Retinal blood vessels have been suggested to be an index of the cerebral and coronary microvasculature function. Since the retinal vessels are not under direct sympathetic control, this vascular bed is an ideal location to examine local mechanisms of vascular regulation(i.e. metabolite/endothelial and myogenic). Based on previously published data on animal and human responses, the central purpose for the proposed research is to compare the retinal and brachial vasodilatation responses in healthy subjects using the Dynamic Vessel Analyzer (DVA). Our rationale for this proposal is to better understand retinal blood flow in healthy individuals, gain insight into vascular reactivity in different vascular beds, and lastly to establish standards and reproducibility of DVA Measurements.