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Extraocular Muscles, Actions Last Updated: September 12, 2006 |
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| Synonyms and related keywords: monocular eye movements, ductions, binocular eye movements, conjugate, versions, disconjugate, vergences, horizontal rectus muscles, vertical rectus muscles, oblique muscles, saccadic eye movements, supranuclear control of the eye
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AUTHOR INFORMATION
| Section 1 of 7   |
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| Author: Robert H Graham, MD, Senior Associate Consultant, Department of Ophthalmology, Mayo Clinic, Scottsdale, Arizona Coauthor(s): D Brian Stidham, MD †, Former Clinical Assistant Professor, Department of Ophthalmology, Hermann Children's Hospital, University of Texas at Houston |
| Robert H Graham, MD, is a member of the following medical societies:
American Academy of Ophthalmology,
American Medical Association, and
Arizona Ophthalmology Society |
| Editor(s): James Goodwin, MD, Director of Neuro-Ophthalmology, Associate Professor, Departments of Neurology and Ophthalmology, University of Illinois College of Medicine; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine;
Robert Egan, MD, Neuro-Ophthalmology Fellowship Director, Associate Professor, Departments of Ophthalmology, Neurology, and Neurosurgery, Portland VAMC, Casey Eye Institute, Oregon Health & Science University;
Matthew J Baker, MD, Consulting Staff, Collier Neurologic Specialists, Naples Community Hospital;
and Nicholas Lorenzo, MD, Chief Editor, eMedicine Neurology; Consulting Staff, Neurology Specialists and Consultants |
Disclosure
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EYE MOVEMENTS
| Section 2 of 7   |
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Ductions are monocular eye movements.
- Movement of the eye nasally is adduction; temporal movement is abduction.
- Elevation and depression of the eye are termed sursumduction (supraduction) and deorsumduction (infraduction), respectively.
- Incycloduction (intorsion) is nasal rotation of the 12-o'clock position on the vertical meridian; excycloduction (extorsion) is temporal rotation of the 12-o'clock position on the vertical meridian.
- The primary muscle that moves an eye in a given direction is known as the agonist.
- A muscle in the same eye that moves the eye in the same direction as the agonist is known as a synergist, while a muscle in the same eye that moves the eye in the opposite direction of the agonist is an antagonist.
- For example, in abduction of the right eye, the right lateral rectus muscle is the agonist, the right superior and inferior oblique muscles are the synergists, and the right medial, superior, and inferior recti are the antagonists.
- By Sherrington law, increased innervation to any muscle (agonist) is accompanied by a corresponding decrease in innervation to its antagonists.
Binocular eye movements are either conjugate (versions) or disconjugate (vergences).
- Versions are movements of both eyes in the same direction (eg, right gaze in which both eyes move to the right).
- Dextroversion is movement of both eyes to the right, and levoversion is movement of both eyes to the left.
- Sursumversion (supraversion) and deorsumversion (infraversion) are elevation and depression of both eyes, respectively.
- Yoke muscles are the primary muscles in each eye that accomplish a given version; for right gaze, the right lateral rectus and left medial rectus muscles are the yoke muscles.
- Each extraocular muscle has a yoke muscle in the opposite eye to accomplish versions into each gaze position.
- By Herring law, yoke muscles receive equal and simultaneous innervation, the magnitude of which is determined by the fixing eye.
- Since the magnitude of innervation to yoke muscles is determined by the fixing eye, the angle of deviation between eyes (strabismus) may vary depending on which eye is fixing. The primary deviation is misalignment with the normal eye fixing. When the cause of deviation is acquired muscle paresis, as the paretic eye fixates, the ensuing secondary deviation is typically larger than the primary deviation. When the cause of deviation is congenital strabismus, the primary and secondary deviations are typically about the same.
- As opposed to versions (in which both eyes move in the same direction), vergences are movements of the eyes in opposite directions.
- Convergence is movement of both eyes nasally, and divergence is movement of both eyes temporally.
- Vertical vergence movements also may occur—one eye moving upward or the other downward relative to the contralateral eye.
- Accommodative convergence is convergence of the eyes stimulated by accommodation or focusing on a near target.
- Abnormality of the ratio of accommodative convergence to accommodation may cause certain types of strabismus.
- Fusional convergence and divergence are optomotor reflexes that are designed to position the eyes such that the image of regard falls on the fovea of each eye. This motor fusion is important to avoid diplopia (double vision).
