<prompt> Intraorbital length of the optic nerve -1 mm30mm6-9mm10mm  <response>: Ans. is b i.e., 30 mmo Optic nerve is about 47-50 mm in length and can be divided into 4 parts : -iIntraocular part 1 mm:It begins at optic disc optic nerve head and exits the nerve through a hole in sclera that is occupied by a mesh-like structure called the lamina cribrosa. The nerve fibres from the retina leave the eye through pores holes in lamina cribrosa, a sieve-like structure made up of collagen meshwork.iiIntraorbital part 30 mm:Extends from back of the eyeball at lamina cribrosa to the optic foramina.iiiIntracanalicular part 6-9 mm:It lies within the optic canal and closely related to ophthalmic artery which crosses obliquely over it.ivIntracranial part 10 mm:It lies above the cavernous sinus and converges with its fellow from contralateral side to form optic chiasma. 