Anatomy, Head and Neck, Eye Extraocular Muscles


Article Author:
Caleb Shumway
Mahsaw Motlagh


Article Editor:
Matthew Wade


Editors In Chief:
Jasleen Jhajj
Cliff Caudill
Evan Kaufman


Managing Editors:
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Frank Smeeks
Kristina Soman-Faulkner
Benjamin Eovaldi
Radia Jamil
Sobhan Daneshfar
Saad Nazir
William Gossman
Pritesh Sheth
Hassam Zulfiqar
Navid Mahabadi
Steve Bhimji
John Shell
Matthew Varacallo
Ahmad Malik
Mark Pellegrini
James Hughes
Beata Beatty
Hajira Basit
Phillip Hynes


Updated:
6/14/2019 5:49:32 PM

Introduction

There are 7 extraocular muscles. There are a total of 4 rectus muscles, 2 oblique muscles, and the levator palpebrae superioris. The 4 rectus muscles are the medial rectus, lateral rectus, superior rectus, and inferior rectus. The oblique muscles are the superior and inferior obliques. The levator palpebrae superioris is primarily responsible for eyelid elevation. [1]

Structure and Function

With head facing straight and the eyes facing straight ahead, the eyes are said to be in primary gaze. From this position, an action from an extraocular muscle produces a secondary or tertiary action. Although the globe can be moved about 50 degrees from primary position, usually during normal eye movement only 15 degrees of extraocular muscle movement occurs before the head movement begins. The rectus and oblique muscles are involved in the different gaze positions of the eye.

Each of the rectus and oblique muscles have a functional insertion point, which is at the closest point where the muscle first contacts the globe. This point forms a tangential line from the globe to the muscle origin and is known as the arc of contact.

The levator palpebrae superioris does not contact the globe directly but instead elevates the eyelid.[1]

Embryology

The mesenchyme of the head, including the orbit and its structures, arise primarily from 2 precursors, mesoderm, and neural crest cells. The extraocular muscles originate from mesoderm, but the satellite and connective tissue of the muscle arises from neural crest cells. Most of the remaining connective tissue of the orbit also is derived from neural crest cells.[2],[3]

Blood Supply and Lymphatics

The primary blood supply for all of the extraocular muscles are the muscular branches of the ophthalmic artery, the lacrimal artery, and the infraorbital artery. The ophthalmic artery has 2 muscular branches, which are the superior and inferior muscular branches. The lateral rectus receives blood from a branch of the lacrimal artery, and the other rectus muscles receive blood via 2 anterior ciliary arteries that communicate with a structure called the anterior circle of the ciliary body.

Venous drainage is similar to the arterial system and empties into the superior and inferior orbital veins. Usually, there are a total of 4 vortex veins, and these are found at the lateral and medial sides of the superior and inferior rectus muscles. These vortex veins drain into to the orbital venous system. [4]

Nerves

Cranial nerve III is divided into upper and lower divisions, with the upper division innervating the superior rectus as well as the levator palpebrae superioris, and the lower division to the medial rectus, the inferior rectus, and also to the inferior oblique. The superior oblique is innervated by cranial nerve IV (trochlear), and the lateral rectus is innervated by cranial nerve VI (abducens). [5]

Muscles

Each of the rectus muscles originates posteriorly at the Annulus of Zinn and courses anteriorly. These muscles insert on the globe at varying distances from the limbus, and the curved line drawn along the insertion points makes a spiral that is known as the Spiral of Tillaux. Starting at the medial aspect of the globe, the medial rectus inserts at 5.5 mm from the limbus, the inferior rectus inserts at 6.5 mm from the limbus, the lateral rectus inserts at 6.9 mm from the limbus, and the superior rectus at 7.7 mm from the limbus.

The superior oblique originates medial to the optic foramen and travels through the cochlea, a pulley at the superonasal portion of the orbital rim. From here the muscle travels under the superior rectus and inserts slightly posterior to the insertion of the superior rectus. The inferior oblique originates from a depression on the orbital floor near the orbital rim, travels posteriorly and inferiorly and inserts near the macula.

