To form images of our environment, light emitted by or reflected from objects must be focused on the retina. Some of the light reflected from the surface of a yield sign is directed toward the eye. Upon reaching the eye, the light is first refracted by the cornea to send it on a path toward the retina. To reach the retina, the light rays must pass through the lens where a small amount of refraction adjusts the angle of the light to form a focused image on the retina. Central to the sense of vision is the transduction of light energy into electrical energy by cells in the retina called rods and cones. Cylindrical shaped cells called rods are responsible for the perception of light and dark. Conically shaped cells called cones are sensitive to red, green, or blue light.