Amblyopia: the normal eye is not normal.

When acuity was used to evaluate amblyopia in children, the amblyopic eye had decreased acuity and the nonamblyopic eye had normal acuity. However when Contrast Sensitivity Functions (CSFs) were used to evaluate amblyopia, losses in the CSF were discovered in both the amblyopic and the nonamblyopic eyes. During the course of occlusion therapy, the amblyopic eye improved in acuity and CSF and the nonamblyopic eye improved in CSF. The results suggest that the nonamblyopic eye is not normal and that the CSF provides additional information to acuity about amblyopia in children.