The levator palpebrae superioris originates from the lesser wing of the sphenoid and courses anteriorly. The body of the muscle travels over the superior rectus toward the eyelid. Where the connective tissue from the levator palpebrae superioris connects with similar tissue from the superior rectus, the Whitnall ligament is formed. Near this ligament, the levator palpebrae superioris fibers change to become more vertical, and they divide to the aponeurosis anteriorly and the superior tarsal muscle superiorly. [1]

Extraocular muscles have a large ratio of nerve fibers to skeletal muscle fibers. The ratio is 1:3 to 1:5, compared to other skeletal muscles which is 1:50 to 1:125. Extraocular muscles are a specialized form of skeletal muscle with a variety of fiber types, including both slow tonic types which resist fatigue and also saccadic (rapid) type muscle fibers. [6],[7]

Physiologic Variants

The size of the extraocular muscles, as well as its insertion point on the globe from the limbus and other anatomical measurements, may vary widely from one individual to the next. The numbers described in this article reflect average distances.

Occasionally, accessory extraocular muscles have been reported originating from the Annulus of Zinn and inserting in various locations. Both supernumerary and accessory extraocular muscles have been reported.

Congenital differences in extraocular muscles can cause ocular misalignment. See the Clinical Significance section for more details regarding strabismus. [1],[8]

Surgical Considerations

The nerves to rectus muscles and superior oblique muscles insert into the muscles at one-third the distance from the origin to the insertion. This makes damage to these nerves during anterior segment surgery difficult, but not impossible. Additionally, instruments that are advanced 26 mm posterior to the rectus muscle insertions can cause injury to the nerve.[9]

Blood vessels may be compromised during surgery of the inferior rectus muscle. The vessels which supply blood to the extraocular muscles also supply nearly all the temporal half of the anterior segment of the eye. Most of the nasal half of the anterior segment circulation is also derived from blood vessels that supply the extraocular muscles. Therefore, care must be taken during surgery of the medial rectus or other extraocular muscles to avoid disrupting this blood supply. [4],[10]

There are other complications which may result from strabismus surgery. Unsatisfactory alignment is the most common complication and may require additional surgery to correct this. Refractive changes may occur when two rectus muscles of one eye are operated, and this may resolve over months. Other possible surgical complications include diplopia, perforation of the sclera and postoperative infections. Although uncommon, serious infections may result after strabismus surgery, including pre-septal or orbital cellulitis and endophthalmitis.[11],[12],[13]

Clinical Significance

The function of the extraocular muscles can be assessed along with the other extraocular muscles during the clinical exam. The movement of the extraocular muscles can be assessed by having a patient look in nine directions. Starting with the primary gaze, followed by the secondary positions (up, down, left and right) and the tertiary positions (up and right, up and left, down and right, down and left). The clinician can test these positions by having the patient follow the clinician's finger trace a wide letter "H" in the air.

Further tests of ocular alignment can be tested further by several methods, including cover tests, corneal light reflex, dissimilar image tests and dissimilar target tests. Since many patients with extraocular muscle abnormalities are young children, the clinician may need to employ various clever means such as using toys or other objects to elicit the cooperation of the child.

Strabismus, or ocular misalignment, can be caused by abnormalities in binocular vision or abnormalities of neuromuscular control. Weakness, injury or paralysis that involves the inferior rectus muscle can be involved in strabismus.

Nerve palsies of the cranial nerves which innervate the extraocular muscles produce characteristic patterns which must be identified by the clinician. [14],[15]

Other Issues

There is a capsule of connective tissue known as the Tenon capsule which is an envelope that fuses with the optic sheath posteriorly and comes to meet the intermuscular septum anteriorly. The Tenon capsule helps the globe to stay positioned in orbit along with the extraocular muscles. [16]


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Attributed To: By OpenStax College [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

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Anatomy, Head and Neck, Eye Extraocular Muscles - Questions

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Which of these is not one of the extraocular muscles?



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Which of the following groups of cranial nerves (CN) innervate the seven extraocular muscles?



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What is the primary blood supply to the extraocular muscles?



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A 17-year-old female presents to the emergency department with intermittent double vision and sporadic weakness. The double vision is worsened by horizontal eye movements. There is no associated trauma or inciting event. She states that she has been under a lot of stress lately, but otherwise has no significant changes in terms of her social activity. MRI imaging reveals multiple enhancing lesions including the right midbrain and cerebral hemispheres. When the patient looks left, there is nystagmus noted in the left eye. Convergence testing is normal. Which of the following would be expected in the right eye when looking left?



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A 65-year-old male presents with the complaint of double vision following a bicycle accident two weeks ago. He notes that his symptoms are worsened with vertical eye movement. On exam, there is hypertropia of the right eye and is worsened with head tilt to the left. Which of the following extraocular movements is most likely impaired?



