The Normal Eye - Choroid
At the region of the ora serata, the ciliary body gives way to the choroid, which is a pigmented vascular undercoat between the sclera and the retina. The principle function of the choroid is through its blood supply to nourish the outer retina and to provide a pathway for the vessels that nourish the anterior chamber.
To this end, the choroid has an extremely rich vasculature, which is fed by short choroidal arteries that cluster into the eye around the optic nerve. The choroid inner surface, known as the choriocapillaris, has as its primary function the nourishment of the retina. However, this network also has an important function in maintenance of intra- ocular pressure.
The choriocapillaris is separated from the retinal pigment epithelium by a thick basal lamina known as Bruch's membrane. As the retina and choroid age, Bruch's membrane undergoes a series of changes including an increased thickness and stratification. An amorphous granular material known as drusen is deposited beneath the retinal pigment epithelium with ageing. Drusen is now thought to play a causal role in a progressive condition known as Age- Related Macular Degeneration.