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Orbital part of orbicularis oculi muscle

The orbital part of the orbicularis oculi is the outer circular portion of the eyelid muscle, surrounding the orbital rim. It plays a major role in forceful eyelid closure, blinking, and protection of the eye. Understanding its anatomy, function, and imaging appearance is essential for radiologists, ophthalmologists, and surgeons, particularly when evaluating trauma, eyelid tumors, or functional disorders.

Synonyms

  • Orbital portion of orbicularis oculi

  • Circular eyelid muscle (orbital segment)

  • Orbital eyelid sphincter muscle

Function

  • Enables forceful eyelid closure

  • Contributes to blinking and ocular protection

  • Facilitates lacrimal pump function, assisting tear drainage

  • Helps maintain eyelid tone and facial expression

MRI Appearance
T1-weighted images:

  • Appears as a thin, intermediate-signal intensity band encircling the orbital rim

  • Surrounded by hyperintense orbital fat, which provides natural contrast and clearly delineates muscle boundaries

  • Pathological changes such as inflammation, trauma, or tumors may appear hypointense or enhance with contrast

T2-weighted images:

  • Muscle remains intermediate signal, while edema or inflammation appears hyperintense, making abnormalities detectable

  • Orbital fat remains bright, improving visualization of the muscle margins

STIR (Short Tau Inversion Recovery):

  • Fat suppression enhances visualization of edema, inflammation, or infiltrative lesions

  • Normal muscle shows low-to-intermediate signal, while pathological changes appear bright hyperintense

CT Appearance

  • Muscle appears as a soft tissue density structure surrounding the orbital rim

  • Surrounded by hypodense orbital fat, providing clear anatomical contrast

  • Useful for detecting trauma, masses, or postoperative changes

MRI images

Orbital Part of Orbicularis Oculi Muscle axial image -img-00000-00000

MRI images

Orbital Part of Orbicularis Oculi Muscle axial sag image -img-00000-00000