Professional
Technical
IVT
Marcus Gunn pupil
Pronunciation: MAR-kus GUN PYOO-pil
Abnormal pupil response indicating optic nerve dysfunction, detected by the swinging flashlight test.
Full Definition
A Marcus Gunn pupil, also known as a relative afferent pupillary defect (RAPD), is an abnormal pupillary response that indicates dysfunction of the optic nerve or severe retinal disease. When light is swung from the normal eye to the affected eye, the affected pupil paradoxically dilates instead of maintaining constriction. This finding suggests asymmetric disease affecting the afferent visual pathway and requires immediate ophthalmologic evaluation to rule out serious conditions like optic neuritis or retinal detachment.
Usage
Usage note: Grade the severity (1+ to 4+) when documenting RAPD findings.
In Context
- "A 2+ Marcus Gunn pupil was detected in the left eye, prompting urgent MRI evaluation." — Emergency consultation note
- "The absence of a Marcus Gunn pupil helped rule out optic nerve involvement." — Neurological assessment
Also known as
RAPD
relative afferent pupillary defect
Contrasted with
normal pupillary response
Don't confuse with
Adie's pupil
Horner's syndrome