Ciliary muscle

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Ciliary muscle
The choroid and iris. (Ciliary muscle is labeled near top.)
Latin musculus ciliaris
Origin 1) longitudinal fibers → scleral spur; 2) circular fibers → encircle root of iris[1]
Insertion 1) longitudinal fibers → ciliary process, 2) circular fibers → encircle root of iris[1]
long posterior ciliary arteries
Vorticose vein
short ciliary
From oculomotor nerve
Through ciliary ganglion
Actions 1) accommodation, 2) regulation of trabecular meshwork pore size
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Anatomical terms of muscle
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The ciliary muscle /ˈsɪli.ɛəri/ is a ring of smooth muscle[2][3] in the eye's middle layer (vascular layer) that controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humour into Schlemm's canal. It changes the shape of the lens within the eye, not the size of the pupil which is carried out by the sphincter pupillae muscle and dilator pupillae.



The ciliary muscle develops from the mesenchyme within the choroid[4] and is considered a cranial neural crest derivative.


The ciliary muscle receives only parasympathetic fibers from the short ciliary nerves that arise from the ciliary ganglion. These postganglionic fibers are part of cranial nerve III (Oculomotor nerve).[5]

Ciliary ganglion with parasympathetic fibers of ciliary nerves.

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. 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. The zonule fibers relax and the lens becomes more spherical, increasing its power to refract light for near vision.

The parasympathetic tone is dominant when a higher degree of accommodation of the lens is required, such as reading a book.[6]



The ciliary fibers have circular (Ivanoff),[7] longitudinal (meridional) and radial orientations.[8]

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. The other way around, relaxation of the ciliary muscle causes the zonular fibers to become taut, flattening the lens, increasing the focal distance,[9] 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 Ronald A. Schachar.[2]

Trabecular meshwork pore size

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.[10]

Clinical significance


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.[11]



The word ciliary had its origins around 1685–1695.[12] 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."[13] 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.[14]

Additional images

See also


  1. 1.0 1.1 Gest, Thomas R; Burkel, William E. "Anatomy Tables - Eye." Medical Gross Anatomy. 2000. University of Michigan Medical School. January 5, 2010
  2. 2.0 2.1 Kleinmann, G; Kim, H. J.; Yee, R. W. (2006). "Scleral expansion procedure for the correction of presbyopia". International ophthalmology clinics. 46 (3): 1–12. PMID 16929221.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  3. Schachar, Ronald A. (2012). "Anatomy and Physiology." (Chapter 4) The Mechanism of Accommodation and Presbyopia. Kugler Publications.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles> ISBN 978-9-062-99233-1.
  4. Dudek RW, Fix JD (2004). "Eye" (chapter 9). Embryology - Board Review Series (3rd edition, illustrated). Lippincott Williams & Wilkins. p. 92. ISBN 0-7817-5726-6, ISBN 978-0-7817-5726-3., Retrieved January 17, 2010.
  5. Moore KL, Dalley AF (2006). "Head (chapter 7)". Clinically Oriented Anatomy (5th ed.). Lippincott Williams & Wilkins. p. 972. ISBN 0-7817-3639-0.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  6. 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.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  7. "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.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  8. 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.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  9. 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.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  10. Salmon John F, "Chapter 11. Glaucoma" (Chapter). Riordan-Eva P, Whitcher JP (2008). Vaughan & Asbury's General Ophthalmology (17th ed.). McGraw-Hill.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  11. Le, Tao T.; Cai, Xumei; Waples-Trefil, Flora. "QID: 22067". USMLERx. MedIQ Learning, LLC. 2006–2010. 13 January 2010
  12. "cilia", Unabridged. Source location: Random House, Inc., Accessed: January 16, 2010
  13., "-ary," in The American Heritage Dictionary of the English Language, Fourth Edition. Source location: Houghton Mifflin Company, 2004., Accessed: January 16, 2010.
  14. "ciliary," in Unabridged. Source location: Random House, Inc., Accessed: January 16, 2010.

External links