The Cornea Has No Blood Vessels

The human eye's remarkable ability to focus light begins with its outermost layer, the cornea. For vision to be sharp and unobstructed, this tissue must be perfectly transparent. This absolute clarity is achieved through a critical biological trade-off: the cornea is completely avascular, meaning it lacks the blood vessels found in almost all other living tissues. If blood vessels were present, they would scatter light and cloud our vision, much like looking through a frosted window. Along with cartilage, it stands as a rare example of living tissue that forgoes a direct blood supply for the sake of its specialized function.

Instead of relying on blood, the cornea has a dual-source system for survival. It absorbs oxygen directly from the atmosphere through the tear film that coats its surface and draws essential nutrients from the aqueous humor, the fluid filling the chamber directly behind it. This unique anatomy has a fascinating consequence known as "immune privilege." Because blood vessels act as highways for the body's immune cells, their absence makes the cornea a relatively protected site. This is a primary reason why corneal transplants have one of the highest success rates of any transplant procedure, as the risk of the recipient's body rejecting the new tissue is significantly lower.