Choroid 536484 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}} {{eye-stub}} [[Category:Visual system]] [[Category:Eye]] [[bn:কোরয়েড]] [[ca:Coroide]] [[de:Chorioidea]] [[el:Χοριοειδής χιτώνας]] [[es:Coroides]] [[eu:Koroide]] [[fr:Choroïde]] [[he:שכבה דמית]] [[lt:Gyslainė]] [[nl:Vaatvlies]] [[pl:Naczyniówka]] [[sk:Cievovka]] [[tr:Koroidea]]