Orbicularis oculi muscle

The orbicularis oculi is a broad, thin, circular muscle of facial expression surrounding the orbit and eyelids. It functions primarily to close the eyelids, protect the eyeball, and facilitate lacrimal drainage by distributing tears across the corneal surface. The muscle consists of three distinct parts — orbital, palpebral, and lacrimal — each contributing differently to eyelid movement and tear flow.

Anatomical Description

1. Origin

• Nasal part of the frontal bone

• Frontal process of the maxilla (anterior to the lacrimal groove)

• Anterior surface and borders of the medial palpebral ligament

2. Course

From these origins, the fibres pass laterally to form a broad, thin muscular sheet that occupies the eyelids, surrounds the orbit, and extends over the temple and upper cheek.

Parts and Structure

1. Palpebral Part

• Location: Within the upper and lower eyelids

• Origin: From the medial palpebral ligament

• Course & Insertion: Fibres form concentric curves and meet laterally at the lateral palpebral ligament/raphe

• Function: Produces gentle eyelid closure, as in blinking or sleeping

2. Orbital Part

• Location: Surrounds the orbital rim

• Appearance: Thicker than the palpebral part

• Fibres: Form a complete uninterrupted ellipse around the orbit

• Relations: Superior fibers blend with the frontalis and corrugator supercilii muscles

• Function: Responsible for forceful closure of the eyelids, as in squinting or protection from bright light

3. Lacrimal Part (Tensor Tarsi or Horner’s Muscle)

• Location: Posterior to the medial palpebral ligament and lacrimal sac

• Origin: Posterior lacrimal crest and adjacent orbital surface of the lacrimal bone

• Course: Passes behind the lacrimal sac and divides into superior and inferior slips

• Insertion: Into the medial ends of the superior and inferior tarsi

• Function: Assists in tear drainage by compressing the lacrimal sac

Innervation

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

Blood Supply

Branches of the facial, superficial temporal, and ophthalmic arteries (including the supraorbital and infraorbital arteries).

Clinical Relevance

Facial nerve palsy (Bell’s palsy): Causes inability to close eyelids and risk of corneal drying or ulceration.