Jump to content

Ciliary muscle: Difference between revisions

From Wikipedia, the free encyclopedia
Browse history interactively
← Previous edit
Content deleted Content added
VisualWikitext
Tarquilu (talk | contribs)
280 edits
Citation bot (talk | contribs)
Bots
5,353,173 edits
Added pmid. | Use this bot. Report bugs. | Suggested by Chris Capoccia | #UCB_toolbar
 
(199 intermediate revisions by more than 100 users not shown)
Line 1: Line 1:
{{short description|Eye muscle which is used for focussing}}
{{Infobox Muscle |
Name = Ciliary muscle |
{{Infobox muscle
| Name = Ciliary muscle
Latin = musculus ciliaris |
| Latin = musculus ciliaris
| Image = Gray872.png
GraySubject = 225 |
| Caption = The [[choroid]] and [[Iris (anatomy)|iris]]. (Ciliary muscle is labeled near top.)
GrayPage = 1011 |
Image = Gray872.png |
| Image2 =
| Caption2 =
Caption = The [[choroid]] and [[Iris (anatomy)|iris]]. (Ciliary muscle is labeled near top.) |
| Origin = 1) longitudinal fibers → [[scleral spur]]; 2) circular fibers → encircle root of iris<ref name="Gest">Gest, Thomas R; Burkel, William E. "Anatomy Tables - Eye." Medical Gross Anatomy. 2000. University of Michigan Medical School. January 5, 2010 [http://anatomy.med.umich.edu/nervous_system/eye_tables.html Umich.edu] {{webarchive|url=https://web.archive.org/web/20100526064035/http://anatomy.med.umich.edu/nervous_system/eye_tables.html |date=2010-05-26 }}</ref>
Image2 = |
| Insertion = 1) longitudinal fibers → ciliary process, 2) circular fibers → encircle root of iris<ref name=Gest/>
Caption2 = |
| Blood = [[Long posterior ciliary arteries]]
Precursor = |
System = |
| Vein = [[Vorticose veins]]
| Nerve = [[Short ciliary nerves|Short ciliary]]<br>Parasympathetic fibers in the [[oculomotor nerve|oculomotor nerve (CN-III)]] synapse in the [[ciliary ganglion]]. Parasympathetic postganglionic fibers from the [[ciliary ganglion]] travel through [[short ciliary nerves]] into the ocular globe.
Origin = 1) longitudinal fibers → [[scleral spur]]; 2) circular fibers →: encircle root of iris<ref name="Gest">Gest, Thomas R; Burkel, William E. "Anatomy Tables - Eye." Medical Gross Anatomy. 2000. University of Michigan Medical School. 5 Jan. 2010 <http://anatomy.med.umich.edu/nervous_system/eye_tables.html>.</ref> |
| Action = 1) [[Accommodation reflex|Accommodation]], 2) regulation of [[trabecular meshwork]] pore sizes
Insertion = 1) longitudinal fibers → ciliary process, 2) circular fibers → encircle root of iris<ref name=Gest/> |
| Pronunciation = {{IPAc-en|UK|ˈ|s|ɪ|l|i|ə|r|i}}, {{IPAc-en|US|ˈ|s|ɪ|l|i|ɛr|i}}<ref>{{cite LPD|3}}</ref>
Blood = [[long posterior ciliary arteries]] |
Vein = [[Vorticose vein]] |
Nerve = [[short ciliary nerves|short ciliary]] |
Lymph = |
Action = [[Accommodation reflex|accommodation]]; regulation of [[trabecular meshwork]] pore size |
MeshName = |
MeshNumber = |
DorlandsPre = m_22 |
DorlandsSuf = 12548589 |
}}
}}
The '''ciliary muscle''' is a ring of striated [[smooth muscle]]<ref name="Kleinmann">Kleinmann, Guy MD; Kim, Hee Joon MD; Yee, Richard W. MD (2006). "Scleral Expansion Procedure for the Correction of Presbyopia." (article) {{cite book | title = International Ophthalmology Clinics. 46(3):1-12 | publisher = Lippincott Williams & Wilkins, Inc.}} ISSN: 0020-8167.</ref> in the [[eye]]'s middle layer that controls [[accommodation of the eye|accommodation]] for viewing objects at varying distances and regulates the flow of aqueous humour into [[Schlemm's canal]]. The muscle has [[parasympathetic]] and [[sympathetic]] [[innervation]].
The '''ciliary muscle''' is an [[intrinsic muscle]] of the [[Human eye|eye]] formed as a ring of [[smooth muscle]]<ref name="Kleinmann">{{cite journal |pmid=16929221 |year=2006 |last1=Kleinmann |first1=G |title=Scleral expansion procedure for the correction of presbyopia |journal=International Ophthalmology Clinics |volume=46 |issue=3 |pages=1–12 |last2=Kim |first2=H. J. |last3=Yee |first3=R. W. |doi=10.1097/00004397-200604630-00003 |s2cid=45247729 }}</ref><ref name="Schachar">Schachar, Ronald A. (2012). "Anatomy and Physiology." (Chapter 4) {{cite book | title = The Mechanism of Accommodation and Presbyopia. | publisher = Kugler Publications}} {{ISBN|978-9-062-99233-1}}.</ref> in the eye's middle layer, the [[uvea]] ([[vascular layer]]). It controls [[accommodation of the eye|accommodation]] for viewing objects at varying distances and regulates the flow of [[aqueous humor]] into [[Schlemm's canal]]. It also changes the shape of the lens within the eye but not the size of the pupil<ref>{{cite journal|title=Focusing by shape change in the lens of the eye: a commentary on Young (1801) 'On the mechanism of the eye'|journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences|volume = 370|issue = 1666|pages = 20140308|first=Michael |last=Land|publisher=Philosophical Transactions of the Royal Society B: Biological Sciences|location=School of Life Sciences, University of Sussex, Brighton|date=Apr 19, 2015|pmc = 4360117|pmid = 25750232|doi = 10.1098/rstb.2014.0308}}</ref> which is carried out by the [[sphincter pupillae]] muscle and [[dilator pupillae]].


