Ethambutol (EMB) is an antibiotic used to treat infection by Mycobacterium species, particularly Mycobacterium tuberculosis and non- tubercular infections like M. avium complex and M. kansasii. Unfortunately, one serious and vision threatening side effect of EMB is ethambutol-induced optic neuropathy (EON). [1] Less common side effects of EMB include peripheral neuropathy, cutaneous reactions.