Choroid(redirected from choroidal)
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the connective-tissue coat of the eye located between the retina and the sciera. It is through the choroid that metabolites and oxygen pass from the blood to the pigmentary epithelium and photoreceptors of the retina.
The choroid includes a suprachoroid layer facing the sciera, a layer of large veins, a layer of arteries and veins, the choriocapil-laris, and Bruch’s membrane. The suprachoroid layer consists of compact reticulin and collagenous fibers. It is rich in fibroblasts and melanocytes, whose processes run through the entire choroid. The arteries and veins of the choroid have a double endothelial lining and basal and adventitial layers. Bruch’s membrane is made up of an amorphous substance containing elastic reticulin and collagenous fibers. It is bounded on the inside by a cell membrane of pigmentary epithelium and on the outside by a porous membrane of capillary endothelium.
The choroid of some fishes and mammals, for example, ungulates, has a reflecting layer, or a mirror, that intensifies the light stimulation of the photoreceptors and increases the sensitivity of the eye to light.
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O. G. STROEVA