Optic nerve - wikipedia Optic nerve For other uses, see Optic Nerve. Optic Nerve The left optic nerve and the optic tracts. Details Identifiers Latin nervus opticus MeSH A08. 800.800. 120.680 TA A14. 2.01. 006 A15. 2.04. 024 FMA 50863 Anatomical terms of neuroanatomy ( edit on Wikidata ) Cranial nerves CN 0 -- Terminal CN I -- Olfactory CN II -- Optic CN III -- Oculomotor CN IV -- Trochlear CN V -- Trigeminal CN VI -- Abducens CN VII -- Facial CN VIII -- Vestibulocochlear CN IX -- Glossopharyngeal CN X -- Vagus CN XI -- Accessory CN XII -- Hypoglossal Overview Table The optic nerve, also known as cranial nerve II, is a paired nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived from optic stalks during the seventh week of development and is composed of retinal ganglion cell axons and glial cells ; it extends from the optic disc to the optic chiasma and continues as the optic tract to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus. Contents 1 Structure 2 Function 3 Clinical significance 3.1 Disease 4 Regeneration 5 Additional images 6 See also 7 References 8 External links Structure The optic nerve is the second of twelve paired cranial nerves and is technically part of the central nervous system, rather than the peripheral nervous system because it is derived from an out - pouching of the diencephalon ( optic stalks ) during embryonic development. As a consequence, the fibers of the optic nerve are covered with myelin produced by oligodendrocytes, rather than Schwann cells of the peripheral nervous system, and are encased within the meninges. Peripheral neuropathies like Guillain -- Barré syndrome do not affect the optic nerve. However, most typically the optic nerve is grouped with the other eleven cranial nerves and considered to be part of the peripheral nervous system. Dissection of Optic Nerve from above showing parts. Courtesy Dr. John B. Selhorst The optic nerve is ensheathed in all three meningeal layers ( dura, arachnoid, and pia mater ) rather than the epineurium, perineurium, and endoneurium found in peripheral nerves. Fiber tracts 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 fibres 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. A fundus photograph showing the back of the retina. The white circle is the beginning of the optical nerve. The optic nerve is composed of retinal ganglion cell axons and glial cells. 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, which has high acuity, these ganglion cells connect to as few as 5 photoreceptor cells ; in other areas of retina, they connect to many thousand 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 fibres from the temporal visual fields ( 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. Most of the axons 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 nucleus and are involved in reflexive eye movements. Other axons terminate in the suprachiasmatic nucleus and are involved in regulating the sleep - wake cycle. 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. Based on this anatomy, the optic nerve may be divided in the 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 fissure in the occipital lobe, and fibers carrying information from the contralateral inferior visual field terminate more superiorly, to the cuneus. Function The optic nerve transmits all visual information including brightness perception, color perception and contrast ( visual acuity ). It also conducts the visual impulses that are responsible for two important neurological reflexes : the light reflex and the accommodation reflex. The light reflex refers to the constriction of both pupils that occurs when light is shone into either eye ; the accommodation reflex refers to the swelling of the lens of eye that occurs when one looks at a near object as in reading ( lens adjusts to near vision ). 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. Clinical significance Disease Main article : List of eye diseases and disorders Damage to the optic nerve typically causes permanent and potentially severe loss of vision, as well as an abnormal pupillary reflex, which is diagnostically important. The type of visual field loss will depend on which portions of the optic nerve were damaged. In general : Damage to the optic nerve anterior to the optic chiasm causes loss of vision in the eye on the same side as the damage. Damage at the optic chiasm typically causes loss of vision laterally in both visual fields ( bitemporal hemianopsia ). It may occur with large pituitary tumors pituitary adenoma. ( see image on right of Paris seen with bitemporal hemianopsia ) Paris views showing vision with loss of both temporal visual fields Damage to the optic tract, which is behind ( posterior ) to the chiasm, causes loss of the entire visual field from the side opposite the damage ( so if the left optic tract is cut, there is 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 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 cells causing optic neuropathy in a pattern of peripheral vision loss, initially sparing central vision. Glaucoma is associated with increased intraocular pressure that damages the optic nerve as it exits the eyeball. Although glaucoma does eventually damage the optic nerve, it is primarily a disease of eye not of the nerve. 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 `` stroke of the optic nerve '' and affects the optic nerve head. There is usually a sudden loss of blood supply and nutrients to the optic nerve head ( where the nerve exits the eyeball ). 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. 