The orbicularis oculi is a flat and broad circular-shaped muscle that covers the upper and lower eyelids and surrounds the opening of the eye, with fibers running in multiple directions. It also extends into the forehead, periorbital, temporal, and infraorbital regions, blending with the adjacent muscles.

Overall, the orbicularis oculi arises from the maxilla, frontal bone, lacrimal bone, lacrimal sac, and medial palpebral ligament. It inserts into the lateral palpebral raphe, the upper and lower tarsal plates, and the skin and soft tissue around the margin of the bony orbit.

The orbicularis oculi lies just beneath the skin and plays a crucial role in eyelid movement. The main function of this muscle is to close the eyelids, performing both involuntary and voluntary closures. It not only narrows the palpebral aperture but also protects the eyes from external irritants and contributes to tear drainage, maintaining proper eye lubrication and health. Additionally, it plays a vital role in facial expression, participating in actions such as squinting and frowning.

The orbicularis oculi consists of three parts, each with a specific function and distinct attachment sites:

Orbital part - the outermost portion that encircles the orbit; enables forceful eyelid closure, such as when squinting;
Palpebral part - the thinner portion located within the eyelids; it allows gentle blinking and soft closure;
Lacrimal part (deep palpebral part) - a small, deep portion that assists in tear drainage by compressing the lacrimal sac.

The orbicularis oculi receives its arterial blood supply from branches of the internal carotid artery and external carotid artery. All parts are innervated by the temporal and zygomatic branches of the facial nerve (CN VII).

Note: Interestingly, about 88% of the fibers in the orbicularis oculi are fast-twitch fibers, while around 12% are slow-twitch fibers.

Orbital part

The orbital part is the outermost portion of the orbicularis oculi. It surrounds the bony orbit and is responsible for the voluntary, forceful closure of the eyelids during actions such as squinting, reacting to bright light, or protective eye closure. Unlike the palpebral part, which handles gentle eyelid closure, the orbital part is activated when strong muscle contraction is needed. It serves not only a protective function but also plays an important role in facial expressions associated with distress, pain, or intense focus.

The orbital part of the orbicularis oculi encircles the bony orbit completely, also extending into the neighboring soft tissues and blending with adjacent muscles along its periphery. The upper fibers of the orbital part merge with the fibers of the frontalis, corrugator supercilii, and depressor supercilii muscles. This blending makes the orbital part integral to facial expressions involving the forehead and eyebrows.

Origin: nasal part of the frontal bone, frontal process of the maxilla, and the medial palpebral ligament.

Insertion: lateral palpebral raphe (a fibrous band at the lateral corner of the eye). Fibers of the orbital part of the orbicularis oculi also blend with neighboring soft tissues and muscles along its periphery.

Action: forcefully and tightly closes the eyelids and narrows the space between them. It also helps draw the skin of the forehead, temple, and cheek toward the eye, contributing to facial expressions like squinting or frowning. This part helps limit exposure to potentially harmful factors such as blowing dusts or bright sunlight.

Innervation: temporal and zygomatic branches of the facial nerve (CN VII).

Arterial blood supply: angular artery of the facial artery; transverse facial artery of the superficial temporal artery; supraorbital, supratrochlear, and medial palpebral arteries of the ophthalmic artery; lateral palpebral arteries of the lacrimal artery. It may also receive contributions from the infraorbital artery of the maxillary artery.

Venous drainage: tributaries of the superior and inferior ophthalmic veins, facial vein, and superficial temporal vein.

Palpebral part

The palpebral part is a thin portion of the orbicularis oculi that lies within the upper and lower eyelids. It is responsible for the gentle closure of the eyelids - during blinking or when closing the eyes during sleep. It functions involuntarily in the blink reflex to keep the eyeball moist and protected, and voluntarily during soft eye closure.

Origin: superficial surface of the medial palpebral ligament and the adjacent part of the frontal process of the maxilla.

Insertion: lateral palpebral raphe (a fibrous band at the lateral corner of the eye).

Action: pulls the upper eyelid down and raises the lower eyelid, gently closing the eyelids when blinking. The palpebral part also closes the eyelids involuntarily as a reflex mechanism. Additionally, it plays a crucial role in spreading tears across the surface of the eyeball to keep it moist and free of potentially irritating particles. All these actions also facilitate non-verbal communication and expression.

Innervation: temporal and zygomatic branches of the facial nerve (CN VII).

Arterial blood supply: angular artery of the facial artery, transverse facial artery of the superficial temporal artery, medial palpebral arteries of the ophthalmic artery, and lateral palpebral arteries of the lacrimal artery.

Venous drainage: tributaries of the superior and inferior ophthalmic veins and the facial vein.

Lacrimal or deep palpebral part

The lacrimal part of the orbicularis oculi is a small, deep portion of the muscle located in the medial corner of the eye. It is also known as the deep palpebral part and is sometimes referred to as the Horner's muscle. This part works in coordination with the rest of the orbicularis oculi to support tear drainage.

The main function of the lacrimal part is to assist in the drainage of tears by pulling the eyelid medially and compressing the lacrimal sac during blinking. This action helps pump tears through the lacrimal apparatus toward the nasolacrimal duct. Although a small part, it plays an essential role in maintaining healthy eye lubrication and tear flow.

Origin: posterior lacrimal crest of the lacrimal bone and adjacent portion of the lacrimal sac.

Insertion: superior and inferior tarsal plates of the eyelids; lateral palpebral raphe. It blends with the fibers of the palpebral part of the orbicularis oculi.

Action: draws the eyelids medially and compresses the lacrimal sac, facilitating tear drainage through the nasolacrimal duct.

Innervation: zygomatic branch of the facial nerve (CN VII).

Arterial blood supply: angular artery of the facial artery and dorsal nasal artery of the ophthalmic artery. It may also receive contributions from the infraorbital artery of the maxillary artery.

Venous drainage: angular vein that drains into the facial vein; superior and inferior ophthalmic veins that drain into the cavernous sinus.

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Orbicularis oculi