choroids


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choroids 

The highly vascular tunic of the eye lying between the retina and sclera. Its main function is to nourish the retina (oxygen and nutrients) and remove waste products. It is a thin membrane extending from the optic nerve to the ora serrata. It contains blood vessels, capillaries, nerves, collagen and melanocytes, as well as fibroblasts, macrophages, mast cells and plasma cells. It consists of five main layers from without inward: the suprachoroid (lamina fusca), the layers of vessels (Haller's layer and Sattler's layer), the choriocapillaris and the membrane of Bruch (lamina vitrea). The blood supply is provided mostly by the short posterior ciliary arteries and to a lesser extent by the long posterior ciliary arteries, as well as some branches from anterior ciliary arteries. Venous blood drains into the vortex veins. The posterior choroid is thickest in hyperopia and thinnest in myopia. Note: some authors consider the suprachoroid as belonging to the sclera. However, when choroid and sclera are separated, part of the suprachoroid adheres to the choroid and part to the sclera. See choroiditis; epichoroid; choroidal naevus; choroidal neovascularization; suprachoroidal space.
References in periodicals archive ?
Choroid plexus carcinoma: case report and review of literatura.
Melanotic choroid plexus carcinoma of the posteior fossa.
The choroid in the SDT rats was significantly thicker than in the normal SD rats in this experiment.
Around the entrance of the optic nerve they penetrate the sclera and reach the choroid as the short posterior ciliary arteries [11].
Interestingly, in half of the cases, the aqueous humour covers mainly the temporal part of the optic disc and the adjacent choroid on the same side.
Choroidal dysfunction theory states that it is the choroid that is the major site for the development of CSCR.
Recent evidence from the chick model suggests that the retina is the major site of action of atropine and that atropine likely exerts its action via intermediaries such as nitric oxide (NO) and dopamine [10] although there is also evidence that it may act directly on the choroid [11].
In different experimental animal models, the choroid has been shown to be associated with the development of the refractive state and axial elongation.
HAS2 gene expression of the choroid in form-deprived chick eyes was not significantly different from controls, but increased significantly during recovery period [25].
The choroid plays a significant part in the physiological function and pathogenesis of eyes: the blood flow per unit weight of choroid is higher than that of any other tissue and choroid acts as the vascular supply for the optic nerve, retinal pigment, outer retina, epithelium, and avascular fovea.
Generally, modern medicine has confirmed that retinitis pigmentosa sets on with the degeneration of photoreceptors and is then involved with RPE and the choroid in the progression of cell death.
However, the choroid is a three-dimensional structure with considerable topographic variation.