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Marcus Gunn pupil
System: Neurological Signs · All neurological signs
What it is — and how it is elicited
In the swinging light test, the pupil of the affected eye paradoxically dilates when the light is swung onto it — a relative afferent pupillary defect.
What a positive finding suggests
Associated with optic nerve disease or extensive retinal damage on that side.
◈ Behind the name
Robert Marcus Gunn (1850–1909), Scottish ophthalmologist.
Related signs — Neurological Signs
Browse the M section of the A–Z list or return to the Clinical Signs hub.
Please note: This page is an educational reference about clinical examination signs. A clinical sign supports — and never replaces — a full clinical evaluation, examination and appropriate testing. A sign being present does not by itself prove a diagnosis, and an absent sign does not rule one out. If you have symptoms that worry you, see a health professional.