Marcus Gunn phenomenon

Marcus Gunn phenomenon (also known as Marcus Gunn pupil or relative afferent pupillary defect (RAPD)) is a medical condition that affects the eyes. It is named after the Scottish ophthalmologist Robert Marcus Gunn, who first described it in 1902.

Overview

The Marcus Gunn phenomenon is a relative afferent pupillary defect indicating a problem with the afferent limb of the pupillary light reflex. It is usually caused by severe retinal disease or optic nerve damage. The condition is often associated with glaucoma, retinal detachment, optic neuritis, and central retinal artery occlusion.

Symptoms

The main symptom of the Marcus Gunn phenomenon is an abnormal pupillary light reflex. When light is shone into the affected eye, the pupil may dilate instead of constricting. This is known as a "swinging flashlight test". Other symptoms may include vision loss, blurred vision, and pain in the eye.

Diagnosis

The diagnosis of Marcus Gunn phenomenon is typically made through a clinical examination, including the swinging flashlight test. Additional tests may include visual field testing, optical coherence tomography, and magnetic resonance imaging (MRI) to assess the extent of optic nerve damage.

Treatment

Treatment for Marcus Gunn phenomenon is aimed at addressing the underlying cause. This may involve treating the associated conditions such as glaucoma, retinal detachment, or optic neuritis. In some cases, surgery may be required to repair the damaged optic nerve or retina.

See also

• Leber's hereditary optic neuropathy
• Optic disc pallor
• Optic neuropathy

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