Medial rectus muscle

The medial rectus muscle is a muscle in the orbit near the eye. It is one of the extraocular muscles. It originates from the common tendinous ring, and inserts into the anteromedial surface of the eye. It is supplied by the inferior division of the oculomotor nerve (III). It rotates the eye medially (adduction).

Medial rectus
Rectus muscles:
2 = superior, 3 = inferior, 4 = medial, 5 = lateral
Oblique muscles: 6 = superior, 8 = inferior
Other muscle: 9 = levator palpebrae superioris
Other structures: 1 = Common tendinous ring, 7 = Trochlea, 10 = Superior tarsus, 11 = Sclera, 12 = Optic nerve
Figure showing the mode of innervation of the Recti medialis and lateralis of the eye.
Details
Origincommon tendinous ring at the orbital apex
Insertion5.5 mm medial to the limbus
Nerveinferior division of the oculomotor nerve
Actionsadducts the eyeball (makes it move inwards)
Identifiers
Latinmusculus rectus medialis bulbi
TA98A15.2.07.012
TA22044
FMA49037
Anatomical terms of muscle

Structure

The medial rectus muscle shares an origin with several other extrinsic eye muscles, the common tendinous ring. It inserts into the anteromedial surface of the eye.[1] This insertion has a width of around 11 mm.[1]

Nerve supply

The medial rectus muscle is supplied by the inferior division of the oculomotor nerve (III).[2] A branch of it enters the muscle around two fifths along its length.[2] It usually divides into 2 smaller branches, occasionally 3.[2] These further subdivide, becoming smaller down the length of the muscle until they become imperceptible to standard staining around 17 mm from the insertion of the muscle.[2]

Relations

The insertion of the medial rectus muscle is around 7.5 mm from the insertion of the superior rectus muscle, and around 6 mm from the inferior rectus muscle.[1] It is shorter but stronger than the other orbital recti muscles.[3] It rarely changes position significantly when it contracts, unlike the other extraocular muscles.[4]

Function

The medial rectus muscle rotates the eye medially (adduction).[5] It works using a pulley system as it curves around the anterior surface of the eye.[5]

Clinical significance

Strabismus

Strabismus (lazy eye) may be caused by a medial rectus muscle that is located too high in the orbit of the skull.[4]

Esotropia (convergent strabismus) may also be caused by sixth nerve palsy, which causes weakness or paralysis of the lateral rectus muscle.[6] Sometimes, botulinum toxin may be injected into the medial rectus muscle.[6] Whilst this reduces the ability to abduct and adduct the eye for tracking, it corrects the esotropia and so generally improves vision.[6]

Compression

The medial rectus muscle lies directly adjacent to the orbit of the skull.[7] This leaves it vulnerable to being compressed (incarcerated) during skull fractures, which can prevent movement of the eye.[7][8] This usually resolves when skull fractures are fixed.[7]

Surgical damage

The medial rectus muscle may be damaged during eye surgery or skull surgery, such as functional endoscopic sinus surgery.[9] The damage can be minor, such as bruising, or severe, such as cutting through the muscle partially or completely, and nerve injury.[9]

Additional images
  • Eye movement of medial rectus muscle, superior view.
  • Horizontal section of the eyeball.
  • Dissection showing origins of right ocular muscles, and nerves entering by the superior orbital fissure.
  • Vestibulo-ocular reflex
  • Medial rectus muscle
  • Medial rectus muscle
  • Extrinsic eye muscle. Nerves of orbita. Deep dissection.
  • Extrinsic eye muscle. Nerves of orbita. Deep dissection.
  • Extrinsic eye muscle. Nerves of orbita. Deep dissection.
  • Extrinsic eye muscle. Nerves of orbita. Deep dissection.
  • Extrinsic eye muscle. Nerves of orbita. Deep dissection.
  • Extrinsic eye muscle. Nerves of orbita. Deep dissection.

See also

References
  1. Apt, L (1980). "An anatomical reevaluation of rectus muscle insertions". Transactions of the American Ophthalmological Society. 78: 365–375. ISSN 0065-9533. PMC 1312149. PMID 7257065.
  2. Shin, Hyun Jin; Lee, Shin-Hyo; Ha, Tae-jun; Song, Wu-Chul; Koh, Ki-Seok (2019-05-04). "Intramuscular Nerve Distribution in the Medial Rectus Muscle and Its Clinical Implications". Current Eye Research. 44 (5): 522–526. doi:10.1080/02713683.2018.1562556. ISSN 0271-3683. PMID 30624996. S2CID 58560563.
  3. Standring, Susan (2016). Gray's anatomy: the anatomical basis of clinical practice (41 ed.). Elsevier Limited. pp. 666–685. ISBN 978-0-7020-5230-9.
  4. Clark, R. A.; Miller, J. M.; Demer, J. L. (1997-01-01). "Location and stability of rectus muscle pulleys. Muscle paths as a function of gaze". Investigative Ophthalmology & Visual Science. 38 (1): 227–240. ISSN 1552-5783. PMID 9008649.
  5. Porter, J. D.; Poukens, V.; Baker, R. S.; Demer, J. L. (1996-02-01). "Structure-function correlations in the human medial rectus extraocular muscle pulleys". Investigative Ophthalmology & Visual Science. 37 (2): 468–472. ISSN 1552-5783. PMID 8603853.
  6. Rosenbaum, Arthur L.; Kushner, Burton J.; Kirschen, David (1989-06-01). "Vertical Rectus Muscle Transposition and Botulinum Toxin (Oculinum) to Medial Rectus for Abducens Palsy". Archives of Ophthalmology. 107 (6): 820–823. doi:10.1001/archopht.1989.01070010842025. ISSN 0003-9950. PMID 2730398.
  7. McCulley, T.J.; Yip, C.C.; Kersten, R.C.; Kulwin, D.R. (2004-07-01). "Medial Rectus Muscle Incarceration in Pediatric Medial Orbital Wall Trapdoor Fractures". European Journal of Ophthalmology. 14 (4): 330–333. doi:10.1177/112067210401400409. ISSN 1120-6721. PMID 15309979. S2CID 196310817.
  8. Brannan, Paul A.; Kersten, Robert C.; Kulwin, Dwight R. (May 2006). "Isolated Medial Orbital Wall Fractures With Medial Rectus Muscle Incarceration". Ophthalmic Plastic & Reconstructive Surgery. 22 (3): 178–183. doi:10.1097/01.iop.0000217565.69261.4f. ISSN 0740-9303. PMID 16714925. S2CID 34406704.
  9. Huang, Christine M.; Meyer, Dale R.; Patrinely, James R.; Soparkar, Charles N. S.; Dailey, Roger A.; Maus, Marlon; Rubin, Peter A. D.; Yeatts, R. Patrick; Bersani, Thomas A.; Karesh, James W.; Harrison, Andrew R. (January 2003). "Medial Rectus Muscle Injuries Associated With Functional Endoscopic Sinus Surgery: Characterization and Management". Ophthalmic Plastic & Reconstructive Surgery. 19 (1): 25–37. doi:10.1097/00002341-200301000-00004. ISSN 0740-9303. PMID 12544790. S2CID 43492945.
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