Reactions of efferent venous segments in the ciliary process vasculature of albino rabbits

In albino rabbits, the reactions of a defined venous segment of the ciliary process vasculature to vasoactive agents were studied using our new technique of in vivo microendoscopy and using supravital specimens of the anterior eye. This segment is situated in the pars plana of the ciliary body and is the continuation of the venules at the inner edge of the minor and major ciliary processes which posteriorly drain the blood in the veins of the peripheral choroid. Three- to 4 min after administration of carbachol, a constriction of this efferent venous segment was seen in the in vivo microendoscopy as well as in supravital specimens. The adjacent vessel segments remained relatively unchanged. Two- to 3 min after intra-arterial administration of atriopeptin (ANP), an intense constriction of the efferent venous segment, followed by a reactive hyperaemia, was found by in vivo microendoscopy. The iris veins which collect the blood from the iris and the iridial ciliary processes pass the pars plana without touching the ciliary process vasculature. No reactions to the vasoactive agents tested were observed in these vessels. It has been concluded that the efferent venous segment of the ciliary process may play a role in the regulation of perfusion pressure within the ciliary process capillaries.