Optic Chiasmal Abnormality On MRI In Ethambutol Induced Bitemporal Hemianopia

Ethambutol induced optic neuropathy is known to cause central and cecocentral scotomas, but bitemporal visual field defects are also reported. The exact pathogenesis and location of the lesion in bitemporal hemianopia is poorly understood. Some authors suggest chiasm toxicity, while retinal lesions are also proposed based on abnormalities on multifocal electroretinogram. One study has shown focal axonal swelling without demyelination in the optic chiasm in rats exposed to ethambutol. But, chiasmal abnormalities on imaging are not reported in cases of bitemporal hemianopia with ethambutol use.