Your cornea is the clear layer on the front of your eyeball. It protects your eyeball from dust and germs and helps filter out harmful ultraviolet, UV, rays. The cornea also helps to focus light entering your eye. Although your cornea is composed of strong proteins, it can be injured. A slight cut or scratch, abrasion, is often minor. But a bad abrasion or a puncture to the cornea can be very serious and can affect your vision. These are medical emergencies.