The [[ciliary muscle]], [[pupillary sphincter muscle]] and [[pupillary dilator muscle]] sometimes are called [[intrinsic ocular muscle]]s<ref>{{cite journal |last1=Kels |first1=Barry D. |last2=Grzybowski |first2=Andrzej |last3=Grant-Kels |first3=Jane M. |title=Human ocular anatomy |journal=Clinics in Dermatology |date=March 2015 |volume=33 |issue=2 |pages=140–146 |doi=10.1016/j.clindermatol.2014.10.006 |pmid=25704934 }}</ref> or [[intraocular muscle]]s.<ref>{{cite book |last1=Ludwig |first1=Parker E. |last2=Aslam |first2=Sanah |last3=Czyz |first3=Craig N. |title=StatPearls |date=2024 |publisher=StatPearls Publishing |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK470534/ |chapter=Anatomy, Head and Neck: Eye Muscles |pmid=29262013 }}</ref>
==Etymology==
The word ''ciliary'' ([[pronunciation]]: 'sil-E-"er-E) had its origins around 1685-1695.<ref>Dictionary.com, "cilia", Dictionary.com Unabridged. Source location: Random House, Inc. <http://dictionary.reference.com/browse/cilia>. Available: http://dictionary.reference.com. Accessed: January 16, 2010</ref> The term ''[[Cilia]]'' originated a few years later in 1705–1715, and is the [[Neo-Latin]] [[plural]] of ''cilium'' meaning [[eyelash]]. In [[Latin]], ''cilia'' means upper [[eyelid]] and is perhaps a [[back formation]] from ''supercilium'', meaning [[eyebrow]]. The suffix ''-ary'' originally occured in loanwords from [[Middle English]] (''-arie''), [[Old French]] (''-er'', ''-eer'', ''-ier'', -''aire'', -er), and Latin (''-ārius''); it can generally mean "pertaining to, connected with," "contributing to," and "for the purpose of."<ref>Dictionary.com, "-ary," in The American Heritage® Dictionary of the English Language, Fourth Edition. Source location: Houghton Mifflin Company, 2004. http://dictionary.reference.com/browse/-ary. Available: http://dictionary.reference.com. Accessed: January 16, 2010.</ref> Taken together, ''cili(a)-ary'' pertains to various anatomical structures in and around the eye, namely the [[ciliary body]] and annular suspension of the the [[lens of the eye]].<ref>Dictionary.com, "ciliary," in Dictionary.com Unabridged. Source location: Random House, Inc. http://dictionary.reference.com/browse/ciliary. Available: http://dictionary.reference.com. Accessed: January 16, 2010.</ref>


