From HomoExcelsior

1. The turning or bending of any wave, such as a light or sound wave, when it passes from one medium into another of different density. 2. The apparent change in position of celestial objects caused by the bending of light rays entering Earth's atmosphere. 3. The ability of the eye to bend light so that an image is focused on the retina. 4. Determination of the refractive characteristics of the eye.

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