Inferior oblique muscle

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.[1]

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.[2]

A montage of five pictures of the right eye of a male subject with partial heterochromia, demonstrating torsional eye movement

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".[3]

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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  Eye movement of lateral rectus muscle, superior view
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  Eye movement of medial rectus muscle, superior view
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  Eye movement of inferior rectus muscle, superior view
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  Eye movement of superior rectus muscle, superior view
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  Eye movement of superior oblique muscle, superior view
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  Eye movement of inferior oblique muscle, superior view
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  Anterior view

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  Dissection showing origins of right ocular muscles, and nerves entering by the superior orbital fissure.
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  Inferior oblique muscle
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  Extrinsic eye muscle. Nerves of orbita. Deep dissection.
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  Extrinsic eye muscle. Nerves of orbita. Deep dissection.

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

• 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