Relative afferent pupillary defect (RAPD or APD): RAPD is a condition in which the left and right pupils respond differently to a bright light stimulus (shown in one eye at a time) due to unilateral or asymmetrical disease of the retina or optic nerve. The swinging flashlight (Marcus Gunn) test will show a brisk constriction of the pupil in the unaffected eye but when the bright light is moved to the damaged eye, the pupil dilates. In the normal optic nerve-to-brain anatomy, if either eye is exposed to a light stimulus, it is transmitted immediately to the brain, which then stimulates both pupils to constrict rapidly. If there is damage to one of the optic nerves, the transmission will be slower on that side and the brain interpretation will be of that the light is “dimmer” and, thus, the pupil will dilate.
Relative afferent pupillary defect (RAPD or APD) medical expert witness specialties include ophthalmology.