What does the cornea do?

The cornea is the clear “window” that allows light to pass into the eye. When the cornea is damaged, either by injury, allergies or disease, light rays entering the eye are scattered irregularly, decreasing one’s quality of vision.

The cornea acts as a barrier against dirt, germs, and other particles that can harm the eye. The cornea shares this protective task with the eyelids and eye sockets, tears, and the sclera (white part of the eye). The cornea also plays a key role in vision by helping focus the light that comes into the eye. The cornea is responsible for 65­-75 percent of the eye’s total focusing power.

The cornea and lens of the eye are built to focus light on the retina, which is the light-sensitive tissue at the back of the eye. When light strikes the cornea, it bends—or refracts—the incoming light onto the lens. The lens refocuses that light onto the retina, which starts the translation of light into vision. The retina converts light into electrical impulses that travel through the optic nerve to the brain, which interprets them as images.

The refractive process the eye uses is similar to the way a camera takes a picture. The cornea and lens in the eye act as the camera lens. The retina is like the film (in older cameras), or the image sensor (in digital cameras). If the image is not focused properly, the retina makes a blurry image.

The cornea also serves as a filter that screens out damaging ultraviolet (UV) light from the sun. Without this protection, the lens and the retina would be exposed to injury from UV rays.