Coroideos

Coroideos are the choroidal tissues of the eye, a vascular layer forming the posterior part of the uveal tract, lying between the retina and the sclera. The choroid is supplied by the posterior ciliary arteries and drained by choroidal veins, and it is segmented into three vascular strata: the choriocapillaris, the network of small capillaries closest to the retina; Sattler's layer, consisting of medium-sized vessels; and Haller's layer, containing larger vessels. The tissue also contains melanocytes that provide pigment, helping to absorb stray light and reduce reflection.

The main function of the coroides is to provide oxygen and nutrients to the outer retina, including photoreceptors, and to remove metabolic waste. It also helps regulate thermal exchange and light transmission to the retina, via its pigment and vascular network; a healthy choroid contributes to ocular immune defense through resident macrophages.

Clinical relevance: Diseases affecting the choroid include inflammation (choroiditis), choroidal neovascularization as seen in age-related macular degeneration, choroidal tumors, and detachments or effusions. Choroidal thickness can be altered in high myopia or inflammatory conditions, and imaging modalities such as optical coherence tomography and enhanced depth imaging help assess the choroid.