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Ethambutol Optic Neuritis — SCE Infectious Diseases MCQ

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EasyTuberculosisEthambutol Optic NeuritisSCE Infectious Diseases

A 50-year-old man with treated pulmonary TB develops visual loss at week 8 of treatment. Visual acuity is reduced bilaterally and colour vision testing (Ishihara plates) shows red-green deficit. Fundoscopy is normal. What is the diagnosis and management?

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Correct answer: D — Ethambutol-induced optic neuritis — stop Ethambutol immediately and refer to ophthalmology; visual loss is usually reversible if detected early

Ethambutol causes dose-dependent retrobulbar optic neuritis affecting visual acuity and colour vision (red-green most commonly). Fundoscopy is typically normal in early disease (retrobulbar — behind the eye). Ethambutol MUST be stopped immediately upon detection of visual symptoms. Visual loss is usually reversible if caught early, but can be permanent if treatment continues. Baseline visual acuity and Ishihara colour testing should be performed before starting Ethambutol and monthly during treatment. Higher doses (>15 mg/kg) increase risk.

Reference: NICE NG33 2016 – TB; BNF 2024 – Ethambutol; RCOphth 2023