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': 'The 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: "Pseudomonas aeruginosa is the most common organism encountered in contact lens-related acute keratitis and\xa0corneal ulcer".\n-\xa0Holland & mannis\nAcanthamoeba is the 2nd\xa0most common cause.', 'role': 'assistant'}]