Ethambutol optic neuropathy with correspondent chiasmitis manifestation in magnetic resonance imaging

We present a case of an older patient with toxic chiasmatic optic neuropathy accompanied by bitemporal hemianopia associated with ethambutol use. The patient experienced gradual visual defect recovery that was concurrent with an improvement of chiasmal enhancement in the repeat magnetic resonance imaging performed at his 6-month follow-up. However, his visual field pattern sharply changed to left inferior homonymous quadrantanopia because of a new episode of occipital lobe infarction. After 2 years, the patient's visual function reached the best-corrected visual acuity of 20/20 in both eyes, although he had the sequela of homonymous quadrantanopia related to the infarction. Optical coherence tomography revealed that the loss on the macular ganglion cell–inner plexiform layer was related to retrograde transsynaptic degeneration caused by ethambutol-related chiasmopathy.