Multifocal electroretinographic abnormalities in ethambutol-induced visual loss

Area of Science:

• Ophthalmology
• Neuroscience
• Infectious Diseases

Background:

• Ethambutol is a key antibiotic for treating Mycobacterium avium-intracellulare infections.
• Ocular toxicity, including optic neuropathy, is a known but not fully understood side effect of ethambutol.
• Assessing the precise location and mechanism of ethambutol-induced visual dysfunction is crucial for patient management.

Observation:

• Two patients undergoing ethambutol therapy for Mycobacterium avium-intracellulare infection presented with decreased visual acuity.
• Bitemporal visual field defects were observed, initially suggesting optic chiasm involvement.
• Multifocal electroretinography (mfERG) was performed to evaluate retinal function.

Findings:

• mfERG demonstrated significantly reduced responses at the fixation point.
• Abnormal mfERG responses corresponded precisely to the areas of the bitemporal visual field defects.
• The pattern of mfERG abnormalities strongly indicated retinal toxicity rather than optic nerve damage.

Implications:

• These findings suggest that ethambutol may primarily cause retinal damage, leading to specific visual field impairments.
• This case series is the first to correlate mfERG abnormalities with bitemporal visual field defects in ethambutol toxicity.
• The results contribute to the understanding of ethambutol's ocular side effects, emphasizing potential retinal toxicity.