Microvascular Network and Its Endothelial Cells in the Human Iris

Purpose: The iris allows effective delivery of nutrients into the aqueous humor supplying the surrounded avascular tissues. However, possible underlying mechanisms of the iris vasculature have not been well established. This study aims to quantitatively assess the human iris vascular network, endothelial cell morphometries, and characterize endothelial junctions to better understand the properties of the iris vasculature. Materials and methods: The irises from human donor eyes were dissected and short fixed before float staining for VE-cadherin and claudin-5, f-actin and nuclei and flat-mounted for confocal imaging. The iris microvasculature was studied for its distribution and branch orders. The endothelial and nuclear morphometrics were measured for each vessel order. Characteristics of cellular junction staining and intracellular cytoskeleton were investigated. Results: The human iris vasculature was found to comprise of six orders of arteries, three orders of veins, and capillaries. The endothelial cell shape was long and narrow in all arteries, suggesting a high hemodynamic shear stress. Relatively large vessels ran radially in the superficial two-thirds of the iris, while smaller and denser vessels ran in the deepest third. Significant heterogeneity in vascular diameter, shape of the endothelia and nuclei, and the nuclear position was evident between artery, capillary and vein. Staining of junction proteins VE-cadherin and claudin-5 appeared non-uniform at the cell borders, especially in large veins. Conclusions: High rates of blood flow and special barrier properties are indicated by the morphological properties of the human iris vasculature. Detailed information of the iris vasculature combined with the inter- and intra-endothelial structure may help us further understand the physiological and pathogenic roles of the iris.