The vessel architecture of the pars plana in the cynomolgus monkey, rat and rabbit eye. A scanning electron microscopic study of plastic corrosion casts.

In the cynomolgus monkey, rabbit and rat the architecture of the pars plana vasculature was investigated using scanning electron micrographs of resin casts. The most complex vessel architecture was found in the cynomolgus monkey. Here, the pars plana venules have affluxes from the ciliary processes, ciliary muscle and iris. Numerous interconnections between these venules exist in the central portion of the pars plana. Arterial affluxes reach the pars plana not until the choriocapillaries. The variations of this architecture in the rat and rabbit are not only caused by the different size of the ciliary muscle and its vascularization. In the rat the most peripheral part of the uveal supply of the retina represents a transition form between pars plana venules and the choriocapillaries. In the rabbit, two vascular layers exist in the pars plana while in the cynomolgus monkey and rat the pars plana vessels spread out in one plane. The functional significance of the vessel architecture and the species differences are discussed.