Editing Ciliary body

{{short description|Part of the eye}}
{{Infobox anatomy
| Name        = Ciliary body
| Latin       = corpus ciliare
| Image       = Blausen 0390 EyeAnatomy Sectional.png
| Caption     = Anterior part of the [[human eye]], with ciliary body near bottom.
| Image2      =
| Caption2    =
| Precursor   =
| System      = [[Visual system]]
| part_of = [[Eye]]
| Artery      = [[Ciliary arteries|long and short posterior ciliary arteries]]
| Vein        =
| Nerve       =
| Lymph       =
}}
The '''ciliary body''' is a part of the [[eye]] that includes the [[ciliary muscle]], which controls the shape of the lens, and the ciliary epithelium, which produces the [[aqueous humor]]. The aqueous humor is produced in the non-pigmented portion of the ciliary body.<ref>{{cite book | last1=Standring | first1=Susan | last2=Gray | first2=Henry | title=Gray's anatomy : the anatomical basis of clinical practice | publisher=Churchill Livingstone/Elsevier | publication-place=[Edinburgh] | date=2008 | isbn=978-0-443-06684-9 | oclc=213447727 }}</ref> The ciliary body is part of the [[uvea]], the layer of tissue that delivers [[oxygen]] and nutrients to the eye tissues. The ciliary body joins the [[ora serrata]] of the [[choroid]] to the root of the [[iris (anatomy)|iris]].<ref name="Cassin">Cassin, B. and Solomon, S. ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing Company, 1990.</ref>

==Structure==
The ciliary body is a ring-shaped thickening of tissue inside the [[eye]] that divides the [[Posterior chamber of eyeball|posterior chamber]] from the [[vitreous body]].  It contains the [[ciliary muscle]], vessels, and fibrous connective tissue.  Folds on the inner ciliary epithelium are called [[ciliary processes]], and these secrete aqueous humor into the posterior chamber. The aqueous humor then flows through the iris into the anterior chamber.<ref>Lang, G. ''Ophthalmology: A Pocket Textbook Atlas, 2 ed.''. Pg. 207. Ulm, Germany. 2007.</ref>

The ciliary body is attached to the lens by [[connective tissue]] called the [[Zonule of Zinn]] (fibers of Zinn). Relaxation of the ciliary muscle puts tension on these fibers and changes the shape of the lens in order to [[Focus (optics)|focus]] [[light]] on the retina.

The inner layer is transparent and covers the [[vitreous body]], and is continuous from the neural tissue of the [[retina]]. The outer layer is highly pigmented, continuous with the [[retinal pigment epithelium]], and constitutes the cells of the [[iris dilator muscle|dilator muscle]]. This double membrane is often considered continuous with the retina and a rudiment of the embryological correspondent to the retina. The inner layer is unpigmented until it reaches the [[iris (anatomy)|iris]], where it takes on pigment. The retina ends at the [[ora serrata]].

The space between the ciliary body and the base of the iris is the ciliary [[Sulcus (morphology)|sulcus]].<ref>Schnaudigel OE. Anatomie des Sulcus ciliaris [Anatomy of the ciliary sulcus]. Fortschr Ophthalmol. 1990;87(4):388-9. German. PMID 2210569.</ref> 

===Nerve supply===
[[File:Ciliary ganglion pathways.png|thumb|right|380px|Ciliary [[ganglion]] with parasympathetic fibers of ciliary nerves.]]
The parasympathetic innervation of the ciliary body is the most clearly understood.  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]].  Postsynaptic fibers from the ciliary ganglion form the short ciliary nerves.  [[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.<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 parasympathetic tone is dominant when a higher degree of accommodation of the lens is required, such as reading a book.<ref>{{cite book |first1=Ryan E. |last1=Hibbs |first2=Alexander C. |last2=Zambon |chapter=Agents Acting at the Neuromuscular Junction and Autonomic Ganglia |chapter-url=http://accesspharmacy.mhmedical.com/content.aspx?bookid=374&sectionid=41266217&jumpsectionID=41268392 |editor1-first=Laurence L. |editor1-last=Brunton |editor2-first=Bruce A. |editor2-last=Chabner |editor3-first=Björn C. |editor3-last=Knollmann |title=Goodman & Gilman's The Pharmacological Basis of Therapeutics |publisher=McGraw-Hill |year=2011 |edition=12th |isbn=978-0-07-162442-8 |title-link=Goodman & Gilman's The Pharmacological Basis of Therapeutics |access-date=2015-05-22 |archive-date=2016-03-03 |archive-url=https://web.archive.org/web/20160303220848/http://accesspharmacy.mhmedical.com/content.aspx?bookid=374&sectionid=41266217&jumpsectionID=41268392 |url-status=dead }}</ref>

The ciliary body is also known to receive sympathetic innervation via long ciliary nerves.<ref>{{cite journal |pmid=4198985 |year=1973 |last1=Ruskell |first1=G. L. |title=Sympathetic innervation of the ciliary muscle in monkeys |journal=Experimental Eye Research |volume=16 |issue=3 |pages=183–90 |doi=10.1016/0014-4835(73)90212-1}}</ref>  When test subjects are startled, their eyes automatically adjust for distance vision.<ref name=pmid13823443>{{cite journal |doi=10.1016/0002-9394(59)90269-7 |pmid=13823443 |title=Autonomic Innervation of the Ciliary Body: A Modified Theory of Accommodation |journal=American Journal of Ophthalmology |volume=48 |issue=3 |pages=287–93 |year=1959 |last1=Fleming |first1=David G. |last2=Hall |first2=James L. }}</ref>

==Function==
The ciliary body has three functions: [[accommodation (eye)|accommodation]], [[aqueous humor]] production, and [[resorption]], and maintenance of the lens zonules for the purpose of anchoring the lens in place.

