Amblyopia is often, incorrectly, referred to as "lazy eye", (see strabismus). It appears in early childhood. The visual system of one or both eyes fails to develop properly due to eye muscle misalignment, refractive (optical) reasons, or neurological abnormalities.

The eye muscle abnormality most often associated with amblyopia is the "crossed eye" (esotopia). The crossing eye is not being used and fails to develop properly. Treatment can include both eye patching of the good eye to force the "turned in eye" to develop, as well as a surgical procedure. Early fitting of spectacles can often correct "crossed eye" if the cause is refractive alone. Since the ocular system is usually completely developed by the seventh birthday, the detection of eye related problems during the child's first years can have lifelong consequences.

Medical Eye Associates and the American Academy of Ophthalmology recommend that an ophthalmologist evaluate all children before their first birthday, especially if a history of eye disease exists in the family. This is essential if the neurological causes of amblyopia are to be identified early.