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| | The Optic Nerve |
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| [[Anatomy]] > [[Gray's Anatomy| Gray's Anatomy of the Human Body]] > IX. Neurology > 5b. The Optic Nerve
| | The optic nerve, also known as cranial nerve II, is a vital component of the human visual system. It is responsible for transmitting visual information from the retina to the brain. The optic nerve is a paired structure, with one nerve for each eye, and plays a crucial role in the sense of sight. |
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| [[Henry Gray]] (1821–1865). Anatomy of the Human Body. 1918.
| | ==Anatomy== |
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| =='''The Optic Nerve'''==
| | The optic nerve is composed of retinal ganglion cell axons and glial cells. It extends from the optic disc in the retina to the optic chiasm, where the nerve fibers partially cross. The optic nerve is approximately 4 cm in length and is divided into four segments: |
| '''(N. Opticus; Second Nerve)'''
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| The '''[[optic nerve]]''' (Fig. 773), or '''nerve of sight''' consists mainly of fibers derived from the [[ganglionic]] cells of the retina. These [[axons]] terminate in [[arborizations]] around the cells in the lateral [[geniculate]] body, [[pulvinar]], and superior [[colliculus]] which constitute the lower or primary visual centers.
| | * [[Intraocular segment]] |
| | * [[Intraorbital segment]] |
| | * [[Intracanalicular segment]] |
| | * [[Intracranial segment]] |
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| From the cells of the lateral geniculate body and the pulvinar fibers pass to the [[cortical]] visual center, situated in the [[cuneus]] and in the neighborhood of the [[calcarine fissure]]. A few fibers of the [[optic nerve]], of small caliber, pass from the primary centers to the [[retina]] and are supposed to govern chemical changes in the retina and also the movements of some of its elements (pigment cells and cones).
| | ===Intraocular Segment=== |
| | The intraocular segment is the portion of the optic nerve that is located within the eye. It begins at the optic disc, where the nerve fibers converge to exit the eye. This segment is crucial for the initial transmission of visual signals. |
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| There are also a few fine fibers, afferent fibers, extending from the retina to the brain, that are supposed to be concerned in [[Pupillary reflex|pupillary]] reflexes.
| | ===Intraorbital Segment=== |
| | The intraorbital segment is the part of the optic nerve that lies within the orbit. It is surrounded by a protective sheath and is responsible for carrying visual information from the eye to the optic canal. |
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| | ===Intracanalicular Segment=== |
| | The intracanalicular segment passes through the optic canal, a bony structure in the skull. This segment is vulnerable to injury due to its confined space. |
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| <center>http://www.wikimd.org/images/gray/large/image773.gif </center>
| | ===Intracranial Segment=== |
| | The intracranial segment is the final portion of the optic nerve, extending from the optic canal to the optic chiasm. At the chiasm, fibers from the nasal half of each retina cross to the opposite side, allowing for binocular vision. |
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| | ==Function== |
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| FIG. 773– The left optic nerve and the optic tracts. (''Picture From the Classic Gray's Anatomy'')
| | The primary function of the optic nerve is to transmit visual information from the retina to the brain. This information is processed in the [[visual cortex]] of the brain, allowing for the perception of images. The optic nerve is essential for vision, and any damage to it can result in visual impairment or blindness. |
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| The optic nerve is peculiar in that its fibers and ganglion cells are probably third in the series of [[neurons]] from the [[receptors]] to the brain. Consequently the optic nerve corresponds rather to a tract of fibers within the brain than to the other [[cranial nerves]]. Its fibers pass backward and medialward through the orbit and optic [[foramen]] to the optic [[commissure]] where they partially [[decussate]]. The mixed fibers from the two nerves are continued in the optic tracts, the
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| ==='''primary visual centers of the brain'''===
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| The orbital portion of the optic nerve is from 20 mm. to 30 mm. in length and has a slightly sinuous course to allow for movements of the eyeball. It is invested by an outer sheath of [[dura mater]] and an inner sheath from the [[arachnoid]] which are attached to the [[sclera]] around the area where the nerve fibers pierce the choroid and sclera of the bulb.
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| A little behind the bulb of the eye the central artery of the retina with its accompanying vein perforates the optic nerve, and runs within it to the retina. As the nerve enters the optic foramen its [[dural sheath]] becomes continuous with that lining the orbit and the optic foramen.
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| In the optic foramen the [[ophthalmic]] artery lies below and to its outer side. The intercranial portion of the optic nerve is about 10 mm. in length. The '''[[Optic Chiasma]]''' (''chiasma opticum''), somewhat quadrilateral in form, rests upon the [[tuberculum]] [[sellae]] and on the anterior part of the diaphragma sellae.
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| It is in relation, ''above'' with the lamina terminalis; ''behind'' with the tuber [[cinereum]]; on ''either side'' with the [[anterior]] perforated substance. Within the [[chiasma]], the optic nerves undergo a partial [[decussation]].
