Lateral rectus muscle
The lateral rectus muscle is one of the 4 straight muscles of the orbit responsible for the movement of the eye in the cardinal directions. These muscles, along with the superior and inferior oblique muscles, belong to the extraocular muscles of the eye.
The lateral rectus muscle arises from the common tendinous ring and runs anteriorly and across the lateral part of the orbit to insert at the lateral side of the eyeball. Like other straight muscles, the lateral rectus is named by its position within the orbit relative to the eyeball.
The primary action of the lateral rectus muscle is abduction of the eyeball. It works in synergy or opposition with other extrinsic muscles of the eye to produce coordinated movements and direct the gaze.
|Common tendinous ring (Annulus of Zinn)
|Anterior half of eyeball (posterior to corneoscleral junction)
|Abducens nerve (CN VI)
This article will discuss the anatomy and functions of the lateral rectus muscle of the eye.
Origin and insertion
The lateral rectus muscle is a flat strap-shaped muscle that is wider in its anterior part. It arises from the lateral part of the common tendinous ring and crosses the superior orbital fissure. Additionally, a small slip arises from a spine on the greater wing of the sphenoid bone. The muscle then runs anteriorly along the lateral wall of the orbit to insert at the lateral side of the eyeball after crossing the tendon of the inferior oblique muscle. The muscle inserts anterior to the equator of the eyeball, about 7 mm from the limbus of the cornea.
The lateral rectus muscle extends along the lateral wall of the orbit. It arises from the lateral part of the common tendinous ring near the attachments of the medial, lateral and superior recti muscles. This tendinous ring encircles the margins of the optic canal and part of the superior orbital fissure, hence the attached muscles form a cone which envelops the structures entering the orbit. These structures include the optic sheath containing the optic nerve (CN II) and ophthalmic artery, the superior and inferior divisions of oculomotor nerve (CN III), the nasociliary nerve (CN V₁) and abducens nerve (CN VI).
After arising from the common tendinous ring, the lateral rectus lies lateral to the ciliary ganglion near the apex of the orbit. The lateral rectus muscle then runs along the lateral wall of the orbit towards the eyeball, passing medially to the lacrimal gland. In addition, the lacrimal artery runs along the superior border of the lateral rectus muscle to supply the lacrimal gland.
The fascial sheath of the lateral rectus muscle gives off a triangular expansion called the lateral check ligament. This ligament attaches to the orbital tubercle of the zygomatic bone and serves to restrict the lateral rectus muscle and limit the abduction of the eye. The lateral check ligament blends with the same fascial expansions of the medial and inferior rectus muscle, as well as superior and inferior oblique muscles. Together, they form the suspensory ligament of the eyeball, a hammock-like sling that provides support to the eyeball.
The lateral rectus muscle is supplied by branches of the abducens nerve (CN VI), which enter its medial surface and provide general somatic efferent fibers.
The lateral rectus muscle is supplied by the ophthalmic artery that stems from the internal carotid artery. The ophthalmic artery supplies it either directly, or through its lacrimal branch.
The lateral rectus muscle abducts the eye and directs the gaze laterally in the horizontal plane. This action is assisted by the superior and inferior oblique muscles which also abduct the eyes among their other functions.
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To abduct the gaze, the lateral rectus in one eye muscle has to work in coordination with the medial rectus of the other eye, in which the medial rectus needs to relax when the lateral rectus contracts. These muscles are referred to as yoke muscles; described as functionally-paired contralateral synergists that produce conjugate ocular movements.Visit the following page and learn all the muscles that move the eyes!
Damage to the abducens nerve (CN VI) can result in paralysis of the lateral rectus muscle. This condition is called abducens nerve palsy. This condition can occur from an expanding lesion such as a tumour or a cyst that compresses the abducens nerve itself or its nucleus. The main symptoms of abducens nerve palsy are reflected in the lateral rectus dysfunction, in which the eye is unable to move laterally. Since the abducens nerve only innervates the lateral rectus, other extraocular muscles will not be affected. Therefore, the muscle that is functionally antagonistic to the lateral rectus will overpower it and pull the eyeball on their side. This results in the eyes being fully adducted by the unopposed medial rectus muscle.
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