Choroid - wikipedia Choroid Choroid Cross-section of human eye, with choroid labeled at top. Interior of anterior half of bulb of eye. ( Choroid labeled at right, second from the bottom. ) Details Artery short posterior ciliary arteries, long posterior ciliary arteries Identifiers Latin choroidea MeSH D002829 TA A15. 2.03. 002 FMA 58298 Anatomical terminology ( edit on Wikidata ) The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye, containing connective tissues, and lying between the retina and the sclera. The human choroid is thickest at the far extreme rear of the eye ( at 0.2 mm ), while in the outlying areas it narrows to 0.1 mm. The choroid provides oxygen and nourishment to the outer layers of the retina. Along with the ciliary body and iris, the choroid forms the uveal tract. The structure of the choroid is generally divided into four layers ( classified in order of furthest away from the retina to closest ) : 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 ; and Bruch 's membrane ( synonyms : Lamina basalis, Complexus basalis, Lamina vitra ) - innermost layer of the choroid. Contents 1 Blood supply 1.1 In bony fish 2 Mechanism 3 See also 4 Additional images 5 References 6 External links Blood supply There are two circulations of the eye : the retinal ( in the retina ) and uveal, supplied in humans by posterior ciliary arteries, originating from the ophthalmic artery. The arteries of the uveal circulation, supplying the uvea and outer and middle layers of the retina, are branches of the ophthalmic artery and enter the eyeball without passing with the optic nerve. The retinal circulation, on the other hand, derives its circulation from the central retinal artery, also a branch of the ophthalmic artery, but passing in conjunction with the optic nerve. 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. In bony fish Teleosts bear a body of capillary adjacent to the optic nerve called the choroidal gland. Though its function is not known, it is believed to be a supplemental oxygen carrier. Mechanism Melanin, a dark 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 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 Schematic cross section of the human eye ; choroid is shown in purple. Iris, front view The terminal portion of the optic nerve and its entrance into the eyeball, in horizontal section The interior of the posterior half of the left eyeball Structures of the eye labeled This image shows another labeled view of the structures of the eye Calf 's eye dissected to expose the choroid : its tapetum lucidum is iridescent blue References ^ Jump up to : MRCOphth Sacs questions Jump up ^ `` Sensory Reception : Human Vision : Structure and function of the Human Eye '' vol. 27, p. 174 Encyclopædia Britannica, 1987 Jump up ^ Hayreh S ( November 1975 ). `` Segmental nature of the choroidal vasculature ''. Br J Ophthalmol. 59 ( 11 ) : 631 -- 48. doi : 10.1136 / bjo. 59.11. 631. PMC 1017426. PMID 812547. Jump up ^ `` Eye ( Vertebrate ) '' McGraw - Hill Encyclopedia of Science and Technology, vol. 6, 2007. External links Histology image : 08008loa -- Histology Learning System at Boston University Anatomy of the globe of the human eye Fibrous tunic ( outer ) Sclera Episcleral layer Schlemm 's canal Trabecular meshwork Cornea Limbus layers Epithelium Bowman 's Stroma Dua 's layer Descemet 's Endothelium Uvea / vascular tunic ( middle ) Choroid Capillary lamina of choroid Bruch 's membrane Sattler 's layer Ciliary body Ciliary processes Ciliary muscle Pars plicata Pars plana Iris Stroma Pupil Iris dilator muscle Iris sphincter muscle Retina ( inner ) Layers Inner limiting membrane Nerve fiber layer Ganglion cell layer Inner plexiform layer Inner nuclear layer Outer plexiform layer Outer nuclear layer External limiting membrane Layer of rods and cones Retinal pigment epithelium Cells Photoreceptor cells ( Cone cell, Rod cell ) → ( Horizontal cell ) → Bipolar cell → ( Amacrine cell ) → Retina ganglion cell ( Midget cell, Parasol cell, Bistratified cell, Giant retina ganglion cells, Photosensitive ganglion cell ) → Diencephalon : P cell, M cell, K cell, Muller glia Other Macula Perifoveal area Parafoveal area Fovea Foveal avascular zone Foveola Optic disc Optic cup Ora serrata Anatomical regions of the eye Anterior segment Adnexa Fibrous tunic Anterior chamber Aqueous humour Iris Posterior chamber Ciliary body Lens Capsule of lens Zonule of Zinn Posterior segment Vitreous chamber Vitreous body Retina Choroid Other Keratocytes Ocular immune system Optical coherence tomography Eye care professional Eye disease Refractive error Accommodation Physiological Optics Visual perception Retrieved from `` https://en.wikipedia.org/w/index.php?title=Choroid&oldid=832027257 '' Categories : Human eye anatomy Visual system Hidden categories : Pages with unresolved properties Talk Contents About Wikipedia Bosanski Català Čeština Deutsch Eesti Ελληνικά Español Esperanto Euskara فارسی Français Gaeilge Galego 한국어 Hrvatski Ido Bahasa Indonesia Italiano עברית Lietuvių Nederlands Norsk Polski Português Română Русский Slovenčina Српски / srpski Srpskohrvatski / српскохрватски Татарча / tatarça Türkçe Українська 中文 25 more Edit links This page was last edited on 23 March 2018, at 11 : 33 ( UTC ). 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Question: what is the function of the choroid layer
Answer: provides oxygen and nourishment to the outer layers of the retina