The optic nerve is a cranial nerve (II) that is the special sensory nerve of sight. It enters the orbit through the optic canal and retains a meningeal sheath up to the point where it enters the back of the eye. Here, the meninges merge with the sclera of the eye. The optic nerve fibres enter the retina of the eye, and the remaining nerves (occulomotor, trochlear, and ophthalmic; V1) all pass through the superior orbital fissure. The ophthalmic nerve usually divides into three branches - the lacrimal, frontal and nasociliary nerves, just before passing through the fissure.