The deviation of rays of light on passing from one transparent medium into another of different density. The refractive surfaces of the EYE are the anterior surface of the cornea (which accounts for approximately two-thirds of the focusing or refractive power of the eye), and the lens (one-third of the focusing power of the eye). The refractive power of the lens can change, whereas that of the cornea is fixed. (For errors of refraction, see under EYE, DISORDERS OF.)