The Cornea Has No Blood Vessels

For light to be focused properly, allowing us to see clearly, the eye's outer layer must be perfectly transparent. This necessity for clarity is the primary reason it lacks the blood vessels found in almost all other human tissues. Instead of receiving oxygen from blood, the cornea absorbs it directly from the atmosphere when our eyes are open, while nutrients are supplied by the tear film and a fluid called the aqueous humor from within the eye. This unique method of nourishment is essential for maintaining a clear, unobstructed window to the world.

This avascular nature provides the cornea with a status known as "immune privilege," which has significant medical implications. Because blood vessels that carry immune cells are absent, the risk of the body rejecting a transplanted cornea is much lower than with other organ transplants. For a long time, scientists were unsure of the exact mechanism preventing blood vessel formation. Recent discoveries have shown that proteins on the cornea's surface actively block the growth factors that would normally stimulate the development of blood vessels, thereby preserving its crucial transparency. This active process ensures our vision remains unimpeded by the structures that sustain the rest of our bodies.