What is Marcus Gunn (Marcus Gunn pupil)?

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Last updated: May 1, 2025View editorial policy

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From the Research

Marcus Gunn pupil is a significant indicator of optic neuritis, which can be a precursor to multiple sclerosis, and patients presenting with this symptom should undergo further evaluation, including MRI scans, to assess the risk of developing multiple sclerosis 1. The presence of a Marcus Gunn pupil, characterized by a reduced pupillary light reflex in the affected eye, is a key diagnostic feature of optic neuritis, a condition that can lead to multiple sclerosis.

  • Optic neuritis is often the first clinical manifestation of multiple sclerosis, with a significant proportion of patients with multiple sclerosis developing optic neuritis at some point during their disease course 2.
  • The diagnosis of optic neuritis is based on a combination of symptoms, including pain on eye movement, subacute visual loss, and a weaker direct pupillary light reflex in the affected eye 1.
  • High-dosed intravenous methylprednisolone therapy can speed recovery from optic neuritis, but it does not improve the final outcome, and the risk of developing multiple sclerosis can be assessed with an MRI scan of the brain 3, 1.
  • For patients at high risk of developing multiple sclerosis, immune prophylaxis with beta-interferon or glatiramer acetate may be recommended to reduce this risk 1. The management of optic neuritis and the prevention of multiple sclerosis depend on early diagnosis and appropriate treatment, highlighting the importance of recognizing the Marcus Gunn pupil as a significant indicator of optic neuritis.

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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