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The orbicularis oculi muscle is responsible for eyelid movement and is situated just beneath the skin of both the upper and lower eyelids. It extends from the medial to the lateral canthal region, enhancing the eyelid's structural integrity and functionality. The main function of the orbicularis oculi muscle is to close the eyelids, and it also assists with tear drainage. The levator palpebrae superioris, on the other hand, is the only muscle involved in raising the upper eyelid. It is innervated by the oculomotor nerve and is responsible for elevating and retracting the superior eyelid.
| Characteristics | Values |
|---|---|
| Muscle Name | Orbicularis Oculi |
| Location | Beneath the eyelid skin |
| Function | Eyelid movement, closing the eyelids, assisting with tear drainage |
| Structure | Three distinct parts – palpebral, lacrimal and orbital |
| Attachments | Originates from the medial orbital margin, the medial palpebral ligament, and the lacrimal bone |
| Innervation | Facial nerve (orbicularis oculi), oculomotor nerve (levator palpebrae superioris) and sympathetic fibres (superior tarsal muscle) |
| Conditions | Bell Palsy, blepharospasm, Horner's syndrome, oculosympathetic palsy |
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What You'll Learn
The orbicularis oculi muscle
The palpebral portion of the muscle is thin and pale, and it arises from the bifurcation of the medial palpebral ligament. It is further divided into preseptal, pretarsal, and ciliary sections. The preseptal section is split into deep and superficial heads, with the former attaching to the fascia around the lacrimal sac and the posterior lacrimal crest, and the latter attaching to the anterior limb of the medial canthal ligament. The pretarsal section is also divided into deep and superficial heads, with the deep head, or Horner muscle, attaching to the medial canthal tendon and the posterior lacrimal crest. The ciliary (marginal) section of the palpebral orbicularis muscle, also known as the muscle of Riolan, is adjacent to the eyelid margin.
The lacrimal part of the orbicularis oculi muscle is a small, thin muscle situated behind the medial palpebral ligament and lacrimal sac. It arises from the posterior crest and adjacent part of the orbital surface of the lacrimal bone and divides into two slips, upper and lower, which are inserted into the superior and inferior tarsi. The lacrimal orbicularis facilitates the tear pump into the lacrimal sac.
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The levator palpebrae superioris muscle
The levator palpebrae superioris is attached to the check ligament of the superior rectus muscle, and they contract simultaneously. The levator palpebrae superioris is separated from the eyeball by the superior rectus muscle, and both muscles are enclosed by connective tissue sheaths. The levator palpebrae superioris is a skeletal muscle, not a smooth muscle.
The muscle fibres of the levator palpebrae superioris penetrate the upper eyelid, inserting into its parts via two aponeurotic fascicles. Deep fibres attach to the anterior surface of the superior tarsus, while superficial fibres radiate through the eyelid and orbicularis oculi to attach to the skin of the superior eyelid. The most lateral fibres of the muscle's aponeurosis attach to the orbital tubercle of the zygomatic bone, while the most medial fibres attach to the medial palpebral ligament.
The levator palpebrae superioris receives a rich blood supply, mainly from the ophthalmic and supraorbital arteries, which are branches of the internal carotid artery. The muscle is innervated by the superior branch of the oculomotor nerve (CN III), which originates in the midbrain and exits the cranium through the superior orbital fissure.
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The tarsal plates
The medial angles of the two plates end at the lacrimal lake and are attached to the frontal process of the maxilla by the medial palpebral ligament. The medial palpebral ligament, also known as the medial canthal tendon (MCT), is a band of fibrous tissue that holds the inner aspect of the tarsal plates in place. The MCT is composed of an anterior limb formed by a small part of the superficial aspect of the orbicularis muscle that lies behind the tarsus. The deeper part of the orbicularis muscle inserts into the back of the lacrimal crest and the lacrimal sac fascia.
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The superior tarsal muscle
The main function of the superior tarsal muscle is to elevate the upper eyelid, particularly in states of sympathetic predominance such as excitement, fear, or surprise. This action enables a wider visual field in acute life-threatening situations, triggering a fight-or-flight response. The static tone of the muscle also helps to maintain the eyes open and keep the size of the palpebral fissure constant during wakefulness.
Damage to certain elements of the sympathetic nervous system can inhibit the superior tarsal muscle, resulting in a drooping eyelid, a condition known as partial ptosis.
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The oculomotor nerve
One of the key functions of the oculomotor nerve is its involvement in eyelid movement. It innervates the levator palpebrae superioris muscle, which is responsible for raising the upper eyelid. Additionally, sympathetic fibres travel along with the superior branch of the oculomotor nerve to innervate the superior tarsal muscle, which helps maintain the eyelid in an elevated position.
Furthermore, the oculomotor nerve helps adjust and coordinate eye position during different types of eye movements, such as saccades (rapid, jerky motions between objects), smooth pursuit (tracking an object), and fixation (staring at an object). It also receives sympathetic branches from the internal carotid plexus, which contribute to its overall function.
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Frequently asked questions
The orbicularis oculi muscle is responsible for lowering the upper eyelid.
The orbicularis oculi muscle is situated just beneath the skin of the eyelid and is critical in eyelid movement. It extends from the medial to the lateral canthal region, supporting the eyelid's structural integrity and functionality.
The levator palpebrae superioris and superior tarsal muscles are involved in raising the upper eyelid. The superior tarsal muscle is innervated by the sympathetic nervous system.
The main function of the orbicularis oculi muscle is to close the eyelids, and it also assists with tear drainage.
