The cornea is your eye’s clear, protective outer layer. Along with the sclera (the white of your eye), it serves as a barrier against dirt, germs, and other things that can cause damage. Fun fact: Your cornea can also filter out some of the sun’s ultraviolet light. But not much, so your best bet to keep it healthy is to wear a pair of wraparound sunglasses when you’re outdoors.

It also plays a key role in vision. As light enters your eye, it gets refracted, or bent, by the cornea’s curved edge. This helps determine how well your eye can focus on objects close-up and far away.

If your cornea is damaged by disease, infection, or an injury, the resulting scars can affect your vision. They might block or distort light as it enters your eye.