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Corneal corpuscles appearing fusiform in section; Lamellae, the fibers of which are cut longitudinally; Transition to the sclera, with more distinct fibrillation, and surmounted by a thicker epithelium; Small blood vessels cut across near the margin of the cornea
The corneal epithelium (epithelium corneae anterior layer) is made up of epithelial tissue and covers the front of the cornea. It acts as a barrier to protect the cornea, resisting the free flow of fluids from the tears, and prevents bacteria from entering the epithelium and corneal stroma.
Corneal ulcer – an inflammatory or infective condition of the cornea involving disruption of its epithelial layer with involvement of the corneal stroma. Corneal neovascularization – excessive ingrowth of blood vessels from the limbal vascular plexus into the cornea, caused by deprivation of oxygen from the air.
The corneal limbus is the border between the cornea and the sclera. [2] It is highly vascularized. [2] The corneal limbus' responsibilities include protection, healing, and controlling eye pressure. The limbus contains corneal stem cells that play key roles in corneal healing (renewing the corneal epithelium). [3]
Surface ectoderm forms the lens, corneal epithelium and eyelid. The extracellular mesenchyme forms the sclera, the corneal endothelium and stroma, blood vessels, muscles, and vitreous. The eye begins to develop as a pair of optic vesicles on each side of the forebrain at the end of the fourth week of pregnancy.
The outermost layer, known as the fibrous tunic, is composed of the cornea and sclera, which provide shape to the eye and support the deeper structures. The middle layer, known as the vascular tunic or uvea, consists of the choroid, ciliary body, pigmented epithelium and iris.
The middle (third in number; provided the first layer being the anterior and outermost and the sixth layer being the posterior and the inner most), thickest layer is also called the stroma. The sclera, like the cornea, contains a basal endothelium, above which there is the lamina fusca, containing a high count of pigment cells. [6]
It is composed of strong, randomly oriented collagen fibrils in which the smooth anterior surface faces the epithelial basement membrane and the posterior surface merges with the collagen lamellae of the corneal stroma proper. [1] In adult humans, Bowman's layer is 8-12 μm thick. [2] With ageing, this layer becomes thinner.