Amblyopia, also called lazy eye, is a disorder of sight. It results in decreased vision in an eye that otherwise appears normal, or out of proportion to associated structural problems of the eye.

Whenever the brain does not receive visual signals from an eye for a long period of time, there is a risk of amblyopia. It also can occur when the brain "turns off" the visual processing of one eye to prevent double-vision, for example in strabismus (crossed eyes). The cause of amblyopia is within the brain.