Choroid
Schematic cross section of the human eye; choroid is shown in purple.
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
Dorlands/Elsevier	c_32/12237606

The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye lying between the retina and the sclera, with a thickness about 0.5 mm. The choroid provides oxygen and nourishment to the outer layers of the retina [1].

Along with the ciliary body and iris, the choroid forms the uveal tract. In humans and other primates, darkly colored melanin pigment in the choroid helps limit reflections within the eye that would potentially result in the perception of confusing images. Poor vision frequently results from lack of this pigmentation in human albinos. By contrast, the choroid of many other animals contains reflective materials that help to collect light in dim situations; this is one type of tapetum lucidum.

The red eye effect on photos is caused by the reflection of light from choroid. It appears red because of the choroid's blood vessels.

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 - innermost layer of the choroid

Blood supply

The choroid is supplied in humans by posterior ciliary arteries 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 dependant on choroidal blood supply. ^[1]

See also

• Chorioretinitis
• Uveitis

Additional images

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.

References

1. ^ Hayreh SS. Segmental nature of the choroidal vasculature. Br J Ophthalmol. 1975 Nov;59(11):631-48. PMID 812547

External links

• Histology at BU 08008loa

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