This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Neuro Ophthalmology, Subject name: Ophthalmology
[{'content': 'Which of the following pa of optic nerve is longest? \nSelect and explain. \nA. Intraorbital, B. Intraocular, C. Intracranial, D. Intracanalicular', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Intra-orbital is the longest pa of optic nerve. Cranial Nerve Optic nerve arises from ganglion cell axons. Length = 50 mm. (40 mm in few texts) Can be considered as pa of brain 2nd order neuron Pas: Intraocular(1), Intraorbital(2), Intracanalicular(3), Intracranial(4). Smallest pa of optic nerve is Intraocular Longest pa : Intraorbital.', 'role': 'assistant'}]