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': 'Earliest symptom of retinitis pigmentosa – \nSelect and explain. \nA. Ring scotoma, B. Night blindness, C. Tubular vision, D. None', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Night blindness (nyctalopia) is the earliest symptom.', 'role': 'assistant'}]