An afferent pupillary defect is an eye condition where one eye is less sensitive to light, and will not contract as sharply in response to light as the unaffected eye.This can be a sign of optic nerve damage, tumor, glaucoma, and a number of other eye issues.n afferent pupillary defect may be a sign of damage to the optic nerve. An afferent pupillary defect may be a sign of glaucoma or other eye conditions.