Ethambutol induced optic neuropathy: A remerging ocular emergency needing strict vigilance and screening

: To investigate the clinical manifestations and incidence of ethambutol induced optic neuropathy (EON) and identify its risk factors. : A cross sectional, hospital based observational study was conducted in 100 patients, who were on anti-tubercular drugs (ATT) and complained of diminution of vision. The following data was collected in every patient regarding age, gender, co-morbid conditions, clinical manifestation of (tuberculosis)TB, duration and dose of ethambutol. Complete ophthalmic examination was conducted in every patient including best corrected visual acuity (BCVA), color vision, relative afferent pupillary defect (RAPD), fundus examination, visual field analysis and OCT RNFL & GCL. Statistical analysis of the data was done and represented suitably using appropriate statistical tests that included Chi Square test for checking associations and T test for comparing quantitative data with the help of SPSS ver. 26.0 software. All p-values reported were two sided and a value less than 0.05 was considered significant. :Out of 100 patients, only 18 patients were diagnosed with EON and calculated incidence was 1.8%. The most common presenting feature of EON was bilateral diminution of vision (89%) followed by abnormal color vision (11%). On examination, RAPD was seen in 40% cases because of asymmetrical optic nerve involvement and disc abnormality was present in 66% cases. The duration and dose of ethambutol medication, advanced age (>65 years), hypertension, chronic smoking and presence of renal dysfunction were shown to be positively correlated with EON development. :At present, there is no effective treatment for EON except supplementation of zinc, copper, methylcobalamine and pyridoxine. Therefore, early detection and discontinuation of ethambutol is only way to prevent permanent loss of vision, as in early stage it is reversible.