Multifocal electroretinogram demonstrated macular toxicity associated with ethambutol related optic neuropathy

Ethambutol is an effective drug in the first line treatment for tuberculosis but its use may be associated with ocular toxicity.¹ Toxic optic neuropathy is the most important ocular side effect and is related to the dose and duration of treatment.² It is usually bilateral and both central and peripheral types of optic neuropathy have been described. The central type involves the papillomacular bundle and results in decreased visual acuity, caecocentral scotoma, and blue-yellow colour vision loss, whereas the peripheral type causes peripheral visual field loss, especially bitemporal defects with sparing of visual acuity and red-green colour vision impairment.³ In additional to the optic nerve toxicity, studies have also demonstrated that ethambutol may also be toxic at the retinal level.^4–6 We report a patient with ethambutol related toxic optic neuropathy associated with bilateral macular toxicity as demonstrated by multifocal electroretinogram (mfERG). To our knowledge, evaluation …