Levator palpebrae superioris

At a glance

English

Levator palpebrae superioris

Latin (TA2)

Levator palpebrae superioris

System

Muscle

Region

Head

Side

Paired, left and right

About the levator palpebrae superioris

The levator palpebrae superioris, the elevator of the upper eyelid, lies in the roof of the orbit, just above the superior rectus and below the orbital plate of the frontal bone. Although it sits among the eye muscles, it does not move the eyeball; it acts only on the upper lid. It is a skeletal muscle under voluntary control, but it is also tonically active the whole time we are awake, holding the lid up against gravity.

It begins as a narrow tendon on the under surface of the sphenoid's lesser wing, just above and in front of the optic canal. It runs forward over the superior rectus, gradually becoming wider and thinner, and near the front of the orbit it changes into a broad fibrous sheet, the levator aponeurosis. This sheet fans out across the width of the lid. Some of its fibres pass forwards through orbicularis oculi to the skin, forming the upper lid crease, others attach to the front of the superior tarsus, and its outer and inner edges, the horns, anchor to the orbital walls near the palpebral ligaments. A thin layer of smooth muscle, the superior tarsal muscle, arises from the underside of the levator and inserts on the upper border of the tarsus.

Contraction lifts the upper lid, uncovering the cornea, and its tone keeps the eye open; relaxation allows orbicularis oculi to close the lid. The striated part is supplied by the upper division of the oculomotor nerve, which reaches it after supplying the superior rectus, while the superior tarsal muscle is driven by sympathetic fibres from the superior cervical ganglion. Blood comes from muscular branches of the ophthalmic artery and from the supraorbital artery, and drains to the superior ophthalmic vein.

Failure of this mechanism causes ptosis, a drooping eyelid. A palsy of the oculomotor nerve paralyses the levator itself, so the lid falls heavily and may cover the eye completely. Loss of the sympathetic supply, as in Horner syndrome, affects only the superior tarsal muscle and gives a slight droop of a millimetre or two, together with a small pupil. The two are usually told apart by these accompanying signs. In older people the aponeurosis can stretch or detach from the tarsus, the commonest cause of ptosis.

Attachments, action and supply

Origin

Under surface of the sphenoid's lesser wing, above and in front of the optic canal.

Insertion

Through the levator aponeurosis into the upper eyelid skin and the front of the superior tarsus; the superior tarsal muscle reaches the tarsal border.

Action

Raises the upper eyelid and holds it open.

Nerve supply

Upper division of the oculomotor nerve (cranial nerve III); sympathetic fibres from the superior cervical ganglion to its smooth-muscle part.

Blood supply

Muscular branches of the ophthalmic artery and the supraorbital artery; drained by the superior ophthalmic vein.