Evaluation of visual functions in patients on ethambutol therapy for tuberculosis: a prospective study

To study the incidence of clinical and subclinical optic nerve toxicity with ethambutol therapy in patients with tuberculosis and to evaluate the reversibility of its side effects after cessation of therapy. This prospective randomized controlled study included 60 newly diagnosed adult cases of tuberculosis, who were randomly assigned into two groups. The study group included 30 patients (60eyes) who received ethambutol as a part of their anti-tubercular treatment and the control group included 30 patients (60eyes) who did not receive ethambutol. The patients were examined on monthly basis. The visual parameters studied were best corrected visual acuity, pupillary reactions, optic disc changes, color vision, contrast sensitivity, pupil cycle time, visual field charting and visual evoked potential. Ethambutol was stopped in those patients in whom toxicity was detected and they were followed more frequently. Only one patient (3.3%) showed decrease in visual acuity, three patients (10%) developed visual field defects, two patients (6.7%) showed deterioration of contrast sensitivity, the pupil cycle time was prolonged in one eye and two patients (6.7%) showed abnormal visual evoked potential. During the therapy, all patients in the study group had normal pupillary reactions, fundus picture and color vision.

Ethambutol induced ocular toxicity was seen in three patients (10%) in our study. The maximum visual recovery occurred in first six to eight weeks after stopping ethambutol. The visual recovery was complete in only one patient, but it was partial in two patients i.e. visual fields, contrast sensitivity and visual evoked potential remained abnormal.