Amblyopia, commonly called "lazy eye," is an eye condition in which one eye is not used enough for the visual system in the brain to develop properly. If one eye is weak, the brain ignores the images from it and uses only the images from the stronger eye, leading to poor vision in the weak eye.

Amblyopia usually affects only one eye, but it may occur in both eyes. Children can develop amblyopia between birth and about 7 years of age.

Amblyopia can be hard to detect. A child with amblyopia may have one eye that wanders or does not move with the other eye.

Amblyopia may develop if a child is much more nearsighted or farsighted in one eye than in the other. Extreme nearsightedness or farsightedness in both eyes may lead to amblyopia. Cloudiness in the black centre of the eye or a droopy upper eyelid also can lead to amblyopia.

Normal vision develops with regular, equal use of the eyes. Treatment for amblyopia includes patching the stronger eye to force the weaker eye to develop better vision. Early treatment can usually reverse the condition.