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
Diameter of the optic disc is – 
Select and explain. 
A. 0.5 mm, B. 1.5 mm, C. 2.5mm, D. 3.5 mm
B: 1.5 mm
Answer: B: 1.5 mm 
Explanation: 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.