Retrobulbar neuritis is seen with :

The most impoant side effect is optic neuritis, resulting in decreased visual acuity and loss of ability to differentiate red from green. The incidence of this reaction is propoional to the dose of ethambutol and is observed in 15% of patients receiving 50 mg/kg/day, in 5% of patients receiving 25 mg/kg/day, and in <1% of patients receiving daily doses of 15 mg/kg. The intensity of the visual difficulty is related to the duration of therapy after the decreased visual acuity first becomes apparent and may be unilateral or bilateral. Tests of visual acuity and red-green discrimination prior to the sta of therapy and periodically thereafter are thus recommended. Recovery usually occurs when ethambutol is withdrawn; the time required is a function of the degree of visual impairment. Ref : Gumbo T. (2011). Chapter 56. Chemotherapy of Tuberculosis, Mycobacterium Avium Complex Disease, and Leprosy. In B.C. Knollmann (Ed), Goodman & Gilman's The Pharmacological Basis of Therapeutics, 12e.