Quantitative assessment of the human retinal microvasculature with or without vascular comorbidity.

PURPOSE: To determine whether morbidity and mortality in patients with cardiovascular comorbidities, but no known ocular disease, is related to demonstrable quantitative changes in the retinal microvasculature. METHODS: Eleven eyes from 8 donors with cardiovascular comorbidities as a diseased group were compared with 16 eyes from 14 donors free from vascular disease as a control group. All eyes had no known ocular disease. The retina was perfusion-fixed and labeled for endothelial f-actin using micro-cannulation techniques. The retinal microvasculature 3 mm superior to the optic disc was imaged with confocal scanning laser microscopy. Quantitative measurements of capillary diameter and density were obtained using two-dimensional image reconstructions. Pathological vascular changes in other regions of the retinal vasculature found in the diseased group were identified and reconstructed in two or three dimensions. RESULTS: Capillary densities were significantly different between each capillary network in the diseased group. There was a significant decrease in density between both the nerve fiber layer and retinal ganglion cell layer of the diseased group when compared with those layers in the control eyes. There were pathological vascular changes including microaneurysms and tortuous, dilated venules identified in the diseased group. CONCLUSIONS: Cardiovascular comorbidities may be associated with changes to the capillary density within the human retinal microvasculature, before the manifestation of known ocular diseases. These differences in capillary density may have important correlations with neuronal function and facilitates the basis of understanding pathogenic mechanisms in retinal vascular disease.

Phenotypic heterogeneity in the endothelium of the human vortex vein system.

The vortex vein system is the drainage pathway for the choroidal circulation and serves an important function in the effective drainage of the exceptionally high blood flow from the choroidal circulation. As there are only 4-6 vortex veins, a large volume of blood must be drained from many choroidal veins into each individual vortex vein. The vortex vein system must also cope with passing through tissues of different rigidity and significant pressure gradient as it transverses from the intrao-cular to the extra-ocular compartments. However, little is known about how the vortex vein system works under such complex situations in both physiological and pathological condition. Endothelial cells play a vital role in other vascular systems, but they have not been studied in detail in the vortex vein system. The purpose of this study is to characterise the intracellular structures and morphology in both the intra-and extra-ocular regions of the human vortex vein system. We hypothesise the presence of endothelial phenotypic heterogeneity through the vortex vein system. The inferior temporal vortex vein system from human donor eyes were obtained and studied histologically using confocal microscopy. The f-actin cytoskeleton and nuclei were labelled using Alexa Fluor conjugated Phalloidin and YO-PRO-1. Eight regions of the vortex vein system were examined with the venous endothelium studied in detail with quantitative data obtained for endothelial cell and nuclei size and shape. Significant endothelial phenotypic heterogeneity was found throughout the vortex vein system with the most obvious differences observed between the ampulla and its downstream regions. Variation in the distribution pattern of smooth muscle cells, in particular the absence of smooth muscle cells around the ampulla, was noted. Our results suggest the presence of significantly different haemodynamic forces in different regions of the vortex vein system and indicate that the vortex vein system may play important roles in regulation of the choroidal circulation.

Age-related changes in venous endothelial phenotype at human retinal artery-vein crossing points.

PURPOSE: To investigate the venous endothelial phenotype at retinal artery-vein (AV) crossings and age-related changes in human cadaveric eyes. METHODS: Eighteen human donor eyes free of known ocular diseases were divided into two groups according to age (≤30 and >50 years). The central retinal artery was cannulated and perfused with oxygenated Ringer's solution with 1% bovine serum albumin. The perfusate solutions were switched to fixative, membrane permeabilizing solution, and selected labeling solutions for microfilament F-actin and nucleic acid in vascular endothelial cells and smooth muscle cells. The eyes were then immersion fixed and the retinas flat mounted. The venous endothelial cells were examined by confocal microscopy at the AV, pre-AV, and post-AV crossing regions. RESULTS: There was no significant difference between the younger and older groups in endothelial cell length upstream or downstream from an AV crossing. At the AV crossing, the venous endothelial cells were shorter in the younger group and longer in the older group compared with those upstream or downstream from the AV crossing. Stress fibers were not frequently observed in the endothelial cells of younger donors. However, the older group had numerous stress fibers in their endothelia at AV crossing points. CONCLUSIONS: Age-related phenotype changes in venous endothelial cells have been identified in the region of AV crossings providing supportive evidence for the hypothesis of age-related and site-specific changes in the vascular endothelial cells as an important factor contributing to the pathogenesis of branch retinal vein occlusion.