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. Also, all of the normal structures can be affected by genetic mistakes causing slow degeneration over time.