Ethambutol-induced optic neuropathy: A case series

In this observational case series, we describe the clinical features and investigations of three patients with ethambutol-induced optic neuropathy (EION). All three patients had a significant visual loss within 3 months to 1 year of starting antitubercular treatment. Visual field examination revealed bitemporal hemianopia in one patient and central scotomas in another. Optical coherence tomography showed significant global thinning of the ganglion cell layer and thinning of the temporal quadrants of the retinal nerve fiber layer. Visual evoked potential revealed prolonged P1 or P2 latency and reduced amplitude in all three patients. Ethambutol was stopped in all three patients. The visual acuity continued to deteriorate even after stopping the drug but showed gradual improvement over a period of one and a half years. However, the visual recovery was not full in all three patients. Considering the severity and partially irreversible nature of the loss of vision caused by EION, it is imperative to detect it at an early and subclinical stage.