Definition:

The choroid is the vascular layer of the eye that lies between the retina and the sclera. The choroid is thickest in the back of the eye at about 0.2 mm and narrows to 0.1 mm in the peripheral part of the eye. It contains the retinal pigmented epithelial cells and provides oxygen and nourishment to the outer retina. The choroid forms the uveal tract which includes the iris and the ciliary body.

Layers

The choroid is made of four different layers:

• Haller's layer (large blood vessel layer)
• Sattler's layer (medium-size blood vessels)
• Choriocapillaris (capillaries)
• Bruch's membrane (membrane on the innermost part of the choroid)

The dark-colored melanin pigment in the choroid absorbs light and limits reflections within the eye that could degrade vision. The melanin is also thought to protect the choroidal blood vessels against light toxicity. The choroidal pigment is what causes "red eyes" when flashed pictures are taken.

Diseases and Disorders of the Choroid

• Hemorrhagic choroidal detachment is a hemorrhage in the space above the choroid or in the choroid caused by the rupture of choroidal vessels. Although it can occur spontaneously, it is extremely rare. It usually occurs as a consequence of eye trauma during eye surgery. A hemorrhagic choroidal detachment can produce profound symptoms. Treatment consists of topical steroid eye drops,eye drops, and eye pressure-lowering eye drops. 
• Choroidal rupture is a complete break in the choroid, Bruch's membrane, and the retinal pigment epithelium that occurs as a result of blunt eye trauma such as getting hit with a fist. Unfortunately, many choroidal ruptures involve the center of the retina, called the macula. The macula allows us to have high quality, central vision. The injury leads to a loss of the photoreceptors in the macula and loss of central vision. If the rupture is not in the macula, central vision is retained.
• Choroidal nevi are a collection of pigmented or non-pigmented cells in the choroid, the vascular layer under the retina. Most choroidal nevi only need to be monitored. Your eye doctor will photograph the area of concern and check it frequently. Most do not need any treatment. If it has orange pigmentation, appears elevated, or has an unusual shape, it is possible that it could become a malignant choroidal melanoma. In this case, aggressive treatment is needed.
• Choroidal dystrophies are a group of inherited diseases that affect the choroid., Gyrate atrophy, Central areolar choroidal dystrophy, Diffuse choroidal atrophy, and Pigmented paravenous retinochoroidal atrophy are examples of choroidal dystrophies. Severe vision loss can occur in some of these dystrophies.
• Chorioretinitis is the most common disease that attacks the choroidea. This type of inflammation often produces floating dark spots and blurry vision. Young children and those people who are battling the Herpes Simplex Virus are usually affected by this disease. Antibiotics and corticosteroids are often used to successfully combat chorioretinitis.
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• Journal Manager Journal of Eye Diseases and Disorderss
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