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': 'Diameter of the optic disc is – \nSelect and explain. \nA. 0.5 mm, B. 1.5 mm, C. 2.5mm, D. 3.5 mm', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Actually, optic disc is vertically oval with vertical diameter 1.88 mm and horizontal diameter 1.76 mm. However, some textbooks (like khurana) have metioned it as circular area of 1.5 mm diameter.', 'role': 'assistant'}]