• Source: Inferior oblique muscle

The inferior oblique muscle or obliquus oculi inferior is a thin, narrow muscle placed near the anterior margin of the floor of the orbit. The inferior oblique is one of the extraocular muscles, and is attached to the maxillary bone (origin) and the posterior, inferior, lateral surface of the eye (insertion). The inferior oblique is innervated by the inferior branch of the oculomotor nerve.




Structure



The inferior oblique arises from the orbital surface of the maxilla, lateral to the lacrimal groove. Unlike the other extraocular muscles (recti and superior oblique), the inferior oblique muscle does not originate from the common tendinous ring (annulus of Zinn).
Passing lateralward, backward, and upward, between the inferior rectus and the floor of the orbit, and just underneath the lateral rectus muscle, the inferior oblique inserts onto the scleral surface between the inferior rectus and lateral rectus.
In humans, the muscle is about 35 mm long.




= Innervation

=
The inferior oblique is innervated by the inferior division of the oculomotor nerve (cranial nerve III).




Function



Its actions are extorsion, elevation and abduction of the eye.
Primary action is extorsion (external rotation); secondary action is elevation; tertiary action is abduction (i.e. it extorts the eye and moves it upward and outwards). The field of maximal inferior oblique elevation is in the adducted position.
The inferior oblique muscle is the only muscle that is capable of elevating the eye when it is in a fully adducted position.




Clinical significance


While commonly affected by palsies of the inferior division of the oculomotor nerve, isolated palsies of the inferior oblique (without affecting other functions of the oculomotor nerve) are quite rare.
"Overaction" of the inferior oblique muscle is a commonly observed component of childhood strabismus, particularly infantile esotropia and exotropia. Because true hyperinnervation is not usually present, this phenomenon is better termed "elevation in adduction".
Surgical procedures of the inferior oblique include: loosening (also known as recession see Strabismus surgery), myectomy, marginal myotomy, and denervation and extirpation. It is also encountered and identified in lower lid blepharoplasty surgeries.




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References


This article incorporates text in the public domain from page 1023 of the 20th edition of Gray's Anatomy (1918)




External links


Anatomy figure: 29:01-08 at Human Anatomy Online, SUNY Downstate Medical Center
lesson3 at The Anatomy Lesson by Wesley Norman (Georgetown University) (orbit5)
Image at childrenshospital.org

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