This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Drug causing toxic optic neuropathy is:March 2009 
Select and explain. 
A. Pyrazinamide, B. Chloroquine, C. Ethambutol, D. Tetracycile
C: Ethambutol
Answer: C: Ethambutol 
Explanation: Ans. C: EthambutolCauses of nutritional optic neuropathy include tobacco, ethanol, thiamine, and vitamin B-12.Causes of toxic optic neuropathy include chemicals and drugs, such as methanol, ethylene glycol, ethambutol, isoniazid, digitalis, cimetidine, vincristine, cyclosporine, toluene, and amiodarone.Chloroquine causes loss of vision due to retinal damage. Corneal deposits may also occur and affect vision, but are reversible on discontinuation.