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A 17-year-old male presents to the emergency department with a severe headache and double vision. The patient has a history of IV drug use, and his roommate notes that his behavior has been erratic over the last two days. Past medical history is significant for HIV infection complicated by medication non-compliance. On initial assessment, the patient is noted to be febrile and appears in moderate distress. A lumbar puncture reveals elevated pressure, elevated protein, and low glucose. India ink staining confirms the diagnosis. Treatment is initiated, and the patient is admitted. Over the next few days, the patient continues to report double vision. On primary gaze, there is esotropia of the right eye. Which of the following muscles is most likely impaired?

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A 17-year-old male presents to the emergency department with a new-onset double vision following a closed head injury. The patient was skateboarding at a local park and sustained orbital trauma while attempting a new trick. On exam, there is mild hypertropia of the right eye on primary gaze and the patient has difficulty depressing his right eye during the assessment of extraocular movement. Which of the following provides vascular supply to the most likely injured muscle?



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A 65-year-old female presents following a new diagnosis of hyperthyroidism. On review of systems, the patient reports heat intolerance, and some anxiety despite starting medication last week. Hertel measurement confirms exophthalmos consistent with her diagnosis. In addition, on primary gaze, there is evidence of lid retraction. Which of the following extraocular muscles is most likely contributing to the lid retraction seen on the exam?

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Anatomy, Head and Neck, Eye Extraocular Muscles - References

References

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Surgical management of nonvascular lesions around the oculomotor nerve., Nonaka Y,Fukushima T,Friedman AH,Kolb LE,Bulsara KR,, World neurosurgery, 2014 May-Jun     [PubMed]
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Neural crest and the patterning of vertebrate craniofacial muscles., Ziermann JM,Diogo R,Noden DM,, Genesis (New York, N.Y. : 2000), 2018 Apr 16     [PubMed]
Pivotal role of orbital connective tissues in binocular alignment and strabismus: the Friedenwald lecture., Demer JL,, Investigative ophthalmology & visual science, 2004 Mar     [PubMed]
Risk of Anterior Segment Ischemia Following Simultaneous Three Rectus Muscle Surgery: Results from a Single Tertiary Care Centre., Tibrewal S,Kekunnaya R,, Strabismus, 2018 Mar 16     [PubMed]
Anterior segment ischemia: etiology, assessment, and management., Pineles SL,Chang MY,Oltra EL,Pihlblad MS,Davila-Gonzalez JP,Sauer TC,Velez FG,, Eye (London, England), 2018 Feb     [PubMed]
An anomalous muscle linking superior and inferior rectus muscles in the orbit., Kakizaki H,Zako M,Nakano T,Asamoto K,Miyaishi O,Iwaki M,, Anatomical science international, 2006 Sep     [PubMed]
A Case of Endophthalmitis After Bilateral Medial Rectus Recession., Patel SB,Reddy N,Hogan RN,Cao JH,, Journal of pediatric ophthalmology and strabismus, 2017 Jun 29     [PubMed]
Bilateral Orbital Abscesses After Strabismus Surgery., Dhrami-Gavazi E,Lee W,Garg A,Garibaldi DC,Leibert M,Kazim M,, Ophthalmic plastic and reconstructive surgery, 2015 Nov-Dec     [PubMed]
Subretinal abscess after strabismus surgery: case report and literature review., Patel CC,Goldenberg DT,Trese MT,Walsh MK,OʼMalley ER,, Retinal cases & brief reports, 2011 Winter     [PubMed]
An Eye on Vision: Five Questions About Vision Screening and Eye Health-Part 2., Nottingham Chaplin PK,Baldonado K,Cotter S,Moore B,Bradford GE,, NASN school nurse (Print), 2018 Jun 1     [PubMed]
Tzahor E, Head muscle development. Results and problems in cell differentiation. 2015     [PubMed]
Nottingham Chaplin PK,Baldonado K,Bradford GE,Cotter S,Moore B, An Eye on Vision: Five Questions About Vision Screening and Eye Health. NASN school nurse (Print). 2018 May     [PubMed]
Demer JL, Compartmentalization of extraocular muscle function. Eye (London, England). 2015 Feb     [PubMed]
Janbaz AH,Lindström M,Liu JX,Pedrosa Domellöf F, Intermediate filaments in the human extraocular muscles. Investigative ophthalmology & visual science. 2014 Jul 15     [PubMed]

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