Superior rectus muscle

The superior rectus is one of the extraocular muscles responsible for movements of the eyeball. It lies in the superior aspect of the orbit and forms part of the group of four recti muscles.

Origin and Insertion

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

• Insertion: Superior aspect of the sclera, anterior to the equator of the eyeball (i.e. in the anterior half of the globe), a few millimetres posterior to the corneal limbus.

  Note: All recti muscles attach to the anterior half of the eyeball, whereas the oblique muscles insert posterior to the equator.

Nerve Supply

• Oculomotor nerve (cranial nerve III) — specifically, its superior division.

Actions

The actions of the superior rectus depend on the position of the eyeball:

• Primary action: Elevation of the eyeball.

• Secondary actions: Adduction (movement towards the midline) and medial rotation (intorsion).

Functional Note

The superior rectus attaches to the upper surface of the eyeball, in front of its horizontal equator. When it contracts, it pulls the superior pole of the eyeball upward, causing elevation.

Each orbit is oriented approximately 23° laterally (outward) from the midline of the head, whereas the visual axis (the line of gaze) is directed straight ahead. Therefore, when the eye is in the primary (straight-ahead) position, the superior rectus is not aligned with the visual axis — it runs 23° outward relative to it.

Because its pull is oblique rather than vertical, contraction of the muscle not only elevates the eye but also pulls the eyeball a little inwards towards the nose, i.e.:

• It pulls it slightly medially, producing adduction (along a vertical axis), and

• It rotates the superior pole medially, producing intorsion (along an antero-posterior axis).

In simple terms, the superior rectus pull the eye up and slightly in, so it elevates, adducts, and intorts the eyeball simultaneously. However, when the eye is abducted by the lateral rectus (turned outward by ~23°), the line of pull of the superior rectus becomes almost vertical, allowing it to act purely as an elevator.

Clinical Correlation

To isolate and test the functions of the superior and inferior rectus muscles, the examiner asks the patient to first move the eyes laterally, following the examiner’s finger. This lateral movement aligns the visual axis of the eyeball with the long axis of the superior and inferior rectus muscles. The patient is then instructed to look upward to test the superior rectus, or downward to test the inferior rectus.