anatomy of cranial nerve II

Last reviewed 01/2018

The optic nerve is purely sensory.

The origins of the optic nerve are the axons of the neurones in the ganglionic layer of the retina. These pass on the inner surface of the retina to the optic disc where they exit the eye covered by oligodendrocytic myelin sheaths and a connective tissue outer layer contiguous with the sclera.

The optic nerve leaves the orbital cavity via the optic foramen close to the ophthalamic artery. It then joins the nerve from the other side to form the optic chiasm. Here the spatial orientation of fibres from different parts of the fundus are preserved, i.e. fibres from the lower part of the retina are found in the inferior part of the chiasm and vice versa.

In the optic chiasm fibres from the nasal visual fields - the temporal retinal halves - do not cross, whereas fibres from the temporal visual fields - the nasal halves of the retinae - do cross. Some fibres leave the optic chiasm to finish in the superior colliculus and are responsible for the light reflex. The remainder of the fibres leave the optic chiasm in either of the optic tracts and are responsible for vision. Because of the crossing over of certain fibres in the optic chiasm, the right optic tract will carry information concerning vision in the right nasal visual field and the left temporal visual field. The opposite information is carried by the left optic tract. The fibres in each respective optic tract travel to their respective lateral geniculate body (LGN) in the thalamus.

From the LGN fibres travel via the optic radiation, passing through the posterior part of the internal capsule, to finish in the visual cortex of the occipital lobe. During their course, fibres serving the upper quadrants traverse the temporal lobe while those serving the lower quadrants pass through the parietal lobe.