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| The fibers forming the medial part of each tract and [[posterior]] part of the chiasma have no connection with the optic nerves. They simply cross in the chiasma, and connect the medial [[Geniculate body|geniculate]] bodies of the two sides; they form the '''[[commissure]] of Gudden''' The remaining and principal part of the chiasma consists of two sets of fibers, crossed and uncrossed. | |
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| The '''[[crossed fibers]]''' which are the more numerous, occupy the central part of the chiasma, and pass from the optic nerve of one side to the optic tract of the other, decussating in the chiasma with similar fibers of the opposite optic nerve.
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| The '''[[uncrossed fibers]]''' occupy the lateral part of the chiasma, and pass from the nerve of one side into the tract of the same side.
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| | ==Clinical Significance== |
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| <center>http://www.wikimd.org/images/gray/large/image774.gif </center>
| | Damage to the optic nerve can occur due to various conditions, including: |
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| | * [[Glaucoma]] |
| | * [[Optic neuritis]] |
| | * [[Ischemic optic neuropathy]] |
| | * [[Trauma]] |
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| FIG. 774– Scheme showing central connections of the optic nerves and optic tracts. (''Picture From the Classic Gray's Anatomy'')
| | ===Glaucoma=== |
| | Glaucoma is a group of eye conditions that damage the optic nerve, often due to increased intraocular pressure. It is a leading cause of blindness worldwide. |
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| The crossed fibers of the optic nerve tend to occupy the medial side of the nerve and the uncrossed fibers the lateral side. In the optic tract, however, the fibers are much more intermingled.
| | ===Optic Neuritis=== |
| | Optic neuritis is an inflammation of the optic nerve, often associated with multiple sclerosis. It can cause sudden vision loss and pain. |
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| ===Optic Tract=== | | ===Ischemic Optic Neuropathy=== |
| The '''Optic Tract''' (Fig. 774), passes backward and outward from the optic [[chiasma]] over the tuber [[cinereum]] and anterior perforated space to the cerebral [[peduncle]] and winds obliquely across its under surface.
| | Ischemic optic neuropathy is a condition caused by insufficient blood flow to the optic nerve, leading to vision loss. |
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| Its fibers terminate in the lateral [[geniculate]] body, the [[pulvinar]] and the superior [[colliculus]]. It is adherent to the tuber [[cinereum]] and the cerebral peduncle as it passes over them. In the region of the lateral [[Geniculate body|geniculate]] body it splits into two bands.
| | ===Trauma=== |
| | Trauma to the head or orbit can result in optic nerve damage, potentially causing permanent vision loss. |
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| The medial and smaller one is a part of the commissure of Gudden and ends in the medial geniculate body. From its mode of development, and from its structure, the [[optic nerve]] must be regarded as a prolongation of the brain substance, rather than as an ordinary [[cerebrospinal]] nerve.
| | ==Diagnosis== |
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| As it passes from the brain it receives sheaths from the three cerebral membranes, a [[perineural]] sheath from the [[pia mater]], an intermediate sheath from the [[arachnoid]], and an outer sheath from the [[dura mater]], which is also connected with the [[periosteum]] as it passes through the optic [[foramen]].
| | Diagnosis of optic nerve disorders typically involves: |
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| These sheaths are separated from each other by cavities which communicate with the [[subdural]] and [[subarachnoid]] cavities respectively. The innermost or [[perineural]] sheath sends a process around the arteria centralis retinae into the interior of the nerve, and enters intimately into its structure.
| | * [[Ophthalmoscopy]] |
| | * [[Visual field testing]] |
| | * [[Optical coherence tomography]] |
| | * [[Magnetic resonance imaging]] |
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| '''Note 130''' A specimen of congenital absence of the optic chiasma is to be found in the Museum of the Westminister Hospital. See also Henle, ''[[Nervenlehre]]'' p. 393, ed. 2.
| | ==Treatment== |
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| ==Function==
| | Treatment for optic nerve disorders depends on the underlying cause. Options may include: |
| 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 (for example, when reading the lens adjusts to near vision.
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| The eye's [[Blind spot (vision)|blind spot]] is a result of the absence of [[Photoreceptor cell|photoreceptor]]s in the area of the [[retina]] where the [[optic nerve]] leaves the eye.<ref name="Vilensky" />
| | * Medications to reduce intraocular pressure |
| ==Additional images==
| | * Corticosteroids for inflammation |
| <gallery>
| | * Surgery in certain cases |
| File:MRI of human eye.jpg|MRI scan of human eye showing optic nerve.
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| File:Gray514.png|The [[ophthalmic artery]] derived from [[internal carotid artery]] and its branches. (optic nerve is yellow)
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| File:Gray682.png|Superficial dissection of brain-stem. Lateral view.
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| File:Gray683.png|Dissection of brain-stem. Lateral view.
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| File:Gray722.svg|Scheme showing central connections of the optic nerves and optic tracts.
