Over time, NPDR may progress to more severe PDR, the hallmark of which is neovascularization on the surface of the retina, optic disc, or iris, and angle structures in the front of the eye. PDR is associated with a high risk of visual morbidity arising from vitreous hemorrhage, traction retinal detachment, and neovascular glaucoma (Diabetic Retinopathy Research Group 1979).