Objective: To report the abnormal multifocal electroretinogram (mfERG) findings in two cases of presumed ethambutol toxicity. Design: Retrospective observational case series. Participants: Two patients with ethambutol toxicity and visual loss. Testing: Multifocal electroretinography. Main outcome measure: Waveform measurements on multifocal electroretinography. Results: Two patients with bilateral visual loss due to ethambutol toxicity underwent mfERG testing that disclosed both diffuse and central field loss compatible with retinal dysfunction as a contributing mechanism to the visual field loss. Conclusion: Ethambutol toxicity affects not only the optic nerve but probably other retinal elements based upon abnormal mfERG findings.
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