ARTERIOVENOUS ANASTOMOSES OF THE EPISCLERAL VASCULATURE IN THE RABBITAND RAT EYE

Purpose: To obtain more information about the functional significance of arteriovenous anastomoses as regulatory elements, the authors inves tigated the topography and innervation of episcleral anastomoses in th e rat and rabbit. Materials and Methods: The topography of arterioveno us anastomoses in the limbal and episcleral vasculature of the rat and rabbit eye was studied by scanning electron microscopy of vascular re sin casts. The perivascular distribution of the following neuropeptide s was investigated by fluorescence immunohistochemistry: neuropeptide Y (NPY). vasoactive intestinal polypeptide (VIP), substance P (SP), an d calcitonin gene-related peptide (CGRP). Results: The episcleral arte riovenous anastomoses connect arterioles directly with the episcleral venous plexus which also drains the aqueous humor. The nerve fiber ple xus around the episcleral arteriovenous anastomoses is far mon dense t han around arteriovenous connections at the limbal arcades. NPY-, VIP- , SP-, and CGRP-immunoactive fibers concentrate at the arteriolar segm ent of the episcleral arteriovenous anastomoses and are reduced at the venular segment. Still, numerous VIP-IR fibers are on the venous side of the rabbit episcleral anastomoses. Conclusion: We conclude that th e elaborated innervation of the episcleral anastomoses is a prerequisi te for a subtle modulation of the blood flow and possibly of the aqueo us humor outflow dynamics.