Oculomotor Nerve: Difference between revisions
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* Congenital | * Congenital | ||
* Idiopathic<ref>Modi P, Arsiwalla T. Cranial Nerve III Palsy. Available from:https://europepmc.org/article/NBK/nbk526112</ref> | * Idiopathic<ref>Modi P, Arsiwalla T. Cranial Nerve III Palsy. Available from:https://europepmc.org/article/NBK/nbk526112</ref> | ||
With unilateral third cranial nerve palsy (ie, oculomotor nerve palsy), the involved eye usually is deviated "down and out" (ie, infraducted and abducted), and there may be partial or complete ptosis. In addition, pupillary dilatation can cause anisocoria (greater in the light), symptomatic glare in bright light, and accommodation deficit that may cause blurred vision for near objects. A complete third nerve palsy presents with ipsilateral mydriasis, bilateral ptosis, contralateral elevation deficit, and ipsilateral adduction and depression deficits.<ref>Grover SK. Revisiting Third Nerve Palsy.DJO [serial online] 2020[cited 2021 Mar 31];31:18-22. Available from: https://www.djo.org.in/articles/31/1/Revisiting-Third-Nerve-Palsy.html</ref> | With unilateral third cranial nerve palsy (ie, oculomotor nerve palsy), the involved eye usually is deviated "down and out" (ie, infraducted and abducted), and there may be partial or complete ptosis. In addition, pupillary dilatation can cause anisocoria (greater in the light), symptomatic glare in bright light, and accommodation deficit that may cause blurred vision for near objects.<ref>James G, Andrew GL. Third Nerve Palsy (Oculomotor Nerve Palsy) Treatment & Management. E_Medicine.</ref> A complete third nerve palsy presents with ipsilateral mydriasis, bilateral ptosis, contralateral elevation deficit, and ipsilateral adduction and depression deficits.<ref>Grover SK. Revisiting Third Nerve Palsy.DJO [serial online] 2020[cited 2021 Mar 31];31:18-22. Available from: https://www.djo.org.in/articles/31/1/Revisiting-Third-Nerve-Palsy.html</ref> | ||
== Assessment == | == Assessment == | ||
The oculomotor nerve is examined in conjunction with the abducens and trochlear nerves by testing the movements of the eye. The patient is asked to follow a point with their eyes (commonly the tip of a pen) without moving their head. The target is moved in an ‘H-shape’ and the patient is asked to report any blurring of vision or diplopia (double vision). | |||
== Treatment == | == Treatment == | ||
Revision as of 21:00, 31 March 2021
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Original Editor - Innocent Abugu
Top Contributors - Innocent Abugu, Uchechukwu Chukwuemeka, Kim Jackson, Vidya Acharya and Joseph Ayotunde Aderonmu
Description[edit | edit source]
The oculomotor nerve is the third cranial nerve (CNIII). It has somatic motor (general somatic efferent) and visceral motor (general visceral efferent-parasympathetic) functions.[1]
Root[edit | edit source]
It originates from the oculomotor nucleus and the Edinger-Westphal nucleus within the midbrain of the brainstem.
Branches[edit | edit source]
Superior branch innervates the superior rectus and the levator palpabrae superioris
Inferior branch innervates the medial rectus, inferior rectus and inferior oblique.
Function[edit | edit source]
Motor[edit | edit source]
The oculomotor nerve is the chief motor nerve to the ocular and extraocular muscles. [1] The oculomotor nerves send somatic motor fibres to all extraocular muscles, except the superior oblique and lateral rectus. The superior branch supplies the superior rectus which elevates the eyeball, and the levator palpabrae superioris which raises the upper eyelid.
The inferior branch innervates the medial rectus adducts the eyeball, the inferior rectus which depresses the eyeball and the inferior oblique which elevates, abducts and laterally rotates the eyeball. The superior oblique and the lateral rectus are supplied by the trochlear and abducens nerves respectively.
Parasympathetic[edit | edit source]
There are two primary functions of the autonomic parasympathetic (involuntary) oculomotor nerve. It constricts the pupil (miosis) by innervating the smooth muscle (sphincter pupillae) near the pupil. It also innervates the ciliary muscles.[2] The sphincter pupillae causes narrowing of the pupil in order to prevent diverging light rays from the corneal periphery creating a blurred image.[3] The ciliary muscle changes the shape of the lens during accomodation.
Sympathetic[edit | edit source]
The oculomotor nerve has no direct function, but sympathetic fibres run with the oculomotor nerve to innervate the superior tarsal muscle (helps to raise the eyelid).[4]
Clinical relevance[edit | edit source]
Damage to the oculomotor nerve or any of its branches could lead to oculomotor motor nerve palsy (Third nerve palsy). Some of the causes include:
- Vascular ischemia
- Trauma
- Intracranial neoplasm
- Hemorrhage
- Congenital
- Idiopathic[5]
With unilateral third cranial nerve palsy (ie, oculomotor nerve palsy), the involved eye usually is deviated "down and out" (ie, infraducted and abducted), and there may be partial or complete ptosis. In addition, pupillary dilatation can cause anisocoria (greater in the light), symptomatic glare in bright light, and accommodation deficit that may cause blurred vision for near objects.[6] A complete third nerve palsy presents with ipsilateral mydriasis, bilateral ptosis, contralateral elevation deficit, and ipsilateral adduction and depression deficits.[7]
Assessment[edit | edit source]
The oculomotor nerve is examined in conjunction with the abducens and trochlear nerves by testing the movements of the eye. The patient is asked to follow a point with their eyes (commonly the tip of a pen) without moving their head. The target is moved in an ‘H-shape’ and the patient is asked to report any blurring of vision or diplopia (double vision).
Treatment[edit | edit source]
Resources[edit | edit source]
References[edit | edit source]
- ↑ 1.0 1.1 Keith LM, Arthur FD, Anne MR. Clinically Oriented Anatomy.
- ↑ Joyce C, Le PH, Peterson DC. Neuroanatomy, Cranial Nerve 3 (Oculomotor). Available from: https://www.ncbi.nlm.nih.gov/books/NBK537126/
- ↑ Bloom J, Motlagh M, Czyz CN. Anatomy, Head and Neck, Eye Iris Sphincter Muscle. Available from:https://www.ncbi.nlm.nih.gov/books/NBK532252/
- ↑ Navin L. The Oculomotor Nerve (CN III). Available from:https://teachmeanatomy.info/head/cranial-nerves/oculomotor/
- ↑ Modi P, Arsiwalla T. Cranial Nerve III Palsy. Available from:https://europepmc.org/article/NBK/nbk526112
- ↑ James G, Andrew GL. Third Nerve Palsy (Oculomotor Nerve Palsy) Treatment & Management. E_Medicine.
- ↑ Grover SK. Revisiting Third Nerve Palsy.DJO [serial online] 2020[cited 2021 Mar 31];31:18-22. Available from: https://www.djo.org.in/articles/31/1/Revisiting-Third-Nerve-Palsy.html
