Define the disease - Marcus Gunn Pupil (RAPD)
Relative Afferent Pupillary Defect occurs in a pupil of an eye that is blirld from optic nerve disease. When light is shifted to the affected pupil it will dilate instead of remaining constricted. This happens because the input from the optic nerve to the midbrain from the affected side is less than from the normal side. A Swinging flashlight test can be performed to confirm this disorder.