Physics . the change of direction of a ray of light, sound, heat, or the like, in passing obliquely from one medium into another in which its wave velocity is different.

Ophthalmology .

the ability of the eye to refract light that enters it so as to form an image on the retina.

the determining of the refractive condition of the eye.

Astronomy .

Also called astronomical refraction. the amount, in angular measure, by which the altitude of a celestial body is increased by the refraction of its light in the earth's atmosphere, being zero at the zenith and a maximum at the horizon.

the observed altered location, as seen from the earth, of another planet or the like due to diffraction by the atmosphere.