The cornea is the only part of the human body with no blood vessels and gets its oxygen directly from the air.

The cornea is the clear front window of the eye. It has five layers, including a thick middle layer called the stroma. The stroma contains organized fibers that let light pass through without scattering. If blood vessels grew into this area, it would cause vision loss or blindness.Oxygen moves into the cornea through a process called diffusion. When your eyes are open, oxygen from the air dissolves into your tears and enters the tissue. When your eyes are closed, the cornea gets a smaller amount of oxygen from the blood vessels in your eyelids.Because it lacks a direct blood supply, the cornea heals slower than other body parts. Wearing contact lenses for too long can block oxygen from reaching the eye. This can force the body to grow emergency blood vessels into the cornea, which can damage your sight.The cornea is also very sensitive. It has 300 to 600 times more nerves than your skin. This high sensitivity helps you blink or produce tears immediately if something touches your eye. This protects the surface that absorbs the oxygen you need to see clearly.