Orbital part of orbicularis oculi

At a glance

English

Orbital part of orbicularis oculi

Latin (TA2)

Pars orbitalis musculi orbicularis oculi

System

Muscle

Region

Head

Side

Paired, left and right

About the orbital part of orbicularis oculi

The orbicularis oculi is the sphincter muscle around each eye and the only muscle that can close the eyelids. It is a broad, thin sheet that fills the lids, rings the margin of the orbit, and spreads outwards over the temple and down onto the cheek. Anatomists divide it into an orbital part, a palpebral part within the lids, and a small lacrimal part behind the tear sac. The orbital part is the outer and thickest of these, and its fibres are noticeably redder than the pale palpebral fibres.

It takes origin at the inner side of the orbit: from the frontal bone where it meets the nose, from the maxilla's frontal process just ahead of the tear-sac groove, and from the front face of the medial palpebral ligament. From there its fibres sweep around the orbital rim in an unbroken ellipse, passing outside the lateral corner of the eye without any interruption, and returning to the medial side. Its upper fibres mix with the frontalis and corrugator supercilii, and some of its lower fibres reach the skin of the cheek.

Unlike the palpebral part, which blinks automatically, the orbital part is under voluntary control and is used when the eyes are screwed shut. As it contracts, it pulls the skin of the brow, temple and cheek towards the inner corner of the eye, lowers the brow and lifts the cheek, giving forceful closure that protects the eye from a blow, dust or very bright light. The skin it gathers forms creases that fan out from the outer corner of the eye; with age these become the permanent lines called crow's feet. It can also act on its own while the lids stay open, narrowing the eye and lowering the brow to cut glare. Levator palpebrae superioris and the frontalis oppose it.

The muscle is supplied by the temporal and zygomatic branches of the facial nerve. A facial nerve lesion, as in Bell's palsy, leaves the eye unable to close on that side, so the cornea dries and may become inflamed or ulcerated; treatment ranges from lubricating drops to taping or surgical closure of the lids. The orbital part is also the usual target of botulinum toxin for crow's feet and for spasm of the eyelids.

Attachments, action and supply

Origin

Frontal bone beside the nose, the maxilla's frontal process ahead of the tear-sac groove, and the front face of the medial palpebral ligament.

Insertion

Runs as a complete ellipse around the orbital margin back to its origin; upper fibres blend with frontalis and corrugator, lower fibres reach the cheek skin.

Action

Closes the eyelids forcefully, as in screwing up the eyes; lowers the brow and draws the surrounding skin towards the inner corner of the eye.

Nerve supply

Temporal and zygomatic branches of the facial nerve (cranial nerve VII).

Blood supply

Branches of the facial, superficial temporal, supraorbital and infraorbital arteries, with the palpebral arteries.