Cranial nerve 2 is all about the special sense of vision, or sight. It has nothing to do with where you’re looking, the shape of the lens, or the size of the pupil – those things are the job of other cranial nerves. The optic nerve is only about light hitting cells that gets translated in the brain as having seen something.
Special sense of vision using cranial nerve 2
Cranial nerve 2 contains Special Somatic Afferent (SSA) fibers for vision (check out this post to learn more about types of fibers). It begins as bipolar neurons in the retina. The axons leave the retina to form the optic nerve, encased by meningeal layers (pia, arachnoid, and meningeal dura mater) as it passes through the orbit towards the optic canal.
The optic canal, a hole within the lesser wing of the sphenoid bone, contains cranial nerve 2 and the ophthalmic artery. A branch of the ophthalmic a., the central artery of the retina, supplies the retina, having branched to run in the middle of the optic nerve.
Left and right optic nerves meet to form the optic chiasm. This structure sits above the sella turcica of the sphenoid bone, in a bony depression called the chiasmatic groove, just above the tuberculum sellae. It is immediately superior to the pituitary gland, which sits within the sella turcica itself.
In the optic chiasm the nasal/medial visual fields cross to the opposite side but the temporal/lateral visual fields do not. Optic tracts then form from the optic chiasm and pass to the lateral geniculate bodies of the thalamus. Optic radiations carry the information to the visual cortex of the occipital lobe for interpretation.