==Mode of action==
==Structure==
===Accomodation===
{{main|accommodation of the eye}}
The ciliary fibers have circular, longitudinal (meridional) and radial orientations.<ref>Riordan-Eva Paul, "Chapter 1. Anatomy & Embryology of the Eye" (Chapter). {{cite book | author = Riordan-Eva P, Whitcher JP | title = Vaughan & Asbury's General Ophthalmology | publisher = McGraw-Hill | year = 2008 | edition = 17th}} http://www.accessmedicine.com/content.aspx?aID=3088500.</ref>


===Development===
According to [[Hermann von Helmholtz]]'s theory, the circular ciliary muscle fibers affect [[zonule of Zinn|zonular fibers]] in the [[eye]] (fibers that suspend the [[Lens (anatomy)|lens]] in position during [[accommodation of the eye|accommodation]]), enabling changes in lens shape for light focusing. When the ciliary muscle contracts, it pulls itself forward and moves the frontal region toward the axis of the eye. This releases the tension on the lens caused by the zonular fibers (fibers that hold or flatten the lens). This release of tension of the zonular fibers causes the lens to become more spherical, adapting to short range focus. The other way around, relaxation of the ciliary muscle causes the zonular fibers to become taut, flattening the lens, increasing the [[focal distance]]<ref name="goodman">{{cite book | author = Hardman JG, Limbird LE, Gilman AG | title = Goodman & Gilman's The Pharmacological Basis of Therapeutics | publisher = McGraw-Hill | location = New York | year = 2006 | edition = 11th Edition | chapter = Table 6-1 | pages = 143–145| isbn = 0-07-142280-3 | oclc = | doi = }}</ref>, increasing long range focus. Although Helmholtz's theory has been widely accepted since 1855, its mechanism still remains controverial. Alternative theories of accommodation have been proposed by others, including L. Johnson, M. Tscherning, and Ronald A. Schachar.<ref name=Kleinmann/>
The ciliary muscle develops from [[mesenchyme]] within the [[choroid]] and is considered a cranial [[neural crest]] derivative.<ref name="dudekrw">{{Cite book |last=Dudek |first=Ronald W. |url=https://books.google.com/books?id=MmoJQWsJteoC |title=Embryology |date=2010-04-01 |publisher=Lippincott Williams & Wilkins |isbn=978-1-60547-901-9 |language=en}}</ref>


===Nerve supply===
===Trabecular Meshwork Pore Size===
[[File:Ciliary ganglion pathways.png|thumb|380px|Ciliary [[ganglion]] with parasympathetic fibers of ciliary nerves.]]
Contraction and relaxation of the longitudinal fibers, which insert into the trabecular meshwork in the anterior chamber of the eye, cause an increase and decrease in the meshwork pore size, respectively, facilitating and impeding [[aqueous humour]] flow into the [[canal of Schlemm]].<ref>Salmon John F, "Chapter 11. Glaucoma" (Chapter). {{cite book | author = Riordan-Eva P, Whitcher JP | title = Vaughan & Asbury's General Ophthalmology | publisher = McGraw-Hill | year = 2008 | edition = 17th}} http://www.accessmedicine.com/content.aspx?aID=3089104.</ref>
The ciliary muscle receives parasympathetic fibers from the [[short ciliary nerves]] that arise from the [[ciliary ganglion]]. The parasympathetic postganglionic fibers are part of cranial nerve V<sub>1</sub> ([[Nasociliary nerve|Nasociliary nerve of the trigeminal]]), while presynaptic parasympathetic fibers to the ciliary ganglia travel with the oculomotor nerve.<ref>{{cite book | vauthors = Moore KL, Dalley AF | title = Clinically Oriented Anatomy | chapter = Head (chapter 7) | page = [https://archive.org/details/clinicallyorient00moor_1/page/972 972] | publisher = Lippincott Williams & Wilkins | year = 2006 | edition = 5th | isbn = 0-7817-3639-0 | chapter-url-access = registration | chapter-url = https://archive.org/details/clinicallyorient00moor_1/page/972 }}</ref> The postganglionic parasympathetic innervation arises from the ciliary ganglion.<ref>{{cite journal |last1=McDougal |first1=David H. |last2=Gamlin |first2=Paul D. |title=Autonomic control of the eye |journal=Comprehensive Physiology |date=January 2015 |volume=5 |issue=1 |pages=439–473 |doi=10.1002/cphy.c140014 |pmc=4919817 |pmid=25589275 }}</ref>


