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
Which is the smallest part of optic nerve 
Select and explain. 
A. Intraocular, B. Intraorbital, C. Intracanalicular, D. Intracranial
A: Intraocular
Answer: A: Intraocular 
Explanation: Intraocular - 1 mm.
Intraorbital - 30 mm.
Intracanalicular - 6-9 mm.
Intracranial - 10 mm.