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': 'Most common adverse effect on eye in contraceptive usage is: \nSelect and explain. \nA. Colour blindness, B. Ring scotoma, C. Optic neuritis, D. Nystagmus', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. Optic neuritis', 'role': 'assistant'}]