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Medial rectus muscle

The medial rectus muscle is one of the six extraocular muscles responsible for controlling eye movements. Situated on the medial (nasal) side of the orbit, it plays a crucial role in adducting the eye, allowing it to move towards the nose. The muscle originates from the common tendinous ring at the orbital apex and inserts onto the anteromedial aspect of the sclera, just posterior to the corneoscleral junction. Due to its key role in ocular motility, the medial rectus is frequently evaluated in neuro-ophthalmological and radiological assessments.

Synonyms

  • Medial rectus oculi muscle

  • MR muscle

  • Medial rectus

  • Internal rectus muscle

Function

  • Primary Action: Adduction of the eyeball (moves the eye medially, towards the nose)

  • Secondary Actions: None (pure adductor)

  • Nerve Supply: Oculomotor nerve (cranial nerve III), inferior division

  • Clinical Role: Essential in coordinated binocular vision and convergence

MRI Appearance

  • T1-weighted images:

    • Appears as a well-defined, ovoid structure along the medial orbital wall

    • Isointense to other extraocular muscles and similar to skeletal muscle signal

  • T2-weighted images:

    • Slightly hyperintense compared to T1

    • Maintains a homogeneous, intermediate signal

  • STIR sequence:

    • Normal muscle appears β€‹slightly hyperintense (mildly bright) compared to T2 and T1 due to fat suppression.

CT Appearance

  • Appears as a soft-tissue density muscle, oval in cross-section

  • Lies adjacent to the medial orbital wall (lamina papyracea)

  • Well-demarcated margins in axial and coronal sections

MRI images

Medial rectus muscle mri image