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 ( swelling of blood vessels ) 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 Ophthalmologists and optometrists 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. Regeneration Similar to other CNS tracts, the optic has very limited regenerative potential after injury. However, some new techniques are being developed to increase this potential. Additional images MRI scan of human eye showing optic nerve. The ophthalmic artery and its branches. ( optic nerve is yellow ) Superficial dissection of brain - stem. Lateral view. Dissection of brain - stem. Lateral view. Scheme showing central connections of the optic nerves and optic tracts. Nerves of the orbit. Seen from above. Nerves of the orbit, and the ciliary ganglion. Side view. The terminal portion of the optic nerve and its entrance into the eyeball, in horizontal section. Structures of the eye labeled This image shows another labeled view of the structures of the eye Optic nerve. Deep dissection. Inferior view. Optic nerve. Deep dissection. Inferior view. Optic nerve Optic nerve Human brain dura mater ( reflections ) Optic nerve Optic nerve Optic nerve Cerebrum. Inferior view. Deep dissection Cerebral peduncle, optic chasm, cerebral aqueduct. Inferior view. Deep dissection. See also Wikimedia Commons has media related to Optic nerve. This article uses anatomical terminology ; for an overview, see Anatomical terminology. Cranial nerve References ^ Jump up to : Vilensky, Joel ; Robertson, Wendy ; Suarez - Quian, Carlos ( 2015 ). The Clinical Anatomy of the Cranial Nerves : The Nerves of `` On Olympus Towering Top ''. Ames, Iowa : Wiley - Blackwell. ISBN 978 - 1118492017. ^ Jump up to : Selhorst, JB ; Chen, Y ( 2009 ). `` The Optic Nerve ''. Seminars in Neurology. 29 : 29 -- 35. Jump up ^ Jonas, Jost B. ; et al. ( May 1992 ). `` Human optic nerve fiber count and optic disc size ''. Investigative Ophthalmology & Visual Science. 33 ( 6 ). Jump up ^ Textbook of Veterinary Anatomy, 4th Edition. Dyce, Sack and Wensing Jump up ^ `` Glaucoma and Retinal Neurodegenerative Research Group ''. www.ucl.ac.uk. External links The optic nerve on MRI Stained brain slice images which include the `` optic % 20nerve '' at the BrainMaps project IFOND 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. Animations of extraocular cranial nerve and muscle function and damage ( University of Liverpool ) lesson3 at The Anatomy Lesson by Wesley Norman ( Georgetown University ) ( orbit4 ) cranialnerves at The Anatomy Lesson by Wesley Norman ( Georgetown University ) ( II ) Notes on Optic Nerve The cranial nerves terminal Nuclei Septal nuclei Course no significant branches olfactory Nuclei Anterior olfactory nucleus Course olfactory bulb olfactory tract optic Nuclei Lateral geniculate nucleus Course optic chiasm optic tract oculomotor Nuclei Oculomotor nucleus Edinger -- Westphal nucleus Branches superior parasympathetic root of ciliary ganglion / ciliary ganglion inferior trochlear Nucleus Branches no significant branches trigeminal Nuclei PSN Spinal trigeminal nucleus MN TMN Course trigeminal ganglion Branches ophthalmic maxillary mandibular abducens Nucleus Branches no significant branches facial near origin intermediate nerve geniculate inside facial canal greater petrosal pterygopalatine ganglion nerve to the stapedius chorda tympani lingual nerve submandibular ganglion at stylomastoid foramen posterior auricular suprahyoid digastric stylohyoid parotid plexus temporal zygomatic buccal mandibular cervical Nuclei Facial motor nucleus Solitary nucleus Superior salivary nucleus vestibulocochlear Nuclei Vestibular nuclei Cochlear nuclei cochlear nerve striae medullares lateral lemniscus vestibular Scarpa 's ganglion glossopharyngeal before jugular fossa ganglia superior inferior after jugular fossa tympanic tympanic plexus lesser petrosal otic ganglion stylopharyngeal branch pharyngeal branches tonsillar branches lingual branches carotid sinus Nuclei Nucleus ambiguus Inferior salivatory nucleus Solitary nucleus vagus before jugular fossa ganglia superior inferior after jugular fossa meningeal branch auricular branch neck pharyngeal branch pharyngeal plexus superior laryngeal external internal recurrent laryngeal ( inferior ) superior cervical cardiac thorax inferior cardiac pulmonary vagal trunks anterior posterior abdomen celiac renal hepatic anterior gastric posterior gastric Nuclei Nucleus ambiguus Dorsal nucleus of vagus nerve Solitary nucleus accessory Nuclei Nucleus ambiguus Spinal accessory nucleus cranial spinal hypoglossal Nucleus Branches lingual Optical illusions List of optical illusions Afterimage Barberpole Bezold Blivet Café wall Cornsweet Delboeuf Ebbinghaus Ehrenstein Flash lag Fraser spiral Grid Hering Jastrow Mach McCollough Müller - Lyer Necker Orbison Penrose stairs triangle Peripheral drift Poggendorff Ponzo Rubin Sander Schroeder Ternus Vertical -- horizontal White 's Wundt Zöllner Related Auditory Tactile Temporal Op art Ascending and Descending Waterfall GND : 4205981 - 1 NDL : 00571252 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Optic_nerve&oldid=804841103 '' Categories : Optic nerve Visual system Cranial nerves Hidden categories : Medicine infobox template using GraySubject or GrayPage All articles with unsourced statements Articles with unsourced statements from March 2016 Wikipedia articles with GND identifiers Talk Contents About Wikipedia Azərbaycanca Bân - lâm - gú Български Bosanski Català Čeština Dansk Deutsch Eesti Ελληνικά Español Euskara فارسی Français Galego 한국어 Հայերեն हिन्दी Hrvatski Bahasa Indonesia Italiano עברית Қазақша Latina Lietuvių Magyar Nederlands 日本 語 Norsk Polski Português Română Русский Simple English Српски / srpski Srpskohrvatski / српскохрватски Suomi Svenska Татарча / tatarça తెలుగు ไทย Türkçe Українська 中文 Edit links This page was last edited on 11 October 2017, at 13 : 22. 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Question: where does the optic nerve enter the eye
Answer: via the optic canal