Amblyopia:

Anisometropic amblyopia (lazy eye) is a major ophthalmic public health problem where one eye sees normally and the other eye has partial blindness from an uncorrected refractive error. Amblyopia is the most common cause of reversible blindness in children in the United States affecting approximately 200,000 Americans with 2-4% of all children affected. If detected and treated during the preschool years, the outcome is favorable. If a child reaches 7 to 9 years of age, treatment becomes exceedingly more difficult and often irreversible legal blindness will be permanent in the affected eye. Affected children and their parents often are unaware that the vision is coming from only on eye.