Fig. 1: Compartments created in the CellDesigner platform in line with the structure and function of the outer retina.

The outer retina lies internal to a layer of fenestrated choroidal capillaries called the choriocapillaris that supply the retina with oxygen, lipoproteins, glucose, vitamins and other nutrients, as well as removing waste substances such as carbon dioxide and lactate. The connective tissue layer between the choriocapillaris and the RPE is the Bruch’s Membrane. It is made up of five layers containing ECM proteins and acts rather like a sieve, providing a degree of constraint to the reciprocal exchange of molecules, nutrients, fluids, and waste products between the retina and circulation. The RPE is made up of a single layer of hexagonal cells and serves many functions. With tight junctions between the lateral surfaces, the RPE functions as part of the blood-ocular barrier, isolating the inner eye from systemic influences. Separating the inner eye from circulation provides immune privilege protecting the vital cells and structures from potential damage or loss of function via inflammatory immune response. The RPE is responsible for the selective transport and processing of all nutrients, metabolites, signaling molecules, and waste products to and from the inner retina, including the photoreceptors. Note that compartments are not drawn to scale.