Prospective evaluation of ethambutol toxic optic neuropathy in patients of pulmonary tuberculosis

The aim of the study was to evaluate visual parameters for early detection of ethambutol toxicity to prevent irreversible optic nerve damage. This cohort study included 50 newly diagnosed cases of pulmonary tuberculosis, i.e. 100 eyes, in people aged 18–72 years, who received ethambutol as part of the antitubercular therapy. Before starting antitubercular treatment, at each monthly visit, ophthalmic examination was done that included best corrected visual acuity, optic disc evaluation, colour vision, contrast sensitivity, pupil cycle time and automated perimetry for a period of six months. Ethambutol was discontinued in patients who showed signs of visual impairment. These patients were observed for another three months for reversibility of toxicity. Visual functions were normal in all patients at baseline. Out of 50 patients, 47 didn't show any signs of deterioration in visual functions even after six months of oral administration of ethambutol. However, 3 out of 50 patients, i.e. 6 eyes (6 %), showed signs of toxicity after 4–5 months – LogMAR visual acuity deteriorated from 0.00 to 1.08 (±0.40); mean contrast sensitivity deteriorated from 1.725 (±0.075) to 1.12 (±0.18); mean deviation in visual fields got impaired from −1.37 (±0.15) to −10.93 (±2.66); and colour vision got severely affected. All the affected patients were aged above 65. In the present study, six percent of 50 patients showed ethambutol toxic optic neuropathy. It was concluded that patients should be comprehensively evaluated for visual parameters before starting the ethambutol treatment. They should be closely monitored by an ophthalmologist for visual functions every month to detect ethambutol toxicity at the early reversible stage to prevent irreversible damage to the optic nerve. Patients should be asked to report immediately if they detect any blurring of vision or colour vision abnormality.