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Ciliary muscle

November 13, 2023

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, 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.

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 vein
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
[edit on Wikidata]

Structure edit

Development edit

The ciliary muscle develops from mesenchyme within the choroid and is considered a cranial neural crest derivative.[6]

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.[7] The postganglionic parasympathetic innervation arises from the ciliary ganglion.[8]

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.[9]

Function edit

Accommodation edit

Main article: accommodation of the eye

The ciliary fibers have circular (Ivanoff),[10] longitudinal (meridional) and radial orientations.[11]

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,[12] 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.[13]

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.[14]

History edit

Etymology edit

The word ciliary had its origins around 1685–1695.[15] 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".[16] 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.[17]

Additional images edit

  •  

    The arteries of the choroid and iris. The greater part of the sclera has been removed.

  •  

    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 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. School of Life Sciences, University of Sussex, Brighton: Philosophical Transactions of the Royal Society B: Biological Sciences. 370 (1666): 20140308. doi:10.1098/rstb.2014.0308. PMC 4360117. PMID 25750232.
  6. ^ Dudek, Ronald W. (2010-04-01). Embryology. Lippincott Williams & Wilkins. ISBN 978-1-60547-901-9.
  7. ^ Moore KL, Dalley AF (2006). "Head (chapter 7)". Clinically Oriented Anatomy (5th ed.). Lippincott Williams & Wilkins. p. 972. ISBN 0-7817-3639-0.
  8. ^ McDougal, David H.; Gamlin, Paul D. (January 2015). "Autonomic control of the eye". Comprehensive Physiology. 5 (1): 439–473. doi:10.1002/cphy.c140014. ISSN 2040-4603. PMC 4919817. PMID 25589275.
  9. ^ 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.
  10. ^ "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.
  11. ^ 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 2009-07-06 at the Wayback Machine
  12. ^ 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.
  13. ^ Salmon John F, "Chapter 11. Glaucoma" (Chapter). Riordan-Eva P, Whitcher JP (2008). Vaughan & Asbury's General Ophthalmology (17th ed.). McGraw-Hill. AccessMedicine.com 2009-07-06 at the Wayback Machine
  14. ^ Le, Tao T.; Cai, Xumei; Waples-Trefil, Flora. "QID: 22067". USMLERx. MedIQ Learning, LLC. 2006–2010. 13 January 2010 Usmlerx.com 2012-10-26 at the Wayback Machine
  15. ^ "cilia", Unabridged. Source location: Random House, Inc. Reference.com. Retrieved on 2010-01-16 from http://dictionary.reference.com/browse/cilia.
  16. ^ 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.
  17. ^ "ciliary," in Dictionary.com Unabridged. Source location: Random House, Inc. Reference.com. Retrieved on 2010-01-16 from http://dictionary.reference.com/browse/ciliary.

External links edit

  • Lens, zonule fibers, and ciliary muscles—SEM 2011-09-28 at the Wayback Machine

November 13, 2023
ciliary, muscle, ciliary, muscle, intrinsic, muscle, formed, ring, smooth, muscle, middle, layer, uvea, vascular, layer, controls, accommodation, viewing, objects, varying, distances, regulates, flow, aqueous, humor, into, schlemm, canal, also, changes, shape,. 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 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 Ciliary muscleThe choroid and iris Ciliary muscle is labeled near top DetailsPronunciationUK ˈ s ɪ l i e r i US ˈ s ɪ l i ɛr i 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 arteriesVeinVorticose veinNerveshort ciliaryParasympathetic 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 sizesIdentifiersLatinmusculus ciliarisTA98A15 2 03 014TA26770FMA49151Anatomical terms of muscle edit on Wikidata Contents 1 Structure 1 1 Development 1 2 Nerve supply 2 Function 2 1 Accommodation 2 2 Trabecular meshwork pore size 3 Clinical significance 3 1 Glaucoma 4 History 4 1 Etymology 5 Additional images 6 See also 7 References 8 External linksStructure editDevelopment edit The ciliary muscle develops from mesenchyme within the choroid and is considered a cranial neural crest derivative 6 Nerve supply edit nbsp 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 7 The postganglionic parasympathetic innervation arises from the ciliary ganglion 8 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 9 Function editAccommodation edit Main article accommodation of the eye The ciliary fibers have circular Ivanoff 10 longitudinal meridional and radial orientations 11 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 12 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 13 Clinical significance editGlaucoma 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 14 History editEtymology edit The word ciliary had its origins around 1685 1695 15 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 arius it can generally mean pertaining to connected with contributing to and for the purpose of 16 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 17 Additional images edit nbsp The arteries of the choroid and iris The greater part of the sclera has been removed nbsp Iris front view See also editThis article uses anatomical terminology Accommodation reflex Cycloplegia Extraocular muscle PresbyopiaReferences edit 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 Wells John C 2008 Longman Pronunciation Dictionary 3rd ed Longman ISBN 978 1 4058 8118 0 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 Schachar Ronald A 2012 Anatomy and Physiology Chapter 4 The Mechanism of Accommodation and Presbyopia Kugler Publications ISBN 978 9 062 99233 1 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 School of Life Sciences University of Sussex Brighton Philosophical Transactions of the Royal Society B Biological Sciences 370 1666 20140308 doi 10 1098 rstb 2014 0308 PMC 4360117 PMID 25750232 Dudek Ronald W 2010 04 01 Embryology Lippincott Williams amp Wilkins ISBN 978 1 60547 901 9 Moore KL Dalley AF 2006 Head chapter 7 Clinically Oriented Anatomy 5th ed Lippincott Williams amp Wilkins p 972 ISBN 0 7817 3639 0 McDougal David H Gamlin Paul D January 2015 Autonomic control of the eye Comprehensive Physiology 5 1 439 473 doi 10 1002 cphy c140014 ISSN 2040 4603 PMC 4919817 PMID 25589275 Brunton L L Chabner Bruce Knollmann Bjorn C eds 2011 Goodman amp Gilman s The Pharmacological Basis of Therapeutics 12 ed New York McGraw Hill ISBN 978 0 07 162442 8 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 Riordan Eva Paul Chapter 1 Anatomy amp Embryology of the Eye Chapter Riordan Eva P Whitcher JP 2008 Vaughan amp Asbury s General Ophthalmology 17th ed McGraw Hill AccessMedicine com Archived 2009 07 06 at the Wayback Machine Brunton Laurence L Lazo John S Parker Keith eds 2005 Goodman amp Gilman s The Pharmacological Basis of Therapeutics 11th ed New York McGraw Hill pp 134 135 ISBN 978 0 07 162442 8 Salmon John F Chapter 11 Glaucoma Chapter Riordan Eva P Whitcher JP 2008 Vaughan amp Asbury s General Ophthalmology 17th ed McGraw Hill AccessMedicine com Archived 2009 07 06 at the Wayback Machine 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 cilia Unabridged Source location Random House Inc Reference com Retrieved on 2010 01 16 from http dictionary reference com browse cilia 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 ciliary in Dictionary com Unabridged Source location Random House Inc Reference com Retrieved on 2010 01 16 from http dictionary reference com browse ciliary External links editLens zonule fibers and ciliary muscles SEM Archived 2011 09 28 at the Wayback Machine Retrieved from https en wikipedia org w index php title Ciliary muscle amp oldid 1173781794, wikipedia, wiki, book, books, library,

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