===Accommodation===
Accommodation essentially means that when the ciliary muscle contracts, the lens becomes more convex, generally improving the focus for closer objects. When it relaxes, it flattens the lens, generally improving the focus for farther objects.

===Aqueous humor===
The ciliary epithelium of the ciliary processes produces [[aqueous humor]], which is responsible for providing oxygen, nutrients, and metabolic waste removal to the lens and the [[cornea]], which do not have their own blood supply. Approximately 80% of aqueous humor production is carried out through active secretion mechanisms (the Na+K+ATPase enzyme creating an osmotic gradient for the passage of water into the posterior chamber) and twenty percent is produced through the ultrafiltration of plasma. [[Intraocular pressure]] affects the rate of ultrafiltration, but not secretion.<ref>{{cite journal |doi=10.1093/bjaceaccp/mkn015 |title=Intraocular pressure |journal=Continuing Education in Anaesthesia, Critical Care & Pain |volume=8 |issue=3 |pages=100–3 |year=2008 |last1=Murgatroyd |first1=H. |last2=Bembridge |first2=J. |doi-access=free }}</ref>

===Lens zonules===
The zonular fibers collectively make up the suspensory ligament of the lens. These provide strong attachments between the ciliary muscle and the capsule of the lens.

==Clinical significance==
[[Glaucoma]] is a group of ocular disorders characterized by high [[intraocular pressure]]-associated neuropathies.<ref>{{cite journal |doi=10.1111/j.1442-9071.2012.02773.x |url=https://zenodo.org/record/1065544 |pmid=22356435 |title=Definition of glaucoma: Clinical and experimental concepts |journal=Clinical & Experimental Ophthalmology |volume=40 |issue=4 |pages=341–9 |year=2012 |last1=Casson |first1=Robert J |last2=Chidlow |first2=Glyn |last3=Wood |first3=John PM |last4=Crowston |first4=Jonathan G |last5=Goldberg |first5=Ivan |doi-access=free |hdl=2440/73277 |hdl-access=free }}</ref> Intraocular pressure depends on the levels of production and resorption of aqueous humor. Because the ciliary body produces aqueous humor, it is the main target of many medications against [[glaucoma]]. Its inhibition leads to the lowering of aqueous humor production and causes a subsequent drop in the [[intraocular pressure]]. There 3 main types of medication affecting the ciliary body:<ref>{{cite web |title=Glaucoma Medications and Their Side Effects |date=10 January 2024 |publisher=Glaucoma Research Foundation |url=http://www.glaucoma.org/treatment/glaucoma-medications-and-their-side-effects.php}}</ref><ref>{{cite web |title=Medication Guide |publisher=Glaucoma Research Foundation |url=http://www.glaucoma.org/treatment/medication-guide.php}}</ref>
*[[Beta blockers]], the second most common treatment method for glaucoma, reduce the production of aqueous humor. They are relatively inexpensive and are available in generic form. [[Timolol]], [[Levobunolol]], and [[Betaxolol]] are common beta blockers prescribed to treat glaucoma.
*[[Alpha-adrenergic agonist]]s work by decreasing production of fluid and increasing drainage. [[Brimonidine]] and [[Apraclonidine]] are two commonly prescribes alpha agonists for glaucoma treatment. Alphagan P uses a purite preservative, which is better tolerated by those who have allergic reactions than the older BAK preservative in other eye drops.<ref>{{Cite news|url=https://www.reviewofophthalmology.com/article/the-pros-and-cons-of-preservatives|title=The Pros and Cons of Preservatives|last=Colo.|first=Malik Y. Kahook, MD, Aurora|access-date=2017-03-13}}</ref> Furthermore, less selective alpha agonists such as [[epinephrine]] may decrease the production of aqueous humor through vasoconstriction of the ciliary body (only for open-angle glaucoma).{{citation needed|date=May 2015}}
*[[Carbonic anhydrase inhibitors]] also decrease fluid production. They are available as eye drops ([[Trusopt]] and [[Azopt]]) and pills ([[Diamox]] and [[Neptazane]]). This may be helpful if using more than one type of eye medication.{{citation needed|date=May 2015}}

==See also==
*[[Intraocular pressure]]
*[[Iridodialysis]]
*[[Glaucoma]]
*[[Cyclodestruction]]

==References==
{{Reflist}}

==External links==
* {{BUHistology|08011loa}}
* {{UMichAtlas|eye_1}} - "Sagittal Section Through the Eyeball"

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[[Category:Human eye anatomy]]