Relative afferent pupillary defect
medical sign observed during an eye test
A relative afferent pupillary defect (RAPD), also known as a Marcus Gunn pupil (after Robert Marcus Gunn), is a medical sign observed during the swinging-flashlight test whereupon the patient's pupils excessively 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.
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.
Presentation
Cause
Normally, the optic nerve is responsible for sensing light while the oculomotor nerve is responsible for contracting the pupil in response to this light.
The most common cause of Marcus Gunn pupil is a lesion of the optic nerve (between the retina and the optic chiasm) due to glaucoma, a severe retinal disease, or due to multiple sclerosis. It is named after Scottish ophthalmologist Robert Marcus Gunn.
A second common cause of Marcus Gunn pupil is a contralateral optic tract lesion, due to the different contributions of the intact nasal and temporal hemifields.
Diagnosis
The Marcus Gunn pupil is a relative afferent pupillary defect indicating a decreased pupillary response to light in the affected eye.
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This entry incorporates text from “Relative afferent pupillary defect” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.