Angioarchitecture and innervation of the primate anterior episclera.
OBJECTIVE
To investigate the primate episcleral vasculature and its innervation with respect to morphological specializations.


METHODS
Serial sections of the anterior episclera of 8 monkey eyes and 20 human eyes were investigated enzyme- and immunohistochemically using antibodies against smooth-muscle alpha-actin (SMA), neurofilament, synaptophysin, substance P (SP), calcitonin gene-related peptide (CGRP), vesicular acetylcholine transporter (VACHT), vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), tyrosine hydroxylase (TH), vesicular monoamine transporter II (VMAT II), as well as the NADPH-diaphorase reaction. Arteriovenous anastomoses (AVA) were quantified.


RESULTS
All episcleral vessels including veins showed intense staining for SMA. Capillary loops were only seen in the limbal arcades, not in the episclera itself. Instead, AVA connected the episcleral arteries with the veins, which formed an interlacing vascular network. In the monkey episclera, 4-6/mm2 AVA were found; in the human episclera, 0.5-1/mm2. Numerous nerve endings staining for NADPHd (NADPHdiaphorase) and TH surrounded all episcleral vessels including anastomoses and veins. NPY, VIP, and VACHT-immunoreactive (IR) nerve terminals were less numerous. CGRP and SP-IR terminals were seen both at the vessels and in the intervascular connective tissue.


CONCLUSIONS
The episcleral vasculature shows a specialized morphology with absence of capillaries, numerous arteriovenous anastomoses, a muscle-rich venous network, and intense innervation by vasodilative and vasoconstrictive nerves. This might allow regulation of blood flow and volume in the episcleral vessels and Voigt's capillaries for thermoregulation and modulation of episcleral venous pressure and thereby outflow facility.
Selbach
J Michael
JM
Department of Anatomy II, University of Erlangen-Nürnberg, Erlangen, Germany. michael.selbach@arcor.de
Rohen
Johannes W
JW
Steuhl
Klaus-Peter
KP
Lütjen-Drecoll
Elke
E
D000199:Actins / Q000378:metabolism; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D000869:Anterior Eye Segment / Q000098:blood supply* / Q000294:innervation*; D001163:Arteriovenous Anastomosis / Q000033:anatomy & histology / Q000378:metabolism; D015415:Biomarkers / Q000378:metabolism; D019842:Ciliary Arteries / Q000033:anatomy & histology* / Q000294:innervation; D004730:Endothelium, Vascular / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D008252:Macaca fascicularis; D008875:Middle Aged; D009131:Muscle, Smooth, Vascular / Q000033:anatomy & histology / Q000378:metabolism; D009252:NADPH Dehydrogenase / Q000378:metabolism; D009412:Nerve Fibers; D009419:Nerve Tissue Proteins / Q000378:metabolism; D017933:Peripheral Nervous System / Q000033:anatomy & histology* / Q000378:metabolism; D012590:Sclera / Q000098:blood supply* / Q000294:innervation*
D000199:Actins; D015415:Biomarkers; D009419:Nerve Tissue Proteins; D009252:NADPH Dehydrogenase