Superior oblique muscle

The superior oblique muscle is one of the two oblique muscles of the eye. It lies in the superomedial part of the orbit and is primarily responsible for intorsion (inward rotation) of the eyeball, along with assisting in depression and abduction.

Origin and Insertion

• Origin: Body of the sphenoid bone, superomedial to the optic canal (above and medial to the common tendinous ring).

• Course: The muscle passes forward along the medial wall of the orbit, ending in a fibrous pulley called the trochlea, attached to the trochlear fovea of the frontal bone. Its tendon then turns posteriorly and laterally after looping through the trochlea.

• Insertion: Posterior, superior, and lateral surface of the sclera (outer posterior quadrant of the eyeball), behind the equator of the eyeball.

Note: Unlike the recti muscles, the oblique muscles insert posterior to the equator.

Nerve Supply

• Trochlear nerve (cranial nerve IV) — the only extraocular muscle supplied by this nerve.

Actions

• Primary action: Intorsion — rotates the top of the eyeball toward the nose.

• Secondary actions: Depression and abduction (moves the eye downward and outward).

Functional Note

When the eye is in the primary position, the superior oblique lies at an angle of about 51° to the visual axis. Because of this oblique alignment, its pull is directed downward, outward, and medially → causing depression, abduction, and intorsion.

In simple terms, the superior oblique pulls the eye down and out, while twisting the top of the eye toward the nose (intorsion).

Clinical Correlation

To test the superior oblique, the patient is asked to first adduct the eye (turn it medially), then look downward. This position aligns the visual axis with the muscle’s line of pull, isolating its depressing function.