Microvascular pattern of the retina in the Japanese monkey (Macaca fuscata fuscata).

The microvascular architecture of the retina in the Japanese monkey was revealed using scanning electron microscopy of microvascular corrosion casts. At the optic nerve disc, the central retinal artery radiated to four primary retinal arterioles: the superior and inferior temporal arterioles and superior and inferior nasal arterioles. A dense retinal capillary network showed regional differences in density. The capillary networks observed were divided in four parts: the optic nerve disc, macula, equator, and ora serrata. At the optic nerve disc, the network was a multi-laminar structure containing the radial peripapillary capillaries in parallel with the nerve fibers at the innermost layer. At the macula, the retinal capillaries formed a ring around the central fovea which is an avascular area. At the equatorial part, the network was observed to be double-layered: a superficial capillary network located in the nerve fiber layer and a deep capillary network located at the external nuclear lamina. The former showed a 30-50 microns wide capillary-free zone (CFZ) around arterioles. The latter was undulated in smaller capillaries without the CFZ. At the ora serrata, the network changed to a single layer with coarse ovoid meshes, and the CFZ developed to 50-70 microns in width around arterioles. Hence, the microvasculature of the retina in the Japanese monkey showed regional variations correlating with the fine structure of the retinal layers, e.g., the multi-laminar capillary network for the thick nerve fiber layer at the optic nerve disc part, and the central avascular fovea for the absence of any structure inside the external nuclear lamina. Capillary-free zone occurred since the retinal capillaries were located in the same level as the arterioles.