Cornea

The transparent front part of the eye that covers the iris, pupil, and anterior chamber, providing most of an eye’s optical power. The cornea has unmyelinated nerve endings sensitive to touch, temperature and chemicals; a touch of the cornea causes an involuntary reflex to close the eyelid. Because transparency is of prime importance the cornea does not have blood vessels; it receives nutrients via diffusion from the tear fluid at the outside and the aqueous humour at the inside and also from neurotrophins supplied by nerve fibers that innervate it.

The cornea is the only part of a human body that has no blood supply; it gets oxygen directly through the air. The cornea is the fastest healing tissue in the human body, thus, most corneal abrasions will heal within 24-36 hours.