 The origin seems to be related to a continuous differentiation throughout the growth of the tissue and even further differentiation during adulthood.After excision the choroid collapses partially, histologic preparations also alter the local pressure and fluid content of different sections in the tissue, thus requiring preparations with rubber solution or others that can conserve the vascular status of living tissue.Novel diagnostic methods, especially optical coherence tomography have widened the understanding of the real time, in vivo status of the different layers.