You can use traditional clinical techniques, such as fixation behavior, to tell if an eye is amblyopic, or lazy, in preverbal children. However, these techniques cannot accurately determine how well the eye sees. The pattern VEP is a sensitive and quantitative detector of amblyopia.  VEP acuity measures are useful in monitoring acuity in the patched preverbal infant and in detecting occlusion amblyopia caused by patching too long.