A prospective evaluation of ocular toxicity in patients receiving ethambutol as anti-tubercular therapy

Purpose: The purpose of this study was to detect the early ocular toxicity of ethambutol in tuberculosis patients. Materials and Methods: This was a prospective, nonrandomized noncomparative cross-sectional cohort study of consecutive 93 patients (186 eyes) getting anti-tubercular therapy, including ethambutol (15–20 mg/kg/day) along with isoniazid, rifampicin, and pyrazinamide. The duration of the study was 1 year from June 1, 2018 to May 31, 2019. Best-corrected visual acuity (BCVA), color vision, visual field, contrast sensitivity, pattern-reversal visual evoked responses (VER), and retinal nerve fiber layer (RNFL) thickness measurements were done in both eyes of each patient at baseline and thereafter at 1st, 2nd, and 6th months of therapy. Results: Mean age of the patients was 29.38 ± 8.43 years (range 11–58 years). Among them, 53 were male and 40 were female. All the visual parameters were normal at baseline and 1st month of therapy. Mean BCVA was significantly decreased at the 2nd month but improved at the 6th month. In the 2nd month of treatment, abnormal color vision was detected in 8 patients (16 eyes; 8.6%). Three patients developed bilateral central scotoma, which persisted in two patients even after 6 months of follow-up. The mean latency in VER was significantly increased from baseline at 2nd and 6th months of therapy. The mean contrast sensitivity in both eyes was significantly decreased from baseline at the 2nd month of therapy but improved at 6th month. Mean temporal RNFL thickness was significantly reduced from baseline assessment after 2 and 6 months of treatment. Conclusion: The assessment of BCVA, Colour vision, Visual field, Contrast sensitivity, VER, and RNFL thickness measurements are essential at baseline and thereafter at monthly intervals to detect early ocular ethambutol toxicity.