Participants with a range of severity of diabetic retinopathy and healthy volunteers will be evaluated once for serum levels of cell adhesion molecules, chemokines and vascular endothelial growth factor. This study may lead to a better understanding of the pathogenesis of diabetic retinopathy and the identifying of possible targets for treatment. All study participants will undergo an ocular exam and ophthalmic photography. Blood is drawn for the analysis of these serum factors.