Lateral rectus muscle

At a glance

English

Lateral rectus muscle

Latin (TA2)

Musculus rectus lateralis bulbi oculi

System

Muscle

Region

Head

Side

Paired, left and right

About the lateral rectus muscle

The lateral rectus is one of the extraocular muscles and the one responsible for abduction, swinging the front of the eye outwards towards the temple. It lies against the lateral wall of the orbit, between the eyeball and the bone, and it is the one eye muscle the abducens nerve serves. Its partner across the eye is the medial rectus, and the two together control horizontal gaze.

It arises from the outer segment of the common tendinous ring, the fibrous ring at the orbital apex that encircles the optic canal and part of the superior orbital fissure. Some fibres also come from a small spine on the greater wing of the sphenoid. The ring is shared by all four recti, while the superior oblique arises just above it and the inferior oblique far forward on the floor. The lateral rectus runs forwards along the outer wall and inserts by a tendon roughly a centimetre wide on the temporal side of the sclera, about 7 mm behind the edge of the cornea. Since the ring bridges the fissure, several nerves, among them the oculomotor, nasociliary and abducens, pass into the orbit inside the cone the recti form.

Its action is simple: it abducts the eye, rotating it outwards about a vertical axis without significant elevation or rotation. The abducens nerve that drives it arises from a nucleus in the pons, leaves the brainstem at the junction of pons and medulla, climbs a long course over the petrous apex, passes through the cavernous sinus and passes the superior orbital fissure to reach the inner surface of the muscle. To test it, the patient follows a target out to the side.

Because of that long path, the abducens nerve is easily affected by stroke, injury, tumours, inflammation or infection, and especially by any rise in pressure inside the skull. In a sixth nerve palsy the eye cannot turn outwards, it drifts towards the nose under the unopposed medial rectus, and the patient sees two images side by side, worse when looking towards the weak side. Recovery depends on the cause: palsies after a viral illness often improve, while those due to trauma or a tumour may not. Duane syndrome, a congenital failure of the abducens nerve to develop normally, also limits abduction.

Attachments, action and supply

Origin

Outer segment of the common tendinous ring at the apex of the orbit.

Insertion

Temporal side of the sclera, about 7 mm behind the corneal limbus.

Action

Abducts the eye, turning the cornea away from the midline.

Nerve supply

Abducens nerve (cranial nerve VI).

Blood supply

Lateral muscular branch of the ophthalmic artery, with a contribution from the lacrimal artery.