Vigabatrin Visual Field Loss — RACP Adult Medicine MCQ

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ModerateClinical PharmacologyVigabatrin Visual Field LossRACP Adult Medicine

A 60-year-old woman presents with a 2-week history of progressive bilateral visual field constriction. She has been on vigabatrin for 5 years for refractory epilepsy. Visual field testing shows bilateral concentric visual field constriction. What is the underlying mechanism?

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Correct answer: A — Pituitary macroadenoma

Vigabatrin causes irreversible retinal toxicity with bilateral concentric visual field constriction in 30–40% of patients on long-term therapy. The mechanism involves GABA-mediated retinal ganglion cell toxicity. Visual field testing (perimetry) must be performed at baseline and every 6 months during vigabatrin therapy. Once visual field defects are detected, they are IRREVERSIBLE, and vigabatrin should be ceased immediately (though the defect will not improve, cessation prevents progression). The risk-benefit assessment is particularly important as vigabatrin is primarily used for infantile spasms and refractory epilepsy where alternatives have failed.

Reference: AMH – 2025 – Vigabatrin; eTG – 2025 – Neurology