The cornea is the clear, curved front window of your eye. When you look at your eye in the mirror, the cornea is the transparent dome covering the colored part (your iris) and the black circle in the center (your pupil). You can't actually see the cornea itself because it's completely clear, like a contact lens, but you're looking through it right now as you read these words.

The cornea does two important jobs. First, it protects your eye from dust, germs, and anything else that might damage it. Second, it bends incoming light to help focus images on the back of your eye, working together with the lens behind it. In fact, the cornea does most of the focusing work in your eye.

Because the cornea must stay crystal clear for you to see properly, it has no blood vessels running through it, unlike most parts of your body. Instead, it gets oxygen directly from the air and nutrients from the tears covering its surface. When someone has a damaged or cloudy cornea, doctors can sometimes perform a cornea transplant, replacing the damaged tissue with healthy cornea tissue from a donor cornea.