Optic nerve

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The optic nerveis the second (CN II) cranial nerve (TA: nervus opticus or nervus cranialis II). It is a purely sensory nerve that conveys visual information from the eye to the brain.

The nerve arises from the back of the globe exiting the orbit via the optic canal. It joins the contralateral optic nerve at the optic chiasm where medial fibres decussate before continuing as the optic tracts.

The cells of origin consist of the ganglion cells of the retina with the main central connections consisting of the lateral geniculate nucleus of the thalamus, ~~and~~and the pretectal area of the midbrain.

Gross anatomy

Similar to the olfactory nerve (CN I), the optic nerve is really an extension of the central nervous system. It is not surrounded by Schwann cells with the first sensory bipolar cell body located peripherally in the retina. Their central processes synapse on ganglion cells on the vitreous surface of the retina and their central processes pass via the optic disc out of the globe and form the optic nerve proper. The optic nerve is traditionally divided into four segments:

Intraocular segment

Formed from nerve fibres of the retina and emerges through an opening in the sclera known as the lamina cribrosa.

Intraorbital segment

Passes posteriorly and centrally within the orbit and is surrounded by dural lining and CSF; hence it directly communicates with the subarachnoid space and therefore allows transmission of increased pressure from hydrocephalus to manifest as papilloedema; additionally, the dural covering can develop a meningioma.

Intracanalicular segment

Where the optic nerve exits through the tendinous ring and optic canal superior to the ophthalmic artery.

Intracranial segment

Also known as the cisternal segment, enters the middle cranial fossa and passes within the suprasellar cistern with the anterior cerebral artery at its superolateral aspect joining the contralateral optic nerve at the optic chiasm.

At the optic chiasm, the nasal fibres of each optic nerve (fibres carrying light impulses from the nasal side of the retina) decussate while the temporal fibres do not (partial decussation). From the optic chiasm arise two optic tracts, each one containing nasal fibres of the contralateral optic nerve and temporal fibres from the ipsilateral optic nerve. The optic tract courses around the cerebral peduncle to relay in the lateral geniculate body of the thalamus.

Arterial supply

Intraocular, intraorbital, and intracanalicular segments are supplied by the ophthalmic artery and its branch, the central retinal artery.

Small branches of the anterior cerebral artery (ACA) and the superior hypophyseal artery supply the intracranial segment of the optic nerves and optic chiasm.

The optic tracts are supplied by small branches of the anterior choroidal and PCOM arteries.

Variant anatomy

According to a study by Delano et al., the course of the optic nerve in relation to the sphenoid sinus ~~was~~can be classified according to four types ⁶:

type 1: most common (76%): the optic nerve is immediately adjacent to the lateral or superior wall of the sphenoidal sinus, without impression on the sinus wall
type 2: (15%): nerve causes an impression on the lateral sphenoidal sinus wall
type 3: (6%): nerve courses through the sphenoidal sinus rather than simply running adjacent to the sinus
type 4: (3%) nerve courses immediately lateral to the posterior ethmoidal and sphenoidal sinuses

