ANATOMY OF CORNEA
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is approximately 43 dioptres. While the cornea contributes most of the eye's focusing power, its focus is fixed. The curvature of the lens, on the other hand, can be adjusted to tune the focus depending upon the object's distance. Cornea has a diameter about 11.5mm and thickness about 0.5-0.6 in the center and 0.6-0.8 at the periphery. The cornea is one of the most sensitive tissues of the body. It is densely innervated with sensory nerve fibres via the ophthalmic division of the trigeminal nerve by way of 70–80 long ciliary nerves and short ciliary nerves. The ciliary nerves run under the endothelium and exit the eye through holes in the sclera apart from the optic nerve. A touch of the cornea causes an involuntary reflex to close the eyelid. The nerves enter the cornea via three levels; scleral, episcleral and conjunctival. Most of the bundles give rise by subdivision to a network in the stroma, from which fibres supply the different regions. The three networks are midstromal, subepithelial/Bowman's layer, and epithelium. The receptive fields of each nerve ending are very large, and may overlap. Cornea has no blood vessels because transparency is the most importance of the cornea. Cornea receive nutrients via diffusion from the tear fluid, aqueous humor and neurotrophins. Cornea gets oxygen directly from the air. The oxygen will dissolves in the tears and diffuses throughout the cornea.
The human cornea consist of 5 layers. From anterior to posterior the layers are corneal epithelium, Bowman’s layer, stroma, Descemet’s membrane and endothelium. Corneal epithelium is a thin epithelial multicellular tissue layer of fast-growing and easily-regenerated cells. It is...