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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.
Causes A conduction defect in one optic nerve causes the afferent pupillary defect, but it does not account for unequal pupils, which is a separate entity that requires additional explanation if it occurs. The afferent pupillary defect (APD) is seen only in unilateral optic nerve disease.he response to this light reduction is the same as that in the first instance both pupils dilate to an appropriate amount. The afferent pupillary defect (Marcus Gunn pupillary escape phenomenon) depends on the light-reduction response that occurs in the presence of a conduction defect in the optic nerve.