Amblyopia, also known as lazy eye, is a vision development disorder in which an eye fails to achieve normal visual acuity, even with prescription eyeglasses or contact lenses. Amblyopia begins during infancy and early childhood. In most cases, only one eye is affected. But in some cases, reduced visual acuity can occur in both eyes. Particularly if lazy eye is detected early in life and promptly treated, reduced vision can be avoided. But if left untreated, lazy eye can cause severe visual disability in the affected eye, including legal blindness.