Definition of Anisometropia

Anisometropia: The condition in which the two eyes have unequal refractive power. One eye may be myopic (nearsighted) and the other hyperopic (farsighted) or one eye may be markedly stronger than the other.

Anisometropia is a serious concern in newborns and young children because it can lead to amblyopia (impaired vision in one eye). With a major degree of anisometropia, the brain cannot reconcile the difference in images coming from the two eyes. It develops a preference for the image coming from one eye and suppresses the image from the other eye and, in time, the brain loses the ability to "see" the image from the suppressed eye.

Anisometropia is derived from Greek and made up of four parts: an-, -iso-, -metr-, and -opia. Their meaning (in parentheses) is simple. An- (not) + -iso- (equal) + -metr- (measure) + -opia (vision). Literally, the measure of vision is not equal. The refractive power of the two eyes is different. The opposite of anisotropia is isometropia. In isometropia, the refractive power is equal in both eyes.