Fig. 4.

Structure of the human macula. (A) Brightfield image of the extrafoveal macula; in normal eyes, the neural retina, RPE and choroid exist as an interdependent unit. Light enters the retina from the top of the panel, penetrates the inner retina and excites photoreceptor cell outer segments (OS). Stray photons are absorbed by melanosomes in the RPE and choroidal melanocytes (m). The phototransduction cascade results in arrest of glutamate release from photoreceptor cells and the excitation of neurons in the inner nuclear layer (INL), which in turn excite the ganglion cells (GC) that elaborate axons to the brain. The choroid itself is divided into the choriocapillaris (CC), Sattler's layer (SL), Haller's layer (HL), and the suprachoroidea, adjacent to the sclera (SC). Whereas the choriocapillaris is the vascular supply for the photoreceptor cells and RPE, the inner retina has its own vascular network (retinal capillaries, RC). B, same field as A shown with UEA-I (red), anti-CD45 antibody (green) and the nuclear stain DAPI (blue). Note the labeling of retinal and choroidal endothelial cells. The intense fluorescence at the level of the RPE is due to lipofuscin autofluorescence. C, flat section through the choriocapillaris layer shows dense, anastomosing network of large caliber capillaries (UEA-I, red); D, deeper section through the outer choroid. Scalebar, 50 μm.