choroid

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 (a branch of the internal carotid artery).[https://www.ncbi.nlm.nih.gov/books/NBK53329/ The Ocular Circulation] 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."Sensory Reception: Human Vision: Structure and function of the Human Eye" vol. 27, p. 174 Encyclopædia Britannica, 1987 They branch in a segmental distribution to 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.{{cite journal | doi = 10.1136/bjo.59.11.631 | last1 = Hayreh | first1 = SS. |name-list-style=vanc |date=November 1975 | title = Segmental nature of the choroidal vasculature | journal = Br J Ophthalmol | volume = 59 | issue = 11| pages = 631–648 | pmid = 812547 | pmc = 1017426 }} The structure of choroidal vessels can be revealed by optical coherence tomography, and blood flow can be revealed by Indocyanine green angiography, and laser Doppler imaging.Puyo, Léo, Michel Paques, Mathias Fink, José-Alain Sahel, and Michael Atlan. "Choroidal vasculature imaging with laser Doppler holography." Biomedical optics express 10, no. 2 (2019): 995–1012.

File:LDHvsICG.jpgLéo Puyo, Michel Paques, and Michael Atlan, "Spatio-temporal filtering in laser Doppler holography for retinal blood flow imaging," Biomed. Opt. Express 11, 3274–3287 (2020)]]

Teleosts bear a body of capillaries adjacent to the optic nerve called the choroidal gland. Though its function is not known, it is believed to be a supplemental oxygen carrier."Eye (Vertebrate)" McGraw-Hill Encyclopedia of Science and Technology, vol. 6, 2007.

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).

The choroid was first described by Democritus (c. 460 – c. 370 BCE) around 400 BCE, calling it the "chitoon

malista somphos" (more spongy tunic [than the sclera]).Dolz-Marco, R., Gallego-Pinazo, R., Dansingani, K. K., & Yannuzzi, L. A. (2017). The history of the choroid. In J. Chhablani & J. Ruiz-Medrano (Eds.), Choroidal Disorders (Vol. 1–5, pp. 1–5). Academic Press. {{doi|10.1016/b978-0-12-805313-3.00001-6}} Democritus likely saw the choroid from dissections of animal eyes.{{Cite journal |last=Rudolph |first=Kelli |date= 2012|title=Democritus' Ophthalmology |url=https://www.cambridge.org/core/journals/classical-quarterly/article/abs/democritus-ophthalmology/75F141868614774250E11F39DB7C5072 |journal=The Classical Quarterly |language=en |volume=62 |issue=2 |pages=496–501 |doi=10.1017/S0009838812000109 |issn=0009-8388}}

About 100 years later, Herophilos (c. 335 – 280 BCE) also described the choroid from his dissections on eyes of cadavers.{{Cite book |last=Staden |first=Heinrich von |url=https://books.google.com/books?id=rGhlIfJZkVoC |title=Herophilus: The Art of Medicine in Early Alexandria: Edition, Translation and Essays |date=1989 |publisher=Cambridge University Press |isbn=978-0-521-23646-1 |language=en}}Reverón, R. (2015). Herophilos, the great anatomist of antiquity. Anatomy, 9(2), 108–111. {{doi|10.2399/ana.15.003}} https://dergipark.org.tr/en/download/article-file/371071

Choroid is the most common site for metastasis in the eye due to its extensive vascular supply. The origin of the metastases are usually from breast cancer, lung cancer, gastrointestinal cancer, and kidney cancer. Bilateral choroidal metastases are usually due to breast cancer, while unilateral metastasis is due to lung cancer. Choroidal metastases should be differentiated from uveal melanoma, where the latter is a primary tumour arising from the choroid itself.{{cite journal |vauthors=Arepalli S, Kaliki S, Shields CL |title=Choroidal metastases: origin, features, and therapy |journal=Indian Journal of Ophthalmology |volume=63 |issue=2 |pages=122–127 |date=February 2015 |pmid=25827542 |pmc=4399120 |doi=10.4103/0301-4738.154380 |url= |doi-access=free }}

• Chorioretinitis
• Uveitis

Schematic diagram of the human eye en.svg|Schematic cross section of the human eye; choroid is shown in purple.

File:Laser_Doppler_holography_of_retinal_and_choroidal_blood_flow.jpg|Laser Doppler imaging of retinal and choroidal blood flow

File:Gray878.png|Iris, front view

File:Gray880.png|The terminal portion of the optic nerve and its entrance into the eyeball, in horizontal section

File:Gray1206.png|The interior of the posterior half of the left eyeball

File:Three Main Layers of the Eye.png|Structures of the eye labeled

File:Three Internal chambers of the Eye.svg|This image shows another labeled view of the structures of the eye

File:Calf-Eye-Posterior-With-Retina-Detached-2005-Oct-13.jpg|Calf's eye dissected to expose the choroid: its tapetum lucidum is iridescent blue

{{Reflist}}

• {{BUHistology|08008loa}}

{{Eye}}

{{Authority control}}

Category:Human eye anatomy

Category:Visual system