Choroid

Choroid
Choroid
Schematic diagram of the human eye en.svg
Schematic cross section of the human eye; choroid is shown in purple.
Gray875.png
Interior of anterior half of bulb of eye. (Choroid labeled at right, second from the bottom.)
Latin choroidea
Gray's subject #225 1009
Artery short posterior ciliary arteries, long posterior ciliary arteries
MeSH Choroid

The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye, containing connective tissue, 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.[1] 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:

  • Haller's layer - outermost layer of the choroid consisting of larger diameter blood vessels;[1]
  • Sattler's layer - layer of medium diameter blood vessels;[1]
  • Choriocapillaris - layer of capillaries;[1] and
  • Bruch's membrane (synonyms: Lamina basalis, Complexus basalis, Lamina vitra) - innermost layer of the choroid.[1]

Contents

Blood supply

There are two hundred circulations of the eye: the retinal 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.[2] 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.[3]

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.[4]

Mechanism

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 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

Additional images

References

  1. ^ a b c d e MRCOphth Sacs questions
  2. ^ "Sensory Reception: Human Vision: Structure and function of the Human Eye" vol. 27, p. 174 Encyclopaedia Britannica, 1987
  3. ^ Hayreh SS. (Nov 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. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1017426. 
  4. ^ "Eye (Vertebrate)" McGraw-Hill Encyclopedia of Science and Technology, vol. 6, 2007.

External links


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См. также в других словарях:

  • Choroid — Cho roid, a. [gr. ?; ? chorion + e i^dos form.] (Anat.) resembling the chorion; as, the choroid plexuses of the ventricles of the brain, and the choroid coat of the eyeball. n. The choroid coat of the eye. See {Eye}. [1913 Webster] {Choroid… …   The Collaborative International Dictionary of English

  • choroid — 1680s, from Latinized form of Gk. khoroeides, a corruption of khorioeides, from khorion (see CHORION (Cf. chorion)) + eidos resemblance (see OID (Cf. oid)) …   Etymology dictionary

  • choroid — [kôr′oid΄] adj. [Gr choroeidēs, contr. < chorioeidēs < chorion, CHORION + eidēs, OID] designating or of the chorion or certain other vascular membranes n. the dark, vascular membrane that forms the middle coat of the eye, between the sclera …   English World dictionary

  • choroid — The middle vascular tunic of the eye lying between the pigment epithelium and the sclera. SYN: choroidea [TA]. [G. choroeides, a false reading for chorioeides, like a membrane] * * * cho·roid kō(ə)r .ȯid, kȯ(ə)r also cho·ri·oid kōr ē .ȯid,… …   Medical dictionary

  • choroid — UK [ˈkɔːrɔɪd] / US [ˈkɔrɔɪd] noun [countable] Word forms choroid : singular choroid plural choroids medical the part of your eye that is between the retina and the white of your eye. The coloured iris at the front of your eye is part of the… …   English dictionary

  • choroid — also chorioid noun Etymology: New Latin choroides resembling the chorion, from Greek chorioeidēs, from chorion chorion Date: 1683 a vascular membrane containing large branched pigmented cells that lies between the retina and the sclera of the… …   New Collegiate Dictionary

  • choroid — Middle layer of the vertebrate eye, between retina and sclera. Well vascularized and also pigmented to throw light back onto the retina (the tapetum is an irridescent layer in the choroid of some eyes). Not to be confused with the choroid plexus …   Dictionary of molecular biology

  • choroid — /kawr oyd, kohr /, Anat. adj. 1. like the chorion; membranous. n. 2. See choroid coat. Also, choroidal, chorioid, chorioidal. [1625 35; < Gk choroeidés false reading for chorioeidés CHORIOID] * * * …   Universalium

  • choroid — noun /ˈkəʊrɔɪd,ˈkoʊrɔɪd/ The vascular layer of the eye lying between the retina and the sclera. See Also: chorioid, choroidea, choroid coat …   Wiktionary

  • choroid(o)- — a combining form denoting relationship to the choroid …   Medical dictionary


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