Extraocular muscles · 19 of 24
What does the inferior oblique do?
The inferior oblique is the only extraocular muscle that does not arise at the back of the orbit. It starts on the orbital floor just behind the rim, beside the lacrimal sac, runs back and out beneath the inferior rectus, and inserts on the outer back of the globe near the macula. It elevates the eye, most in adduction, and extorts and abducts it.
- Action
- Extorsion; also elevation (most in adduction) and abduction
- Purest test
- Looking up with the eye adducted
- Nerve
- Inferior division of the oculomotor nerve (CN III)
- Origin
- The orbital floor, anteromedially, near the nasolacrimal fossa
The partner of the superior oblique
The inferior oblique's line of pull mirrors the superior oblique's, from the front and medial side of the orbit to the back of the globe, but from below. So where the superior oblique intorts and depresses, the inferior oblique extorts and elevates. Its elevation is strongest in adduction, and in upgaze it works with the superior rectus of the same eye and with the superior rectus of the other eye.
Overaction
The inferior oblique is more often too strong than too weak. When the superior oblique is palsied its antagonist overacts and the affected eye shoots upwards on adduction, the sign that makes a fourth nerve palsy visible across a room. Primary inferior oblique overaction accompanies childhood esotropia and gives a V pattern, where the eyes diverge more in upgaze. Both are treated by weakening the muscle surgically.
The muscle passes close under the macula, which is why bleeding at its insertion during surgery is avoided with care, and it wraps around the inferior rectus, which is why surgery on one affects the other.
Examine it
Overacts in a fourth nerve palsy, so the affected eye shoots up in adduction.
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