Cranial nerve II : the Optic nerve

The 2nd cranial nerve is the optic nerve. It is a sensory nerve that is responsible for vision.

40mm long, with a diameter of 4mm, the optic nerve is made up of 1200000 but unlike the peripheral nerves, the optic nerve is not able to regenerate.

Its damage can cause the partial or total loss of the eye on the side of the affected nerve. Many pathologies can affect the optic nerve (arteriosclerosis, multiple sclerosis, etc.).

The optic nerve originates from the anterolateral angle of the optic chiasm.

In the middle cranial fossa, the optic nerve travels through the optic chiasma cistern:

• Above: the anterior cerebralartery and vein
• Below: is located
  • the anterior part of the diaphragm of the saddle,
  • the optical splint
  • theophthalmic artery
• Laterally: theinternal carotid artery

In the optic canal, the optic nerve travels with theoptalmic artery located at the bottom and laterally of it.

In the orbit, the optic nerve occupies the axis of the musculofacial cone of the bulb and is located in the middle of the adipose body of the orbit. At this level it is enveloped by 3 sheaths which correspond to the extension of the meninges.

• Laterally : we find
  • theophthalmic artery, which will then pass above the optic nerve, surrounded by the posterior ciliary arteries.
  • the ciliary ganglion
  • the long ciliary nerves which are also located on the medial side
• Above and below: the ophthalmic veins

The optic nerve penetrates the eyeball and into and slightly below the posterior part of the eye.

The vascularization of the optic nerve is made possible by

• a superficial network that originates from the posterior short ciliary arteries
• a network of thecentral retinal artery.

The veins of the optic nerve drain into the central vein of the retina, which in turn drains into the cavernous sinus.

Here below, the main vision disorders:

Optic nerve damage results in blindness homolateral to the affected nerve and loss of the pupillary photomotor reflex.

For example, a lesion of the left optic nerve will cause blindness on the left side

This lesion causes a bitemporal hemianopia:

A lateral lesion of the optic chiasma will cause a homonymous nasal hemianopia, i.e. a lesion on the left will cause a left nasal hemianopia.

This results in 2 hemianopsias: homolateral temporal and contralateral nasal.

Example below for a lesion on the left:

It causes two upper quadrantanopsias: homolateral nasal and contralateral temporal.

Example below for a lesion on the left:

It causes two inferior quadrantanopsias: homolateral nasal and contralateral temporal.

Example below for a lesion on the left:

This lesion causes the appearance of a central scotoma and a decrease in visual acuity. A lesion on the right will cause a scotoma on the right

Marie Messager
Osteopath in Versailles Chantiers
78 - Yvelines