Relative afferent pupillary defect
A relative afferent pupillary defect (RAPD), also known as a Marcus Gunn pupil, is a medical sign observed during the swinging-flashlight test whereupon the patient's pupils dilate when a bright light is swung from the unaffected eye to the affected eye. The affected eye still senses the light and produces pupillary sphincter constriction to some degree, albeit reduced.
| Relative afferent pupillary defect | |
|---|---|
| Other names | Marcus Gunn pupil |
| The left optic nerve and the optic tracts. A Marcus Gunn pupil indicates an afferent defect, usually at the level of the retina or optic nerve. Moving a bright light from the unaffected eye to the affected eye would cause both eyes to dilate, because the ability to perceive the bright light is diminished. | |
| Specialty | Ophthalmology, Optometry |
Depending on severity, different symptoms may appear during the swinging flash light test:
Mild RAPD initially presents as a weak pupil constriction, after which dilation occurs.
When RAPD is moderate, pupil size initially remains same, after which it dilates.
When RAPD is severe, the pupil dilates quickly.
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