Underneath the pigment layer is a layer of blood vessels called the choroid. The choroid keeps the photoreceptors alive by allowing nutrients to diffuse to them. Finally the eyeball itself is made of a tough white collagen tissue called the sclera. The sclera maintains an optimal shape of the eye and protects the sensitive internal tissues from damage. This is a schematic cross-section of the retina and underlying tissues.
Light passes from top to bottom, through the retina to the rods and cones.
The retinal pigment epithelium rests on Bruch's membrane, under which is the choriocapillaris. All these structures are intimately related in the normal eye but are subject to numerous disease processes. Commonly, fluid or blood can collect within or between layers causing dysfunction. Abnormal cells can grow into the layers. Even new blood vessels can appear either under the rods and cones or under the retinal pigment epithelium.