Presynaptic parasympathetic signals that originate in the [[Edinger-Westphal nucleus]] are carried by cranial nerve III (the [[oculomotor nerve]]) and travel through the [[ciliary ganglion]] via the postganglionic parasympathetic fibers which travel in the [[short ciliary nerves]] and supply the [[ciliary body]] and iris. [[Parasympathetic]] activation of the M3 [[muscarinic receptors]] causes ciliary muscle contraction. The effect of contraction is to decrease the diameter of the ring of ciliary muscle causing relaxation of the zonule fibers, the lens becomes more spherical, increasing its power to refract light for near vision.{{citation needed|date=December 2016}}
==Innervation==
The ciliary muscle receives both parasympathetic and sympathetic fibers from the [[ciliary ganglion]] called [[short ciliary nerves]]. These postganglionic fibers are part of cranial nerve V<sub>1</sub> (opthalmic branch of the [[trigeminal nerve]])<ref>{{cite book | author = Moore KL, Dalley AF | title = Clinically Oriented Anatomy | chapter = Head (chapter 7) | page = 972| publisher = Lippincott Williams & Wilkins | year = 2006 | edition = 5th | ISBN = 0-7817-3639-0}}</ref>.
[[Image:Ciliary_ganglion_pathways.png|thumb|right|380px|Ciliary [[ganglion]] with sympathetic and parasympathetic fibers of ciliary nerves.]]
Postsynaptic sympathetic signals that orginate in the [[superior cervical ganglion]] are carried by the nasociliary nerve or directly extend from the [[internal carotid plexus]] and pass through the ciliary ganglion. Sympathetic ([[adrenergic]]) activation of the muscle's [[beta-2 receptor]]s result in relaxation and increase in ciliary body size.


The parasympathetic tone is dominant when a higher degree of accommodation of the lens is required, such as reading a book.<ref>{{cite book |editor1-last=Brunton |editor1-first=L. L. |editor2-last=Chabner |editor2-first=Bruce |editor3-last=Knollmann |editor3-first=Björn C. |title=[[Goodman & Gilman's The Pharmacological Basis of Therapeutics]]|edition=12 |location=New York |publisher=McGraw-Hill |year=2011 |isbn=978-0-07-162442-8}}</ref>
Presynaptic parasympathetic signals that originate in the [[Edinger-Westphal nucleus]] are carried by cranial nerve III (the [[oculomotor nerve]]) and synapse on the [[ciliary ganglion]]. [[Parasympathetic]] activation of the M3 [[muscarinic receptors]] causes ciliary muscle contraction and consequent reduction in the size of the ciliary body.


==Function==
The [[adrenergic]] tone is dominant over the parasympathetic tone.<ref name=goodman/>


===Accommodation===
==Role in the Treatment of [[Glaucoma]]==
{{main|accommodation of the eye}}
Open-angle glaucoma (OAG) and closed-angle glaucoma (CAG) may be treated by muscarinic receptor agonists (e.g., [[pilocarpine]]), which cause rapid [[miosis]] and contraction of the ciliary muscles, opening the trabecular meshwork, facilitating drainage of the aqueous humour into the canal of Schlemm and ultimately decreasing [[intraocular pressure]]<ref name="Le">Le, Tao T.; Cai, Xumei; Waples-Trefil, Flora. "QID: 22067". USMLERx. MedIQ Learning, LLC. 2006-2010. 13 Jan. 2010 <http://usmlerx.com>.</ref>.
The ciliary fibers have circular (Ivanoff),<ref>{{cite book |doi=10.1007/978-3-540-69146-4_8 |chapter=Ocular Embryology with Special Reference to Chamber Angle Development |title=The Glaucomas |pages=61–9 |year=2009 |isbn=978-3-540-69144-0 }}</ref> longitudinal ([[meridional]]) and radial orientations.<ref>Riordan-Eva Paul, "Chapter 1. Anatomy & Embryology of the Eye" (Chapter). {{cite book |vauthors=Riordan-Eva P, Whitcher JP | title = Vaughan & Asbury's General Ophthalmology | publisher = McGraw-Hill | year = 2008 | edition = 17th }} [http://www.accessmedicine.com/content.aspx?aID=3088500 AccessMedicine.com] {{webarchive|url=https://web.archive.org/web/20090706124937/http://www.accessmedicine.com/content.aspx?aID=3088500 |date=2009-07-06 }}</ref>


