Optic nerve 152465 219172440 2008-06-13T22:19:31Z Gerbrant 190376 /* Physiology */ rm OR {{Infobox Nerve | Name = Optic Nerve| Latin = nervus opticus | GraySubject = 197 | GrayPage = 882 | Image = Gray773.png | Caption = The left optic nerve and the [[optic tract]]s. | Caption2 = Optic nerve leaving the back of a calf eye (from dissection).| Innervates = | BranchFrom = | BranchTo = | MeshName = Optic+Nerve | MeshNumber = A08.800.800.120.680 | }} {{about|the anatomical structure|the comic book series|Optic Nerve (comic)}} {{about||[[David Wojnarowicz]]|Optic Nerve (CD-ROM)}} The '''optic nerve''', also called '''cranial nerve II''', is the [[nerve]] that transmits visual information from the [[retina]] to the [[brain]]. ==Anatomy== The optic nerve is the second of twelve paired [[cranial nerve]]s but is considered to be part of the [[central nervous system]] as it is derived from an outpouching of the [[diencephalon]] during embryonic development. Consequently, the fibers are covered with myelin produced by [[oligodendrocyte]]s rather than the [[Schwann cell]]s of the [[peripheral nervous system]]. Similarly, the optic nerve is ensheathed in all three [[meninges|meningeal]] layers ([[dura mater|dura]], [[arachnoid mater|arachnoid]], and [[pia mater]]) rather than the [[epineurium]], [[perineurium]], and [[endoneurium]] found in peripheral nerves. This is an important issue, as fiber tracks of the mammalian central nervous system (as opposed to the peripheral nervous system) are incapable of regeneration and hence optic nerve damage produces irreversible blindness. The fibers from the [[retina]] run along the optic nerve to nine primary visual nuclei in the brain, whence a major relay inputs into the [[primary visual cortex]]. The optic nerve is composed of [[retina]]l [[ganglion cell]] axons and Portort cells. It leaves the [[Orbit (anatomy)|orbit]] (eye) via the [[optic canal]], running postero-medially towards the [[optic chiasm]] where there is a partial decussation (crossing) of fibers from the [[temporal]] visual fields of both eyes. Most of the [[axon]]s of the optic nerve terminate in the [[lateral geniculate nucleus]] from where information is relayed to the visual cortex. 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 fibres terminate in the lateral geniculate body. 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. ==Physiology== The eye's [[Blind spot (vision)|blind spot]] is a result of the absence of retina where the optic nerve leaves the eye. This is because there are no [[photoreceptor]]s in this area. The optic nerve contains 1.2 million nerve fibers. This number is low compared to the roughly 100 million photoreceptors in the retina.<ref>Jonas JB, Schneider U, Naumann GOH (1992) Count and density of human retinal photoreceptors. ''Graefe's Arch Clin Exp Ophthalmol'' 230:505-510.</ref> ==Role in disease== {{main|List of eye diseases and disorders}} Damage to the optic nerve typically causes permanent and potentially severe loss of [[Visual perception|vision]], as well as an abnormal [[Pupil constriction|pupillary reflex]], which is diagnostically important. The type of [[visual field]] loss will depend on which portions of the optic nerve were damaged. Generally speaking: * Damage ''before'' the optic chiasm causes loss of vision in the visual field of the same side only. * Damage ''in'' the chiasm causes loss of vision laterally in both visual fields ([[bitemporal hemianopia]]). It may occur in large [[pituitary adenoma]]ta. * Damage ''after'' the chiasm causes loss of vision on one side but affecting both visual fields: the visual field affected is located on the opposite side of the lesion. 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 tumors 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 cell]]s causing [[optic atrophy|optic neuropathy]] in a pattern of [[peripheral vision]] loss, initially sparing central vision. [[Optic neuritis]] is inflammation of the optic nerve. It is associated with a number of diseases, most notably [[multiple sclerosis]]. [[Anterior Ischemic Optic Neuropathy]] is a particular type of infarct that affects patients with an anatomical predisposition and cardiovascular risk factors. [[Ophthalmologist]]s, particularly those sub specialists who are [[neuro-ophthalmologist]]s, are often best suited to diagnose and treat diseases of the optic nerve. The International Foundation for Optic Nerve Diseases [[IFOND]] sponsors research and information on a variety of optic nerve disorders and may provide general direction. ==Additional images== <gallery> Image:MRI_of_human_eye.jpg|MRI scan of human eye showing optic nerve. Image:Gray514.png|The [[ophthalmic artery]] and its branches. (optic nerve is yellow) Image:Gray567.png|Dura mater and its processes exposed by removing part of the right half of the skull, and the brain. Image:Gray569.png|Tentorium cerebelli from above. Image:Gray682.png|Superficial dissection of brain-stem. Lateral view. Image:Gray683.png|Dissection of brain-stem. Lateral view. Image:Gray715.png|Mesal aspect of a brain sectioned in the median sagittal plane. Image:Gray722.png|Scheme showing central connections of the optic nerves and optic tracts. Image:Gray748.png|The fornix and [[corpus callosum]] from below. Image:Gray776.png|Nerves of the orbit. Seen from above. Image:Gray777.png|Nerves of the orbit, and the ciliary ganglion. Side view. Image:Gray873.png|The arteries of the choroid and iris. The greater part of the sclera has been removed. Image:Gray874.png|The veins of the choroid. Image:Gray880.png|The terminal portion of the optic nerve and its entrance into the eyeball, in horizontal section. Image:Human brain dura mater (reflections) description.JPG|Human brain dura mater (reflections) </gallery> == References == <references/> ==External links== * [http://www.med.harvard.edu/AANLIB/cases/caseM/mr1_t/023.html The optic nerve on MRI] * {{BrainMaps|optic%20nerve}} * [http://www.ifond.org/projects.php3 IFOND] * [http://fiteyes.com/blogs/dave/ online case history] - Optic nerve analysis with both scanning laser polarimetry with variable corneal compensation (GDx VCC) and confocal scanning laser ophthalmoscopy (HRT II - Heidelberg Retina Tomograph). Also includes actual fundus photos. * {{NormanAnatomy|lesson3}} ({{NormanAnatomyFig|orbit4}}) * {{NormanAnatomy|cranialnerves}} ({{NormanAnatomyFig|II}}) {{Cranial nerves}} {{Visual_system}} [[Category:Visual system]] [[Category:Cranial nerves]] [[ar:عصب بصري]] [[ca:Nervi òptic]] [[da:Synsnerve]] [[de:Sehnerv]] [[es:Nervio óptico]] [[eu:Nerbio optiko]] [[fr:Nerf optique]] [[it:Nervo ottico]] [[lt:Regos nervas]] [[nl:Nervus opticus]] [[ja:視神経]] [[no:Nervus opticus]] [[pl:Nerw wzrokowy]] [[pt:Nervo óptico]] [[ru:Зрительный нерв]] [[sr:Видни живац]] [[fi:Näköhermo]] [[sv:Synnerv]] [[tr:Nervus opticus]]