Optic Nerve-Cranial Nerve II

The optic nerve is composed of retinal ganglion cell axons and support cells. It leaves the orbit (eye) via the optic canal, running postero-medially towards the optic chiasm where there is a partial decussation (crossing) of fibers from the temporal visual fields of both eyes. Most of the axons of the optic nerve terminate in the lateral geniculate nucleus from where information is relayed to the visual cortex. Its diameter increases from about 1.6 mm within the eye, to 3.5 mm in the orbit to 4.5 mm within the cranial space. (The precise dimensions of the optic nerve head are 1.5 mm (H) x 1.75 mm (V). The optic nerve component lengths are 1mm in the globe, 25mm in the orbit, 9mm in the optic canal and 16mm in the cranial space before joining the optic chiasm. There, partial decussation occurs and about 53% of the fibers cross to form the optic tracts. Most of these fibers terminate in the lateral geniculate body.
From the lateral geniculate body, fibers of the optic radiation pass to the visual cortex in the occipital lobe of the brain. More specifically, fibers carrying information from the contralateral superior visual field traverse Meyer's loop to terminate in the lingual gyrus below the calcarine fissure in the occipital lobe, and fibers carrying information from the contralateral inferior visual field terminate more superiorly.