According to [[Hermann von Helmholtz]]'s theory, the circular ciliary muscle fibers affect [[zonule of Zinn|zonular fibers]] in the [[human eye|eye]] (fibers that suspend the [[Lens (anatomy)|lens]] in position during [[accommodation of the eye|accommodation]]), enabling changes in lens shape for light focusing. When the ciliary muscle contracts, it pulls itself forward and moves the frontal region toward the axis of the eye. This releases the tension on the lens caused by the zonular fibers (fibers that hold or flatten the lens). This release of tension of the zonular fibers causes the lens to become more spherical, adapting to short range focus. Conversely, relaxation of the ciliary muscle causes the zonular fibers to become taut, flattening the lens, increasing the [[focal distance]],<ref name="goodman">{{cite book |editor1-first=Laurence L. |editor1-last=Brunton |editor2-first=John S. |editor2-last=Lazo |editor3-first=Keith |editor3-last=Parker |title=[[Goodman & Gilman's The Pharmacological Basis of Therapeutics]] |edition=11th |location=New York |publisher=McGraw-Hill |year=2005 |isbn=978-0-07-162442-8 |pages=134–135}}</ref> increasing long range focus. Although Helmholtz's theory has been widely accepted since 1855, its mechanism still remains controversial. Alternative theories of accommodation have been proposed by others, including L. Johnson, M. Tscherning, and especially Ronald A. Schachar.<ref name=Kleinmann/>
==See also==

*[[Accommodation reflex]]
===Trabecular meshwork pore size===
*[[Ciliary body]]
Contraction and relaxation of the longitudinal fibers, which insert into the [[trabecular meshwork]] in the anterior chamber of the eye, cause an increase and decrease in the meshwork pore size, respectively, facilitating and impeding [[aqueous humour]] flow into the [[canal of Schlemm]].<ref>Salmon John F, "Chapter 11. Glaucoma" (Chapter). {{cite book |vauthors=Riordan-Eva P, Whitcher JP | title = Vaughan & Asbury's General Ophthalmology | publisher = McGraw-Hill | year = 2008 | edition = 17th}} [http://www.accessmedicine.com/content.aspx?aID=3089104 AccessMedicine.com] {{webarchive|url=https://web.archive.org/web/20090706124959/http://www.accessmedicine.com/content.aspx?aID=3089104 |date=2009-07-06 }}</ref>
*[[Cycloplegia]]

*[[Presbyopia]]
==Clinical significance==

===Glaucoma===
Open-angle [[glaucoma]] (OAG) and closed-angle glaucoma (CAG) may be treated by muscarinic receptor agonists (e.g., [[pilocarpine]]), which cause rapid [[miosis]] and contraction of the ciliary muscles, opening the trabecular meshwork, facilitating drainage of the aqueous humour into the canal of Schlemm and ultimately decreasing [[intraocular pressure]].<ref name="Le">Le, Tao T.; Cai, Xumei; Waples-Trefil, Flora. "QID: 22067". USMLERx. MedIQ Learning, LLC. 2006–2010. 13 January 2010 [http://usmlerx.com Usmlerx.com] {{Webarchive|url=https://web.archive.org/web/20121026042853/http://www.usmlerx.com/ |date=2012-10-26 }}</ref>

==History==

===Etymology===
The word ''ciliary'' had its origins around 1685–1695.<ref>"cilia", Unabridged. Source location: Random House, Inc. Reference.com. Retrieved on 2010-01-16 from http://dictionary.reference.com/browse/cilia.</ref> The term ''[[cilia]]'' originated a few years later in 1705–1715, and is the [[Neo-Latin]] [[plural]] of ''cilium'' meaning [[eyelash]]. In [[Latin]], ''cilia'' means upper [[eyelid]] and is perhaps a [[back formation]] from ''supercilium'', meaning [[eyebrow]]. The suffix ''-ary'' originally occurred in loanwords from [[Middle English]] (''-arie''), [[Old French]] (''-er'', ''-eer'', ''-ier'', -''aire'', -er), and Latin (''-ārius''); it can generally mean "pertaining to, connected with", "contributing to", and "for the purpose of".<ref>Dictionary.com, "-ary", in The American Heritage Dictionary of the English Language, Fourth Edition. Source location: Houghton Mifflin Company, 2004. Reference.com. Retrieved on 2010-01-16 from http://dictionary.reference.com/browse/-ary.</ref> Taken together, ''cili(a)-ary'' pertains to various anatomical structures in and around the eye, namely the [[ciliary body]] and annular suspension of the [[lens of the eye]].<ref>"ciliary," in Dictionary.com Unabridged. Source location: Random House, Inc. Reference.com. Retrieved on 2010-01-16 from http://dictionary.reference.com/browse/ciliary.</ref>


