The clear covering of the eye is called the cornea. The cornea itself is composed of five distinct layers, which (from outside to inside) are the corneal epithelium, Bowman's membrane, Corneal stroma, Descemet's membrane, and the endothelium.
The cornea is a very interesting tissue in that it is avascular, meaning it lacks blood vessels. The cornea absorbs nutrients, including oxygen, from both the tear fluid and the aqueous humor, which is the liquid that fills the interior chamber of the eye.
In addition to protecting the eye by preventing the entry of foreign particles, the cornea acts as a lens, focusing the light which enters the eye. For this reason, it is very important that the cornea remains completely transparent. A number of diseases or scarring due to trauma can cause the cornea to lose transparency, which negatively affects vision. A corneal transplant can be done to replace a damaged cornea.
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