The '''optic nerve''' is the second of twelve paired cranial nerves but is usually considered to be part of the central nervous system. 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 and superior colliculus.
The optic nerve leaves the orbit (eye) via the optic fissure, running postero-medially towards the optic chiasm where there is crossing of fibres from the temporal 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.
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 can cause loss of vision. The type of visual field loss will depend on which optic nerve was damaged and where the damage occurred.
Cranial nerves
External links
* http://www.med.harvard.edu/AANLIB/cases/caseM/mr1_t/023.html The optic nerve on MRI
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