==Additional images==
==Additional images==
<gallery>
<gallery>
File:Gray873.png|The arteries of the choroid and iris. The greater part of the sclera has been removed.
<Image:Gray840.png|Sympathetic connections of the ciliary and superior cervical ganglia.>
File:Gray878.png|Iris, front view.
Image:Gray873.png|The arteries of the choroid and iris. The greater part of the sclera has been removed.
Image:Gray878.png|Iris, front view.
</gallery>
</gallery>

==See also==
{{Anatomy-terms}}
* [[Accommodation reflex]]
* [[Cycloplegia]]
* [[Extraocular muscle]]
* [[Presbyopia]]


==References==
==References==
{{Reflist|2}}
{{Reflist}}


==External links==
==External links==
* [http://dspace.udel.edu:8080/dspace/handle/19716/1723 Lens, zonule fibers, and ciliary muscles—SEM] {{Webarchive|url=https://web.archive.org/web/20110928214726/http://dspace.udel.edu:8080/dspace/handle/19716/1723 |date=2011-09-28 }}
* {{eMedicineDictionary|Ciliary+muscle}}
* Lens, zonule fibers, and ciliary muscles -- SEM <http://dspace.udel.edu:8080/dspace/handle/19716/1723>


{{Eye}}
{{Eye}}
{{Visual system}}
{{Authority control}}


{{DEFAULTSORT:Ciliary Muscle}}
[[Category:Muscles of the head and neck]]
[[Category:Muscles of the head and neck]]
[[Category:Eye]]
[[Category:Human eye anatomy]]


[[es:Músculo ciliar]]
[[eu:Gihar ziliar]]
[[hr:Cilijarni mišić]]
[[it:Muscolo ciliare]]
[[hu:Musculus ciliaris]]
[[pl:Mięsień rzęskowy]]
[[pt:Músculo ciliar]]
[[ru:Цилиарная мышца]]
[[sk:Vráskovec]]
[[sr:Цилијарни мишић]]
[[sh:Cilijarni mišić]]
[[sv:Ciliarmuskeln]]
[[th:กล้ามเนื้อซิลิอารี]]

Latest revision as of 19:24, 14 September 2024

Ciliary muscle
The choroid and iris. (Ciliary muscle is labeled near top.)
Details
PronunciationUK: /ˈsɪliəri/, US: /ˈsɪliɛri/[2]
Origin1) longitudinal fibers → scleral spur; 2) circular fibers → encircle root of iris[1]
Insertion1) longitudinal fibers → ciliary process, 2) circular fibers → encircle root of iris[1]
ArteryLong posterior ciliary arteries
VeinVorticose veins
NerveShort ciliary
Parasympathetic fibers in the oculomotor nerve (CN-III) synapse in the ciliary ganglion. Parasympathetic postganglionic fibers from the ciliary ganglion travel through short ciliary nerves into the ocular globe.
Actions1) Accommodation, 2) regulation of trabecular meshwork pore sizes
Identifiers
Latinmusculus ciliaris
TA98A15.2.03.014
TA26770
FMA49151
Anatomical terms of muscle

The ciliary muscle is an intrinsic muscle of the eye formed as a ring of smooth muscle[3][4] in the eye's middle layer, the uvea (vascular layer). It controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humor into Schlemm's canal. It also changes the shape of the lens within the eye but not the size of the pupil[5] which is carried out by the sphincter pupillae muscle and dilator pupillae.

The ciliary muscle, pupillary sphincter muscle and pupillary dilator muscle sometimes are called intrinsic ocular muscles[6] or intraocular muscles.[7]

Structure

[edit]

Development

[edit]

The ciliary muscle develops from mesenchyme within the choroid and is considered a cranial neural crest derivative.[8]

Nerve supply

[edit]
Ciliary ganglion with parasympathetic fibers of ciliary nerves.

