Both treatment duration and interval from vision loss onset to ethambutol cessation are important markers for visual acuity in optic neuropathy associated with ethambutol therapy, according to research published in the Journal of Ophthalmology & Clinical Research.
Researchers conducted a retrospective, observational, single-center study of consecutive patients at the Aravind Eye Hospital in Coimbatore, India between July and October 2019. They examined visual decline in patients with ethambutol-related optic neuropathy and assessed visual recovery following medication cessation.
A cohort of 30 patients (18 men; mean age, 54±13 years) were included. Researchers recorded visual acuity and visual evoked potentials for each eye and measured changes. All patients were being treated with some combination of antituberculous treatment — including ethambutol 15 to 25 mg/kg/day — for an average of 7±4 months. Average interval from vision loss onset to ethambutol discontinuation was 4.4±3.8 months.
After discontinuing ethambutol, treatment was continued with isoniazid and rifampicin, and ethambutol was replaced with levofloxacin.
At baseline, mean visual acuity of all patients was 0.25±0.25 (0.57 logMAR). At 3 months follow-up, visual acuity improved to 0.45±0.36 (0.35 logMAR).
After evaluating patients who were on ethambutol therapy for longer than 8 months, investigators found that the average presenting vision was 0.4±0.28 (0.40 logMAR), and 0.69±0.33 (0.16 logMAR) at follow-up. Patients on ethambutol therapy for less than 8 months had an average presenting vision of 0.18±0.16 and vision at follow-up of 0.27±0.24 (0.75 and 0.57 logMAR, respectively). Presenting and follow-up visual acuities were statistically significantly better in patients on ethambutol therapy for longer than 8 months.
Patients who stopped ethambutol for 4 or more weeks following their initial vision loss presented with an average vision of 0.17±0.15, with vision of 0.37±0.28 (0.77 and 0.44 logMAR, respectively); those who stopped less than 4 weeks after vision loss had average vision of 0.36±0.3 and 0.57±0.4 (0.44 and 0.24 logMAR) at baseline and follow-up, respectively, and at follow-up, visual acuity remained worse in the greater than 4-week group — but did not reach statistical significance.
Patients on ethambutol therapy for 8 months or longer had a mean visual evoked potential (VEP) amplitude of 2.0±1.8 µV, vs 1.8±1.37 µV in those on less than 8 months of therapy. This difference was not statistically significant.
Mean VEP amplitude was 1.4±0.93 µV in patients who discontinued ethambutol 4 weeks or longer following vision decline, compared with 2.4±2.02 µV in patients who stopped treatment less than 4 weeks after visual decline. This difference was statistically significant and consistent with the differences in visual acuity noted between the 2 groups.
Study limitations include the small sample size and lack of VEP results after visual improvement.
“Not surprisingly, patients who took longer to stop ethambutol presented with worse vision than patients who stopped it sooner. However, both groups recovered similar vision after cessation,” according to the researchers. “These findings support prompt cessation of ethambutol after presumed optic neuropathy to prevent visual decline, but it seems the total duration of treatment is more important for final visual prognosis than is the duration of time to cessation.”
MacIntosh PW, Balian D, Kumar K, Shah VM. Ethambutol optic neuropathy visual function and visual evoked potentials. J Ophthalmic Clin Research. 2020;7:071. doi:10.24966/OCR-8887/100071