Clinical profile and visual outcomes in ethambutol-induced toxic optic neuropathy

To characterize the severity of vision loss, dose-related adverse effects, and visual outcomes in ethambutol-induced toxic optic neuropathy (ETON) patients.

A prospective observational study was conducted in a tertiary eye center in South India between July 2019 and December 2021. Consecutive adults (age >18 years) taking revised antitubercular regimens and diagnosed with ETON were included. Data collected regarding patient demographics, presentation, dose-related severity of vision loss, and visual outcomes after drug discontinuation were analyzed.

We analyzed 214 eyes from 107 patients (mean age: 51.1 ± 13 years; male: female ratio = 2:1). The median follow-up time was 11 months (interquartile range: 4-14 months). Mean visual acuity improved from 1.2 ± 0.6 log of minimum angle of resolution (logMAR) at presentation to 0.8 ± 0.6 logMAR at the final follow-up. Patients above 60 years old had the worst visual acuity at presentation and had the least improvement at the last follow-up compared to those in younger age groups (1.3-1.2 logMAR, P = 0.2). The mean exposure time to ethambutol was 6.8 ± 3.3 months, and the mean dose was 1042 ± 247 mg/day, that is, 16.7 ± 4 mg/kg/day. Mean presenting best corrected visual acuity (BCVA; 1.3 ± 0.6 logMAR) was worse in patients taking a higher dose of ethambutol (≥16 mg/kg) compared to those taking <16 mg/kg (mean BCVA: 1 ± 0.5 logMAR).

Higher age and higher doses of ethambutol were associated with an increased risk of vision loss and worse vision at presentation. Prolonged exposure to high-dose ethambutol, as in fixed drug dose combinations, leads to severe visual impairment which might be partially reversible.