Related pathology

-<p>The <strong>optic nerve </strong>is the second (<strong>CN II</strong>) <a href="/articles/cranial-nerves">cranial nerve</a>. It is a purely sensory nerve that conveys visual information from the eye to the brain. </p><p>The nerve arises from the back of the globe exiting the orbit via the <a href="/articles/optic-canal">optic canal</a>. It joins the contralateral optic nerve at the <a href="/articles/optic-chiasm">optic chiasm</a> where medial fibres decussate before continuing as the <a href="/articles/optic-tract">optic tracts</a>. </p><p>The cells of origin consist of the ganglion cells of the retina with the main central connections consisting of the lateral geniculate nucleus of the thalamus, and the pretectal area of the midbrain.</p><h4>Gross anatomy</h4><p>Similar to the <a href="/articles/olfactory-nerve">olfactory nerve (CN I)</a>, the optic nerve is really an extension of the <a href="/articles/neuroanatomy">central nervous system</a>. It is not surrounded by Schwann cells with the first sensory bipolar cell body located peripherally in the <a href="/articles/retina">retina</a>. Their central processes synapse on ganglion cells on the <a href="/articles/vitreous">vitreous</a> surface of the retina and their central processes pass via the optic disc out of the <a href="/articles/globe">globe</a> and form the optic nerve proper. The optic nerve is divided into four segments:</p><h5>Intraocular segment</h5><p>Formed from nerve fibres of the retina and emerges through an opening in the sclera known as the lamina cribrosa.</p><h5>Intraorbital segment</h5><p>Passes posteriorly and centrally within the orbit and is surrounded by dural lining and CSF; hence it directly communicates with the <a href="/articles/subarachnoid-space">subarachnoid space</a> and therefore allows transmission of increased pressure from <a href="/articles/hydrocephalus">hydrocephalus</a> to manifest as <a href="/articles/papilloedema">papilloedema</a>; additionally, the dural covering can develop a <a href="/articles/optic-nerve-sheath-meningioma">meningioma</a>.</p><h5>Intracanalicular segment</h5><p>Where the optic nerve exits through the <a href="/articles/tendinous-ring">tendinous ring</a> and <a href="/articles/optic-canal">optic canal</a> superior to the <a href="/articles/ophthalmic-artery">ophthalmic artery</a>.</p><h5>Intracranial segment</h5><p>Also known as the cisternal segment, enters the <a href="/articles/middle-cranial-fossa">middle cranial fossa</a> and passes within the suprasellar cistern with the <a href="/articles/anterior-cerebral-artery">anterior cerebral artery</a> at its superolateral aspect joining the contralateral optic nerve at the <a href="/articles/optic-chiasm">optic chiasm</a>.</p><p>At the optic chiasm, the nasal fibres of each optic nerve (fibres carrying light impulses from the nasal side of the retina) decussate while the temporal fibres do not (partial decussation). From the optic chiasm arise two <a href="/articles/optic-tract">optic tracts</a>, each one containing nasal fibres of the contralateral optic nerve and temporal fibres from the ipsilateral optic nerve. The optic tract courses around the cerebral peduncle to relay in the lateral geniculate body of the thalamus.</p><h4>Arterial supply</h4><p>Intraocular, intraorbital, and intracanalicular segments are supplied by the <a href="/articles/ophthalmic-artery">ophthalmic artery</a> and its branch, the <a href="/articles/central-artery-of-the-retina">central retinal artery</a>.</p><p>Small branches of the <a href="/articles/anterior-cerebral-artery">anterior cerebral artery (ACA)</a> and the <a href="/articles/superior-hypophyseal-artery">superior hypophyseal artery</a> supply the intracranial segment of the optic nerves and optic chiasm.</p><p>The optic tracts are supplied by small branches of the <a href="/articles/anterior-choroidal-artery">anterior choroidal</a> and <a href="/articles/posterior-communicating-artery">PCOM arteries</a>.</p><h4>Variant anatomy</h4><p>According to a study by Delano et al., the course of the optic nerve in relation to the <a href="/articles/sphenoid-sinus">sphenoid sinus</a> was classified according to four types <sup>6</sup>:</p><ul>
