A 51-year-old male patient developed irreversible blindness following pulmonary tuberculosis treatment. The patient's medical history was reviewed, and thorough ophthalmologic examination undertaken (visual acuity, intraocular pressure, Kugel-Perimeter visual field checkup) on initial examination and throughout the next 2 years during the third month treatment with isoniazide, rifampicin, pirazinamide and ethambutol. Ocular symptoms occurred at 3 weeks of the initial symptoms, the patient was examined by an ophthalmologist, and treatment with ethambutol was discontinued; visual impairment progressed to bilateral optic nerve atrophy; almost no signs of improvement were found during the next 2 years of observation, in spite of treatment. Ethambutol is known to be an antituberculotic associated with ocular toxicity. Even in recommended dosage, ethambutol can lead to unpredictable and permanent damage to the optic nerve. The exact mechanism for optic neuritis has not yet been explained.