Multifocal electroretinographic abnormalities in ethambutol-induced visual loss.

Two patients who developed decreased visual acuity after several months of ethambutol treatment for Mycobacterium avium-intracellulare infection had bitemporal visual field defects that suggested optic chiasm damage. Multifocal electroretinography (mfERG) disclosed markedly low-amplitude responses at fixation and in the regions corresponding to the visual field defects. These results suggested that the visual dysfunction might be entirely attributable to retinal rather than optic nerve toxicity. These are the first reported patients to show mfERG abnormalities that correspond to bitemporal visual field defects and add to the growing evidence that ethambutol damages the retina.