One of the most important structures in your eye is the cornea. The cornea is a thin, clear membrane that covers the outer part of the front of the eyeball. It's made primarily of a protein called collagen, which is very tough and strong. Because it's so tough and strong, it protects the delicate structures inside the eye from damage. In addition to protecting the eye, the cornea has another very important function for your vision. When you look at something, light goes into your eye and the cornea is the first thing it passes through. Since the cornea is a curved surface, it acts like a lens and begins to focus the light.