Optic nerve
- Optic Nerve is also a comic by the American cartoonist Adrian Tomine.
The optic nerve is the second of twelve paired cranial nerves but is usually considered to be part of the central nervous system as it is derived from an outpouching of the diencephalon during development. It consists mainly of nerve fibers extending from the retina to the primary visual centre.
The optic nerve arises from ganglionic cells of the eye's retina. Its axons terminate in the lateral geniculate nucleus from where information is relayed to the visual cortex and superior colliculus from where spinotectal reflexes are mediated.
The optic nerve leaves the orbit (eye) via the optic canal, running postero-medially towards the optic chiasm where there is a decussation (crossing) of fibres from the temporal visual fields of both eyes.
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.
The optic nerve contains roughly one million nerve fibers. This number is low compared to the roughly 130 million receptors in the retina, and implies that substantial pre-processing takes place in the retina before the signals are sent to the brain through the optic nerve.
The blind spot of the eye lies in the part of the retina where the optic nerve leaves the eye. This is because there are no photoreceptors in this area.
Damage to the optic nerve typically causes an abnormal pupillary reflex and loss of vision. The type of visual field loss will depend on which optic nerve was damaged and where the damage occurred.
