The
choroid, also known as the
choroidea or
choroid coat, is the
vascular layer of the
eye, containing
connective tissue, and lying between the
retina and the
sclera. The human choroid is thickest at the far extreme rear of the eye (at 0.2 mm), while in the outlying areas it narrows to 0.1 mm. The choroid provides
oxygen and nourishment to the outer layers of the
retina. Along with the
ciliary body and
iris, the choroid forms the
uveal tract. The structure of the choroid is generally divided into four layers (classified in order of furthest away from the retina to closest):
- Haller's layer - outermost layer of the choroid consisting of larger diameter blood vessels;
- Sattler's layer - layer of medium diameter blood vessels;
- Choriocapillaris - layer of capillaries; and
- Bruch's membrane (synonyms: Lamina basalis, Complexus basalis, Lamina vitra) - innermost layer of the choroid.