For you to see clearly, your cornea and lens must bend, or refract, light rays and focus them on the retina, a layer of light-sensing cells that lines the back of the eye. The light rays are converted by the retina into impulses that are sent through the optic nerve to the brain, which recognizes them as images. If the light rays are not focused properly onto your retina, the image you see will be unclear. When this happens it is called a refractive error. The purpose of glasses, contacts and refractive surgery is to correct or reduce refractive errors by focusing light rays closer to or directly onto your retina. For information on correction of refractive errors see our Laser Vision Correction page.