Background or non proliferative diabetic retinopathy will advance to proliferative diabetic retinopathy when new abnormal blood vessels begin to grow due to poor profusion of blood (ischemia) to parts of the retina. The capillary bed that lies between the retinal arteries and veins are blocked leaving the retina under-nourished. The body tries to compensate for this with new vessel growth, but these vessels are fragile abnormal and leak. If left alone, they can organize and form fibrous bands which can contract and pull on the retina causing further damage in the form of retinal and vitreous hemorrhages and retinal traction detachments. Your doctor will perform laser surgery to shrink and discourage the growth of these abnormal vessels.