The ciliary muscle receives parasympathetic fibers from the short ciliary nerves that arise from the ciliary ganglion. The parasympathetic postganglionic fibers are part of cranial nerve V1 (Nasociliary nerve of the trigeminal), while presynaptic parasympathetic fibers to the ciliary ganglia travel with the oculomotor nerve.[9] The postganglionic parasympathetic innervation arises from the ciliary ganglion.[10]

Presynaptic parasympathetic signals that originate in the Edinger-Westphal nucleus are carried by cranial nerve III (the oculomotor nerve) and travel through the ciliary ganglion via the postganglionic parasympathetic fibers which travel in the short ciliary nerves and supply the ciliary body and iris. Parasympathetic activation of the M3 muscarinic receptors causes ciliary muscle contraction. The effect of contraction is to decrease the diameter of the ring of ciliary muscle causing relaxation of the zonule fibers, the lens becomes more spherical, increasing its power to refract light for near vision.[citation needed]

The parasympathetic tone is dominant when a higher degree of accommodation of the lens is required, such as reading a book.[11]

Function

[edit]

Accommodation

[edit]
Main article: accommodation of the eye

The ciliary fibers have circular (Ivanoff),[12] longitudinal (meridional) and radial orientations.[13]

According to Hermann von Helmholtz's theory, the circular ciliary muscle fibers affect zonular fibers in the eye (fibers that suspend the lens in position during accommodation), enabling changes in lens shape for light focusing. When the ciliary muscle contracts, it pulls itself forward and moves the frontal region toward the axis of the eye. This releases the tension on the lens caused by the zonular fibers (fibers that hold or flatten the lens). This release of tension of the zonular fibers causes the lens to become more spherical, adapting to short range focus. Conversely, relaxation of the ciliary muscle causes the zonular fibers to become taut, flattening the lens, increasing the focal distance,[14] increasing long range focus. Although Helmholtz's theory has been widely accepted since 1855, its mechanism still remains controversial. Alternative theories of accommodation have been proposed by others, including L. Johnson, M. Tscherning, and especially Ronald A. Schachar.[3]

Trabecular meshwork pore size

[edit]

Contraction and relaxation of the longitudinal fibers, which insert into the trabecular meshwork in the anterior chamber of the eye, cause an increase and decrease in the meshwork pore size, respectively, facilitating and impeding aqueous humour flow into the canal of Schlemm.[15]

Clinical significance

[edit]

Glaucoma

[edit]

Open-angle glaucoma (OAG) and closed-angle glaucoma (CAG) may be treated by muscarinic receptor agonists (e.g., pilocarpine), which cause rapid miosis and contraction of the ciliary muscles, opening the trabecular meshwork, facilitating drainage of the aqueous humour into the canal of Schlemm and ultimately decreasing intraocular pressure.[16]

History

[edit]

Etymology

[edit]

The word ciliary had its origins around 1685–1695.[17] The term cilia originated a few years later in 1705–1715, and is the Neo-Latin plural of cilium meaning eyelash. In Latin, cilia means upper eyelid and is perhaps a back formation from supercilium, meaning eyebrow. The suffix -ary originally occurred in loanwords from Middle English (-arie), Old French (-er, -eer, -ier, -aire, -er), and Latin (-ārius); it can generally mean "pertaining to, connected with", "contributing to", and "for the purpose of".[18] Taken together, cili(a)-ary pertains to various anatomical structures in and around the eye, namely the ciliary body and annular suspension of the lens of the eye.[19]

Additional images

[edit]
  • The arteries of the choroid and iris. The greater part of the sclera has been removed.
    The arteries of the choroid and iris. The greater part of the sclera has been removed.
  • Iris, front view.
    Iris, front view.

See also

[edit]
This article uses anatomical terminology.

