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: Ophthalmology
[{'content': 'Commonest cause of keratitis in soft contact lens users is: \nSelect and explain. \nA. Acanthamoeba, B. Staph aureus, C. Naegleria, D. Herpes', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A i.e. Acanthamoeba Pseudomonas aeruginosa is the most common organism encountered in contact lens related acute keratitis & corneal ulcer. Acanthamoeba is the 2nd most common cause.', 'role': 'assistant'}]