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| File:Gray776.png|Nerves of the orbit. Seen from above.
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| File:Gray777.png|Nerves of the orbit, and the ciliary ganglion. Side view.
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| File:Gray880.png|The terminal portion of the optic nerve and its entrance into the eyeball, in horizontal section.
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| File:Three Main Layers of the Eye.png|Structures of the eye labeled
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| File:Three Internal chambers of the Eye.png|This image shows another labeled view of the structures of the eye
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| File:Slide17ior.JPG|Optic nerve.Deep dissection.Inferior view.
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| File:Slide18ior.JPG|Optic nerve.Deep dissection.Inferior view.
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| File:Optic nerve.jpg|Optic nerve
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| File:Cranial endobasis of a 19-20 weeks foetus.JPG|Optic nerve
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| File:Human brain dura mater (reflections) description.JPG|Human brain dura mater (reflections)
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| File:Slide1dd.JPG|Optic nerve
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| File:Slide5ee.JPG|Optic nerve
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| File:Slide6uu.JPG|Optic nerve
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| File:Slide3PIT.JPG|Cerebrum.Inferior view.Deep dissection
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| File:Slide2HOM.JPG|Cerebral peduncle, optic chasm, cerebral aqueduct. Inferior view. Deep dissection.
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| </gallery>
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| ==External links== | | ==See Also== |
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| *[http://www.med.harvard.edu/AANLIB/cases/caseM/mr1_t/023.html The optic nerve on MRI] | | * [[Visual system]] |
| *{{BrainMaps|optic%20nerve}} | | * [[Retina]] |
| *[http://www.ifond.org/projects.php3 IFOND]
| | * [[Cranial nerves]] |
| *[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. | |
| *[http://www.liv.ac.uk/~rbj/RBJ/rbjteaching/Oculomotors.htm Animations of extraocular cranial nerve and muscle function and damage (University of Liverpool)]
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| *{{NormanAnatomy|lesson3}} ({{NormanAnatomyFig|orbit4}})
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| *{{NormanAnatomy|cranialnerves}} ({{NormanAnatomyFig|II}})
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| {{Cranial nerves}} | | {{Cranial nerves}} |
| {{Visual system}} | | {{Visual system}} |
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| {{Authority control}}
| | [[Category:Ophthalmology]] |
| | | [[Category:Neuroscience]] |
| [[Category:Optic nerve| ]] | | [[Category:Anatomy]] |
| [[Category:Visual system]] | |
| [[Category:Cranial nerves]] | |
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| {{grays}}
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| <references />
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The Optic Nerve
The optic nerve, also known as cranial nerve II, is a vital component of the human visual system. It is responsible for transmitting visual information from the retina to the brain. The optic nerve is a paired structure, with one nerve for each eye, and plays a crucial role in the sense of sight.
Anatomy
The optic nerve is composed of retinal ganglion cell axons and glial cells. It extends from the optic disc in the retina to the optic chiasm, where the nerve fibers partially cross. The optic nerve is approximately 4 cm in length and is divided into four segments:
Intraocular Segment
The intraocular segment is the portion of the optic nerve that is located within the eye. It begins at the optic disc, where the nerve fibers converge to exit the eye. This segment is crucial for the initial transmission of visual signals.
Intraorbital Segment
The intraorbital segment is the part of the optic nerve that lies within the orbit. It is surrounded by a protective sheath and is responsible for carrying visual information from the eye to the optic canal.
Intracanalicular Segment
The intracanalicular segment passes through the optic canal, a bony structure in the skull. This segment is vulnerable to injury due to its confined space.
Intracranial Segment
The intracranial segment is the final portion of the optic nerve, extending from the optic canal to the optic chiasm. At the chiasm, fibers from the nasal half of each retina cross to the opposite side, allowing for binocular vision.
Function
The primary function of the optic nerve is to transmit visual information from the retina to the brain. This information is processed in the visual cortex of the brain, allowing for the perception of images. The optic nerve is essential for vision, and any damage to it can result in visual impairment or blindness.
Clinical Significance
Damage to the optic nerve can occur due to various conditions, including:
Glaucoma
Glaucoma is a group of eye conditions that damage the optic nerve, often due to increased intraocular pressure. It is a leading cause of blindness worldwide.
Optic Neuritis
Optic neuritis is an inflammation of the optic nerve, often associated with multiple sclerosis. It can cause sudden vision loss and pain.
Ischemic Optic Neuropathy
Ischemic optic neuropathy is a condition caused by insufficient blood flow to the optic nerve, leading to vision loss.
Trauma
Trauma to the head or orbit can result in optic nerve damage, potentially causing permanent vision loss.
Diagnosis
Diagnosis of optic nerve disorders typically involves:
Treatment
Treatment for optic nerve disorders depends on the underlying cause. Options may include:
- Medications to reduce intraocular pressure
- Corticosteroids for inflammation
- Surgery in certain cases
See Also