References

[edit]
  1. ^ a b Gest, Thomas R; Burkel, William E. "Anatomy Tables - Eye." Medical Gross Anatomy. 2000. University of Michigan Medical School. January 5, 2010 Umich.edu Archived 2010-05-26 at the Wayback Machine
  2. ^ Wells, John C. (2008). Longman Pronunciation Dictionary (3rd ed.). Longman. ISBN 978-1-4058-8118-0.
  3. ^ a b Kleinmann, G; Kim, H. J.; Yee, R. W. (2006). "Scleral expansion procedure for the correction of presbyopia". International Ophthalmology Clinics. 46 (3): 1–12. doi:10.1097/00004397-200604630-00003. PMID 16929221. S2CID 45247729.
  4. ^ Schachar, Ronald A. (2012). "Anatomy and Physiology." (Chapter 4) The Mechanism of Accommodation and Presbyopia. Kugler Publications. ISBN 978-9-062-99233-1.
  5. ^ Land, Michael (Apr 19, 2015). "Focusing by shape change in the lens of the eye: a commentary on Young (1801) 'On the mechanism of the eye'". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 370 (1666). School of Life Sciences, University of Sussex, Brighton: Philosophical Transactions of the Royal Society B: Biological Sciences: 20140308. doi:10.1098/rstb.2014.0308. PMC 4360117. PMID 25750232.
  6. ^ Kels, Barry D.; Grzybowski, Andrzej; Grant-Kels, Jane M. (March 2015). "Human ocular anatomy". Clinics in Dermatology. 33 (2): 140–146. doi:10.1016/j.clindermatol.2014.10.006. PMID 25704934.
  7. ^ Ludwig, Parker E.; Aslam, Sanah; Czyz, Craig N. (2024). "Anatomy, Head and Neck: Eye Muscles". StatPearls. StatPearls Publishing. PMID 29262013.
  8. ^ Dudek, Ronald W. (2010-04-01). Embryology. Lippincott Williams & Wilkins. ISBN 978-1-60547-901-9.
  9. ^ Moore KL, Dalley AF (2006). "Head (chapter 7)". Clinically Oriented Anatomy (5th ed.). Lippincott Williams & Wilkins. p. 972. ISBN 0-7817-3639-0.
  10. ^ McDougal, David H.; Gamlin, Paul D. (January 2015). "Autonomic control of the eye". Comprehensive Physiology. 5 (1): 439–473. doi:10.1002/cphy.c140014. PMC 4919817. PMID 25589275.
  11. ^ Brunton, L. L.; Chabner, Bruce; Knollmann, Björn C., eds. (2011). Goodman & Gilman's The Pharmacological Basis of Therapeutics (12 ed.). New York: McGraw-Hill. ISBN 978-0-07-162442-8.
  12. ^ "Ocular Embryology with Special Reference to Chamber Angle Development". The Glaucomas. 2009. pp. 61–9. doi:10.1007/978-3-540-69146-4_8. ISBN 978-3-540-69144-0.
  13. ^ Riordan-Eva Paul, "Chapter 1. Anatomy & Embryology of the Eye" (Chapter). Riordan-Eva P, Whitcher JP (2008). Vaughan & Asbury's General Ophthalmology (17th ed.). McGraw-Hill. AccessMedicine.com Archived 2009-07-06 at the Wayback Machine
  14. ^ Brunton, Laurence L.; Lazo, John S.; Parker, Keith, eds. (2005). Goodman & Gilman's The Pharmacological Basis of Therapeutics (11th ed.). New York: McGraw-Hill. pp. 134–135. ISBN 978-0-07-162442-8.
  15. ^ Salmon John F, "Chapter 11. Glaucoma" (Chapter). Riordan-Eva P, Whitcher JP (2008). Vaughan & Asbury's General Ophthalmology (17th ed.). McGraw-Hill. AccessMedicine.com Archived 2009-07-06 at the Wayback Machine
  16. ^ Le, Tao T.; Cai, Xumei; Waples-Trefil, Flora. "QID: 22067". USMLERx. MedIQ Learning, LLC. 2006–2010. 13 January 2010 Usmlerx.com Archived 2012-10-26 at the Wayback Machine
  17. ^ "cilia", Unabridged. Source location: Random House, Inc. Reference.com. Retrieved on 2010-01-16 from http://dictionary.reference.com/browse/cilia.
  18. ^ Dictionary.com, "-ary", in The American Heritage Dictionary of the English Language, Fourth Edition. Source location: Houghton Mifflin Company, 2004. Reference.com. Retrieved on 2010-01-16 from http://dictionary.reference.com/browse/-ary.
  19. ^ "ciliary," in Dictionary.com Unabridged. Source location: Random House, Inc. Reference.com. Retrieved on 2010-01-16 from http://dictionary.reference.com/browse/ciliary.
[edit]
Retrieved from "https://en.wikipedia.org/enwiki/w/index.php?title=Ciliary_muscle&oldid=1245734641"