Choroid
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224066001
2008-07-07T04:03:29Z
69.136.109.247
/* Blood supply */
{{Infobox Anatomy |
Name = Choroid |
Latin = choroidea |
GraySubject = 225 |
GrayPage = 1009 |
Image = Schematic diagram of the human eye en.svg |
Caption = Schematic cross section of the human eye; choroid is shown in purple. |
Image2 = Gray875.png |
Caption2 = Interior of anterior half of bulb of eye. (Choroid labeled at right, second from the bottom.) |
Artery = [[short posterior ciliary arteries]], [[long posterior ciliary arteries]] |
System = |
Precursor = |
MeshName = Choroid |
MeshNumber = A09.371.894.223 |
DorlandsPre = c_32 |
DorlandsSuf = 12237606 |
}}
The '''choroid''', also known as the '''choroidea''' or '''choroid coat''', is the [[Blood vessel|vascular]] layer of the [[eye]] lying between the [[retina]] and the [[sclera]]. In humans its thickness is about 0.5 mm. The choroid provides [[oxygen]] and nourishment to the outer layers of the retina [http://www.eyeglossary.net/#C]. Along with the [[ciliary body]] and [[Iris (anatomy)|iris]], the choroid forms the [[uvea (anatomy)|uveal tract]].
==Layers==
The structure of the choroid is generally divided into four layers:
*[[Haller's layer]] - outermost layer of the choroid consisting of larger diameter blood vessels
*[[Sattler's layer]] - layer of medium diameter blood vessels
*[[Choriocapillaris]] - layer of capillaries
*[[Bruch's membrane]] (synonyms: Lamina basalis, Complexus basalis, Lamina vitra) - innermost layer of the choroid
== Blood supply ==
The choroid is supplied in humans by [[Ciliary arteries|posterior ciliary arteries]], originating form the [[ophtalmic artery]]. They are branching in a segmental distribution to the end arterioles and not [[anastomoses]]. This is clinically significant for diseases affecting choroidal blood supply. The [[macula]] responsible for central vision and the anterior part of the [[optic nerve]] are dependent on choroidal blood supply. <ref>Hayreh SS. Segmental nature of the choroidal vasculature. Br J Ophthalmol. 1975 Nov;59(11):631-48. PMID 812547 </ref>
==Mechanism==
[[Image:Calf-Eye-Posterior-With-Retina-Detached-2005-Oct-13.jpg|thumb|left|Calf's eye dissected to expose the choroid: its tapetum lucidum is iridescent blue]]
[[Melanin]], a darkly colored [[pigment]], helps the choroid limit uncontrolled reflection within the eye that would potentially result in the perception of confusing images. In humans and most other [[primates]], melanin occurs throughout the choroid. In [[albino]] humans, frequently melanin is absent and [[low vision|vision is low]]. In many animals, however, the partial absence of melanin contributes to superior [[night vision]]. In these animals, melanin is absent from a section of the choroid and within that section a layer of highly reflective tissue, the [[tapetum lucidum]], helps to collect light by reflecting it in a controlled manner. The uncontrolled reflection of light from dark choroid produces the photographic [[red-eye effect]] on photos, whereas the controlled reflection of light from the tapetum lucidum produces [[eyeshine]] (see [[Tapetum lucidum]]).
==See also==
*[[Chorioretinitis]]
*[[Uveitis]]
==Additional images==
<gallery>
Image:Gray878.png|Iris, front view.
Image:Gray880.png|The terminal portion of the optic nerve and its entrance into the eyeball, in horizontal section.
Image:Gray1206.png|The interior of the posterior half of the left eyeball.
</gallery>
== References ==
<references />
==External links==
* {{BUHistology|08008loa}}
{{Eye}}
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[[Category:Visual system]]
[[Category:Eye]]
[[bn:কোরয়েড]]
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[[es:Coroides]]
[[eu:Koroide]]
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[[he:שכבה דמית]]
[[lt:Gyslainė]]
[[nl:Vaatvlies]]
[[pl:Naczyniówka]]
[[sk:Cievovka]]
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