Ophthalmology General 600d1e8b Longest part of optic nerve A Intraocular B Intracranial C Intraorbital D Intracranial High-Yield Explanation The optic nerve is about 47- 50 mm in length and can be divided into 4 parts : intraocular (1mm), intraorbital (30mm), intracanalicular (6-9mm)and intracranial (10mm).