers and increasing the length of the outer segments of the photoreceptors.
• By immunohistochemical studies, the S100 protein is expressed by the Muller cells that locate in the inner nuclear layer and its radiating processes that traverse the retina from the outer to the inner limiting membranes. Concerning to Calretinin, it is labeled within the amacrine cells which occupy the inner nuclear layer and the displaced amacrine cells that locate in the ganglionic cell layer.