Purpose: To quantitatively investigate the distribution of blood vessels in different neural layers of the human retina. Methods: 16 human donor eyes were perfusion-fixed and labelled for endothelial f-actin. Retinal eccentricity located 3mm superior to the optic disk was studied using confocal scanning laser microscopy. Immunohistochemical methods applied to whole-mount and transverse sections were used to co-localise capillary networks with neuronal elements. Capillary morphometry, diameter

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... d density measurements were compared between networks. Results : Four different capillary networks were identified and quantified in the following regions: (1) Nerve fibre layer (NFL). (2) Retinal ganglion cell (RGC) layer. (3) Border of inner plexiform layer (IPL) and superficial boundary of the inner nuclear layer (INL). (4) Boundary of deep INL and outer plexiform layer. The inner most and outermost capillary networks demonstrated a laminar configuration while IPL and deep INL networks displayed a complex three-dimensional configuration. Capillary diameter in RGC and IPL networks were significantly less than other networks. Capillary density was greatest in the RGC network (26.74%) and was significantly greater than the NFL (13.69%), IPL (11.28%) and deep INL (16.12%) networks. Conclusions: The unique metabolic demands of neuronal sub-compartments may influence the morphometric features of regional capillary networks. Differences in capillary diameter and density between networks may have important correlations with neuronal function in the human retina. These findings may be important for understanding pathogenic mechanisms in retinal vascular disease.