The choroid is a layer at the back of the eye situated between the retina and sclera. It consists mainly of connective tissues and blood vessels, which provide oxygen and nourishment to the retinal cells.

The back of the eye is made up of three layers, with the retina being the innermost layer and the sclera is the most external (white of the eye). The choroid is situated in between these two layers.
Side view of the eye showing the location of the retina, choroid and sclera