Endothelial dysfunction is a key pathogenic mechanism of CVD. The retinal microvascular network offers a unique, non-invasive window to study endothelial function. Recently, dynamic measurement of retinal vessel caliber using flicker light stimulation has been used to evaluate potential endothelial dysfunction and other mechanisms in CVD. A variety of studies now indicate that retinal vasodilation during flicker light simulation is reduced in diabetes, hypertension, hyperlipidemia and obesity, and may be influenced by age and race/ethnicity. These data suggest that flicker light-induced retinal vasodilation may be a unique and non-invasive measure of endothelial dysfunction. This review focuses recent studies on systemic associations of flicker light-induced retinal vasodilation, and discusses the potential for future research in this area.