Product Code Database
In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual system information from the retina to the brain. In humans, the optic nerve is derived from during the seventh week of development and is composed of retinal ganglion cell axons and ; it extends from the optic disc to the optic chiasma and continues as the optic tract to the lateral geniculate nucleus, Pretectal area, and superior colliculus. (2025). 9781118492017, Wiley-Blackwell. ISBN 9781118492017
The optic nerve is ensheathed in all three meningeal layers (dura mater, arachnoid mater, and pia mater) rather than the epineurium, perineurium, and endoneurium found in peripheral nerves. Nerve tract of the mammalian central nervous system have only limited regenerative capabilities compared to the peripheral nervous system. Therefore, in most mammals, optic Nerve injury results in irreversible blindness. The fibers from the retina run along the optic nerve to nine primary visual nuclei in the brain, from which a major relay inputs into the primary visual cortex.
The optic nerve is composed of retinal ganglion cell axons and glia. Each human optic nerve contains between 770,000 and 1.7 million nerve fibers, which are axons of the retinal ganglion cells of one retina. In the Fovea centralis, which has high acuity, these ganglion cells connect to as few as 5 photoreceptor cells; in other areas of the retina, they connect to thousands of photoreceptors.
The optic nerve leaves the orbit (eye socket) via the optic canal, running postero-medially towards the optic chiasm, where there is a partial decussation (crossing) of fibers from the temporal (the nasal hemi-retina) of both eyes. The proportion of decussating fibers varies between species, and is correlated with the degree of binocular vision enjoyed by a species.Textbook of Veterinary Anatomy, 4th Edition. Dyce, Sack and Wensing Most of the of the optic nerve terminate in the lateral geniculate nucleus from where information is relayed to the visual cortex, while other axons terminate in the pretectal area and are involved in reflexive . Other axons terminate in the suprachiasmatic nucleus and are involved in regulating the Circadian rhythm. 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 optic nerve component lengths are 1 mm in the globe, 24 mm in the orbit, 9 mm in the optic canal, and 16 mm 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.
Based on this anatomy, the optic nerve may be divided into four parts as indicated in the image at the top of this section (this view is from above as if you were looking into the orbit after the top of the skull had been removed): 1. the optic head (which is where it begins in the eyeball (globe) with fibers from the retina); 2. orbital part (which is the part within the orbit); 3. intracanicular part (which is the part within a bony canal known as the optic canal); and, 4. cranial part (the part within the cranial cavity, which ends at the optic chiasm).
From the lateral geniculate body, fibers of the optic radiation pass to the visual cortex in the occipital lobe of the brain. In more specific terms, fibers carrying information from the contralateral superior visual field traverse Meyer's loop to terminate in the lingual gyrus below the Calcarine sulcus in the occipital lobe, and fibers carrying information from the contralateral inferior visual field terminate more superiorly, to the cuneus.
The eye's blind spot is a result of the absence of photoreceptors in the area of the retina where the optic nerve leaves the eye.
The type of visual field loss will depend on which portions of the optic nerve were damaged. In general, the location of the damage in relation to the optic chiasm (see diagram above) will affect the areas of vision loss. Damage to the optic nerve that is anterior, or in front of the optic chiasm (toward the face) causes loss of vision in the eye on the same side as the damage. Damage at the optic chiasm itself typically causes loss of vision laterally in both visual fields or bitemporal hemianopsia (see image to the right). Such damage may occur with large pituitary tumors, such as pituitary adenoma. Finally, damage to the optic tract, which is posterior to, or behind the chiasm, causes loss of the entire visual field from the side opposite the damage, e.g. if the left optic tract were cut, there would be a loss of vision from the entire right visual field.
Injury to the optic nerve can be the result of congenital or inheritable problems like Leber's hereditary optic neuropathy, glaucoma, trauma, toxicity, inflammation, ischemia, infection (very rarely), or compression from or aneurysms. By far, the three most common injuries to the optic nerve are from glaucoma; optic neuritis, especially in those younger than 50 years of age; and anterior ischemic optic neuropathy, usually in those older than 50.
Glaucoma is a group of diseases involving loss of retinal ganglion cells causing optic atrophy in a pattern of peripheral vision loss, initially sparing central vision. Glaucoma is frequently associated with increased intraocular pressure that damages the optic nerve as it exits the eyeball. The trabecular meshwork assists the drainage of Aqueous humour fluid. The presence of excess aqueous humor, increases IOP, yielding the diagnosis and symptoms of glaucoma.
Optic neuritis is inflammation of the optic nerve. It is associated with a number of diseases, the most notable one being multiple sclerosis. The patient will likely experience varying vision loss and eye pain. The condition tends to be episodic.
Anterior ischemic optic neuropathy is commonly known as a "stroke of the optic nerve" and affects the optic nerve head (where the nerve exits the eyeball). There is usually a sudden loss of blood supply and nutrients to the optic nerve head. Vision loss is typically sudden and most commonly occurs upon waking up in the morning. This condition is most common in diabetic patients 40–70 years old.
Other optic nerve problems are less common. Optic nerve hypoplasia is the underdevelopment of the optic nerve resulting in little to no vision in the affected eye. Tumors, especially those of the pituitary gland, can put pressure on the optic nerve causing various forms of visual loss. Similarly, cerebral aneurysms, a swelling of Blood vessel, can also affect the nerve. Trauma can cause serious injury to the nerve. Direct optic nerve injury can occur from a penetrating injury to the orbit, but the nerve can also be injured by indirect trauma in which severe head impact or movement stretches or even tears the nerve.
and can detect and diagnose some optic nerve diseases but neuro-ophthalmologists are often best suited to diagnose and treat diseases of the optic nerve. The International Foundation for Optic Nerve Diseases (IFOND) sponsors research and provides information on a variety of optic nerve disorders.
==Additional images==
|
|
