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Orbicularis oculi muscle (Orbital part)

The orbicularis oculi muscle is a key muscle of facial expression that surrounds the orbit and plays a vital role in eyelid closure. The orbital part of the muscle forms the outermost circular fibers and is responsible for forceful voluntary closure of the eyelids, such as during squinting. It is distinct from the palpebral and lacrimal parts of the orbicularis oculi and is essential for protecting the eye from injury and light. Understanding its detailed anatomy, function, nerve and blood supply, and imaging characteristics is crucial for clinical assessment, surgery, and radiology.

Synonyms

  • Orbital part of orbicularis oculi

  • Pars orbitalis musculi orbicularis oculi (Latin)

  • Orbital portion of orbicularis oculi

Function

  • Responsible for forceful closure of the eyelids (e.g., tight squeezing or squinting)

  • Protects the eye from foreign bodies, bright light, and injury

  • Assists in expression of emotions such as anger or determination

Origin

  • Medial orbital margin: Primarily from the frontal process of the maxilla and nasal part of the frontal bone

  • Medial palpebral ligament: Contributes some fibers

Insertion

  • Circumferential fibers: Encircle the orbit and insert into the skin and subcutaneous tissue around the orbit, including the lateral palpebral raphe

Nerve Supply

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

Arterial Supply

  • Ophthalmic artery (main branch: zygomatico-orbital artery)

  • Facial artery (angular branch)

  • Superficial temporal artery (lateral orbital branch)

  • Infraorbital artery (minor supply)

Venous Drainage

  • Ophthalmic veins (superior and inferior)

  • Facial vein

  • Superficial temporal vein

MRI Appearance

  • T1-weighted images: The orbital part of orbicularis oculi appears as an intermediate signal intensity muscle surrounding the orbit, well delineated from adjacent orbital fat (which is hyperintense).

  • T2-weighted images: Normal muscle demonstrates relatively low signal intensity, but increased signal may indicate edema or pathology.

  • STIR (Short Tau Inversion Recovery): Muscle shows low signal intensity in healthy tissue; hyperintensity is seen if there is edema, inflammation, or acute injury.

CT Appearance

  • CT imaging: The orbital part appears as a thin, soft tissue density band encircling the orbital rim, isodense to other facial muscles, well separated from orbital fat and bone.

MRI images

Orbicularis oculi muscle (Orbital part) mri axial image 1 -img-00000-00000

MRI images

Orbicularis oculi muscle (Orbital part) mri axial image -img-00000-00000