refraction Bending of a wave, such as a light or sound wave, when it crosses the boundary between two media, such as air and glass, and undergoes a change in velocity. The incident wave (striking the surface), refracted wave and the normal (line perpendicular to the surface) all lie in the same plane. The incident wave and refracted wave make an angle of incidence, i, and an angle of refraction, r, with the normal. The index of refraction for a transparent medium is the ratio of the speed of light in a vacuum to its speed in the medium. Snell's law states that this ratio is constant for a given interface. See also reflection

refraction The bending of a ray which travels obliquely from one medium to another, at the interface separating the two; it is caused by the contrast in velocities with which the ray travels in the two media, and described by Snell's law. See also REFRACTION SURVEY.

refraction (ri-frak-shŏn) n. the change in direction of light rays when they pass obliquely from one transparent medium to another, of a different density. Refraction occurs as light enters the eye and passes through the cornea, lens, etc., to come to a focus on the retina. error of r. (refractive error) an abnormality of the eye, such as astigmatism or long- or short-sightedness, in which a blurred image forms on the retina due to abnormal focusing.
—refractive (ri-frak-tiv) adj.