- The field of action of an extraocular muscle is the direction of rotation of the eye when that muscle contracts. This term also indicates the gaze position in which the effects of a muscle are demonstrated most easily.
- Knowledge of fields of action is important; strabismus often increases in the field of action of a weak eye muscle.
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HORIZONTAL RECTUS MUSCLES
| Section 3 of 7 |
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The medial and lateral rectus muscles have only horizontal actions. The medial rectus muscle is the primary adductor of the eye, and the lateral rectus is the primary abductor.
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VERTICAL RECTUS MUSCLES
| Section 4 of 7 |
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- Superior and inferior rectus muscles are the primary vertical movers of the eye.
- The superior rectus acts as the primary elevator and the inferior rectus as the primary depressor of the eye. This vertical action is greatest with the eye in the abducted position.
- The direction of pull of the muscles forms a 23° angle relative to the visual axis in the primary position, giving rise to secondary and tertiary functions.
- The secondary action of the vertical rectus muscles is torsion.
- The superior rectus is an intorter, and the inferior rectus is an extorter.
- The tertiary action of both muscles is adduction.
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OBLIQUE MUSCLES
| Section 5 of 7 |
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- Superior and inferior oblique muscles are the primary muscles of torsion.
- The superior oblique creates intorsion, and the inferior oblique creates extorsion.
- As the direction of pull for both muscles forms a 51° angle (relative to the visual axis in the primary position), secondary and tertiary actions occur.
- The secondary action of the oblique muscles is vertical, which is best demonstrated when the eye is adducted with the superior oblique (depressor) and the inferior oblique (elevator).
- The tertiary action for each muscle is abduction.
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SUPRANUCLEAR CONTROL OF EYE MOVEMENTS
| Section 6 of 7 |
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The major conjugate eye movement systems are saccades and pursuit.
- The saccadic system controls rapid eye movement and acquires fixation (foveation) on the object of regard.
- The contralateral frontal eye fields in the frontal lobe control horizontal saccades. Some areas of the parietal lobe may assist in saccade generation.
- The right frontal lobe controls saccades to the left, and the left frontal lobe controls horizontal saccades to the right.
- The pursuit system controls smooth tracking for following slow-moving objects and maintains fixation (foveation) on the object of regard. Pursuit movements are controlled mostly by the ipsilateral parietal lobe (ie, right pursuit is driven by the right parietal lobe; left pursuit is driven by the left parietal lobe). In animal lesion studies, inputs to smooth pursuit are made by areas of the brain outside the parietal lobe.
- Most voluntary eye movements are a combination of saccade and pursuit eye movements, and the vestibulo-ocular reflex (doll's eye reflex) maintains foveation when the head is in motion.
- Control of the vergence system is presumed to lie at the level of the brain stem.
- Retinal disparity is believed to be the stimulus that drives divergence or convergence (motor fusion) to maintain sensory fusion and stereopsis.
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BIBLIOGRAPHY
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Ben Simon GJ, Syed HM, Douglas R, et al: Extraocular muscle enlargement with tendon involvement in thyroid-associated orbitopathy. Am J Ophthalmol 2004 Jun; 137(6): 1145-7[Medline].
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Catalano RA, Nelson LB: Anatomy of the Eye. Pediatric Ophthalmology. A Text Atlas
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Helveston EM: Surgical Anatomy. Surgical Management of Strabismus. 4th ed. St. Louis, Mo: Mosby-Year Book; 1993: 23-84.
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Jordan DR: Localization of extraocular muscles during secondary orbital implantation surgery: the tunnel technique: experience in 100 patients. Ophthalmology 2004 May; 111(5): 1048-54[Medline].
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Parks MM: Ocular Motility and Strabismus. Hagerstown, Md: Harper & Row; 1975.
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Von Noorden GN: Physiology of the Ocular Movements. Binocular Vision and Ocular Motility. 5th ed. St. Louis, Mo: Mosby-Year Book; 1996: 53-80.
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Wright K, ed: Anatomy and Physiology of the Extraocular Muscles. Pediatric Ophthalmology and Strabismus. St. Louis, Mo: Mosby-Year Book; 1995: 89-101.
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Yu Wai Man CY, Chinnery PF, Griffiths PG: Extraocular muscles have fundamentally distinct properties that make them selectively vulnerable to certain disorders. Neuromuscul Disord 2005 Jan; 15(1): 17-23[Medline].
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