+<p>The <strong>optic nerve</strong><strong> </strong>is the <strong>second</strong> (<strong>CN II</strong>) <a href="/articles/cranial-nerves">cranial nerve</a> (<a href="/articles/terminologia-anatomica-1">TA</a>: nervus opticus or nervus cranialis II). It is a purely sensory nerve that conveys visual information from the <a href="/articles/ocular-globe-1">eye</a> to the <a href="/articles/brain">brain</a>. </p><p>The nerve arises from the back of the globe exiting the orbit via the <a href="/articles/optic-canal">optic canal</a>. It joins the contralateral optic nerve at the <a href="/articles/optic-chiasm">optic chiasm</a> where medial fibres decussate before continuing as the <a href="/articles/optic-tract">optic tracts</a>. </p><p>The cells of origin consist of the ganglion cells of the retina with the main central connections consisting of the lateral geniculate nucleus of the thalamus, and the pretectal area of the midbrain.</p><h4>Gross anatomy</h4><p>Similar to the <a href="/articles/olfactory-nerve">olfactory nerve (CN I)</a>, the optic nerve is really an extension of the <a href="/articles/neuroanatomy">central nervous system</a>. It is not surrounded by Schwann cells with the first sensory bipolar cell body located peripherally in the <a href="/articles/retina">retina</a>. Their central processes synapse on ganglion cells on the <a href="/articles/vitreous">vitreous</a> surface of the retina and their central processes pass via the optic disc out of the <a href="/articles/globe">globe</a> and form the optic nerve proper. The optic nerve is traditionally divided into four segments:</p><h5>Intraocular segment</h5><p>Formed from nerve fibres of the retina and emerges through an opening in the <a title="Sclera" href="/articles/sclera">sclera</a> known as the <a title="Lamina cribrosa sclerae" href="/articles/lamina-cribrosa-sclerae">lamina cribrosa</a>.</p><h5>Intraorbital segment</h5><p>Passes posteriorly and centrally within the orbit and is surrounded by dural lining and CSF; hence it directly communicates with the <a href="/articles/subarachnoid-space">subarachnoid space</a> and therefore allows transmission of increased pressure from <a href="/articles/hydrocephalus">hydrocephalus</a> to manifest as <a href="/articles/papilloedema">papilloedema</a>; additionally, the dural covering can develop a <a href="/articles/optic-nerve-sheath-meningioma">meningioma</a>.</p><h5>Intracanalicular segment</h5><p>Where the optic nerve exits through the <a href="/articles/tendinous-ring">tendinous ring</a> and <a href="/articles/optic-canal">optic canal</a> superior to the <a href="/articles/ophthalmic-artery">ophthalmic artery</a>.</p><h5>Intracranial segment</h5><p>Also known as the cisternal segment, enters the <a href="/articles/middle-cranial-fossa">middle cranial fossa</a> and passes within the suprasellar cistern with the <a href="/articles/anterior-cerebral-artery">anterior cerebral artery</a> at its superolateral aspect joining the contralateral optic nerve at the <a href="/articles/optic-chiasm">optic chiasm</a>.</p><p>At the optic chiasm, the nasal fibres of each optic nerve (fibres carrying light impulses from the nasal side of the retina) decussate while the temporal fibres do not (partial decussation). From the optic chiasm arise two <a href="/articles/optic-tract">optic tracts</a>, each one containing nasal fibres of the contralateral optic nerve and temporal fibres from the ipsilateral optic nerve. The optic tract courses around the cerebral peduncle to relay in the lateral geniculate body of the thalamus.</p><h4>Arterial supply</h4><p>Intraocular, intraorbital, and intracanalicular segments are supplied by the <a href="/articles/ophthalmic-artery">ophthalmic artery</a> and its branch, the <a href="/articles/central-artery-of-the-retina">central retinal artery</a>.</p><p>Small branches of the <a href="/articles/anterior-cerebral-artery">anterior cerebral artery (ACA)</a> and the <a href="/articles/superior-hypophyseal-artery">superior hypophyseal artery</a> supply the intracranial segment of the optic nerves and optic chiasm.</p><p>The optic tracts are supplied by small branches of the <a href="/articles/anterior-choroidal-artery">anterior choroidal</a> and <a href="/articles/posterior-communicating-artery">PCOM arteries</a>.</p><h4>Variant anatomy</h4><p>According to a study by Delano et al., the course of the optic nerve in relation to the <a href="/articles/sphenoid-sinus">sphenoid sinus</a> can be classified according to four types <sup>6</sup>:</p><ul>

References changed:

7. FIPAT. Terminologia Anatomica. 2nd Ed. FIPAT.library.dal.ca. Federative International Programme for Anatomical Terminology, 2019. <a href="https://fipat.library.dal.ca/TA2/">https://fipat.library.dal.ca/TA2/</a>

Updates to Synonym Attributes

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