Ethambutol-induced optic neuropathy: Another conundrum

Purpose: The purpose was to study the effect of ethambutol (EMB) and cause for optic neuropathy in the hope that better understanding of the condition will help us to reduce the burden of visual loss. Materials and Methods: A retrospective analysis of patients with EMB-induced optic neuropathy was done, which included 30 patients attending our outpatient department from January 2022 to March 2022. Results: The mean age was 53.73 with male (70%) preponderance. Visual fields showed bitemporal hemianopia in 43% (13), temporal field defects in 26% (8), centrocecal scotoma in 17% (5), and low reliability in 10% (3). Visual evoked potential amplitude was reduced in 87% (26). Magnetic resonance imaging showed enhancement of optic chiasma in 40% (12). After discontinuing and replacing EMB, with Vitamin B complex and zinc supplements, 53% (16) had visual improvement on 1-month follow-up. Conclusion: India has launched the Pradhan Mantri TB Mukt Bharat Abhiyan “Ni-kshay 2.0” portal to eradicate tuberculosis by 2025. Hence, aggressive treatment protocols are underway. The increased duration of EMB in new directly observed therapy short-course regimen has caused increased incidence of EMB optic neuropathy. Regular screening is needed to diagnose and prevent further visual deterioration in these patients. Timely replacement of the drug with another drug is a key in visual recovery of these patients. Further studies are needed to assess if the genetic predisposition is responsible for optic nerve damage.