The cornea has five distinct layers. From the outermost inward, these are the epithelium, Bowman's membrane, stroma, Descemet's membrane, and endothelium. The uniform spacing of the collagen fibers within the stroma accounts for the cornea's transparency. No blood vessels normally exist within the cornea. Its nutrition is mostly derived from the vascular limbus and from atmospheric oxygen.
Lymphatic drainage is absent.
The corneal epithelium prevents organisms from entering the eye. It is approximately 50 micrometers thick. Bowman's layer measures nearly 10 micrometers its function is unknown. The endothelium consists of a single layer of cells that acts as a pump to keep the cornea deturgescent. Because there are nerve endings in close proximity to the corneal epithelium, even slight exposure, as with corneal abrasion, may result in significant pain.