<prompt> All are true about optic nerve except -a Arises from axons of bipolar neuronsb 4 cm longc Covered by 3 layers continuous with meningesd Crossed by ophthalmic arteryacabadbc  <response>: The neurosensory layer of retina contains three mains neurosensory cells: - Photoreceptors, i.e. rods cones; bipolor cells in inner nuclear layer; and ganglionic cells in ganglionic cell layer. Axons of ganglionic cells multipolar cells form the optic nerve.Length of optic nerve is 47-50 mm.Like other parts of CNS, the optic nerve is covered by meningeal sheaths Pia, arachnoid and dura mater as soon as it leaves the eyeball.Intercanalicular part of optic nerve is crossed by ophthalmic artery. 