Afferent pupillary defect

In medicine and neurology, afferent pupillary defect is a physical examination finding. "During the swinging-flashlight test, light shone into the healthy eye causes symmetrical pupillary constriction. Light directed into the abnormal eye causes bilateral pupillary dilatation, because of the reduced neural input that reaches the pretectal region of the midbrain. A relative afferent pupillary defect is typically found in the presence of a unilateral optic neuropathy and occasionally, but only rarely, with large macular abnormalities. It is usually present ipsilateral to the side of an injured optic nerve, whereas a postchiasmal optic-tract lesion will cause a contralateral relative afferent pupillary defect"