Visual Anatomy 視覚解剖学

　脈絡膜（みゃくらくまく、英：choroid ）

　The choroid, also known as the choroidea or choroid coat, is a part of the uvea, the vascular layer of the eye, and contains connective tissues, and lies 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.

【語句】

・uvea：眼球血管膜・vascular：脈管の・connective tissue：結合組織・retina：網膜・sclera：強膜・outlying：中心を離れた nourishment：栄養・ciliary body：毛様体・iris：虹彩・uveal tract：ブドウ膜・capillary：毛細血管・Lamina basalis：基板

【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 (a branch of the internal carotid 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 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. 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.

　Choroidal blood flow revealed with ICG-angiography (Spectralis, Heidelberg) and laser Doppler imaging

【語句】

・posterior ciliary artery：後毛様体動脈・ophthalmic artery：眼動脈・internal carotid artery：内頚動脈・optic nerve：視神経・central retinal artery：網膜中心動脈・distribution：分布・arteriole：小動脈・anastomose：吻合する・significant：重要な、意味のある・macula：網膜黄斑・optical coherence tomography：光干渉断層撮影・Indocyanine green angiography：インドシアニングリーン蛍光眼底撮影法・laser Doppler imaging：レーザードップラー画像？

【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).