The retina is the light-sensitive layer at the posterior, or back of the eye that covers about 65 percent of its interior surface. Light rays are focused onto the retina through our cornea, pupil and lens. Photosensitive cells called rods and cones in the retina convert incident light energy into signals that are carried by the optic nerve to the brain where they are interpreted as the images one observes . In the middle of the retina is a small dimple called the fovea or fovea centralis. The fovea is the center of the eye's sharpest vision and the location of most colour perception.