Definitions

rectus inferior

Inferior oblique muscle

The Obliquus oculi inferior (inferior oblique) is a thin, narrow muscle, placed near the anterior margin of the floor of the orbit.

Action

Its actions are lateral rotation, elevation and abduction of the eye.

Primary action is extorsion; secondary action is elevation; tertiary action is abduction (i.e. it extorts the eye and moves it upward and outward). The field of maximal inferior oblique elevation is in the adducted position.

Path

It arises from the orbital surface of the maxilla, lateral to the lacrimal groove.

Passing lateralward, backward, and upward, between the inferior rectus and the floor of the orbit, the inferior oblique inserts onto the scleral surface between the inferior rectus and lateral rectus.

It is the only muscle of eye movement whose origin is not on the common tendonous ring (annulus of Zinn).

Innervation

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

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 (recession), myectomy, marginal myotomy, and denervation and extirpation.

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