Role of Contrast Sensitivity and Optical Coherence Tomography (Oct) in Early Detection of Ethambutol Induced Toxic Optic Neuropathy a Hospital Based Prospective Study

Abstract

BACKGROUND Tuberculosis is one of the major diseases of public health importance in the world. Ethambutol hydrochloride is one of the first line drugs employed in the treatment of tuberculosis. The incidence of ethambutol induced toxic optic neuropathy is directly proportional to the dose and duration of ethambutol therapy. The aim of this study was to evaluate retinal nerve fibre layer thickness (RNFL) on optical coherence tomography (OCT) in patients on ethambutol therapy. MATERIALS AND METHODS This was a prospective study of 198 eyes of 100 patients being treated with ethambutol for tuberculosis at DOTS centre of Government Medical College, Srinagar. Visual acuity, contrast sensitivity and RNFL thickness on OCT were assessed. Examination was done before the start of therapy, after two months of treatment and two months after stopping ethambutol. RESULTS A total of 9/198 (4.54%) eyes demonstrated RNFL thinning on OCT after two months of ethambutol therapy. After two months of cessation of therapy, OCT changes were seen in 6/198 (3%) eyes. CONCLUSION The course of ethambutol induced ocular toxicity is unpredictable. Contrast sensitivity and RNFL thickness measurement are the early indicators of ethambutol induced optic neuropathy.