Lateral rectus muscle

The lateral rectus is one of the four recti muscles of the eyeball. It lies along the lateral wall of the orbit and is the sole muscle responsible for abducting the eye — moving it away from the midline.

Origin and Insertion

• Origin: Common tendinous ring (annulus of Zinn) at the apex of the orbit.

• Insertion: Lateral surface of the sclera, anterior to the equator of the eyeball, approximately 7 mm posterior to the corneal limbus.

Note: Like the other recti muscles, the lateral rectus inserts into the anterior half of the globe, whereas the oblique muscles insert posterior to the equator.

Nerve Supply

• Abducent nerve (cranial nerve VI).

Actions

• Primary and only action: Abduction — moves the eyeball laterally (outward), away from the midline.

Functional Note

Unlike the superior and inferior rectus muscles, the lateral rectus muscle does not lie at an angle to the visual axis — instead, its line of pull is almost directly horizontal.

Because of this close alignment:

• When the muscle contracts, it pulls the eyeball directly outward, rotating it around the vertical axis of the globe.

• It does not elevate, depress, or rotate (torsion) the eye — its action is pure abduction.

Clinical Correlation

To test the lateral rectus, the examiner asks the patient to look laterally (outward). Failure to abduct the eye indicates possible abducent nerve (CN VI) palsy, often resulting in medial deviation (internal strabismus) of the affected eye in the primary position.