NPDR is early damage to your eye-tiny blood vessels leak blood or fluid and exudates form. Many people with NPDR have normal vision, but when the most sensitive part of the eye is affected by macular edema (swelling) or macular ischemia (blood vessels closing leading to lack of blood and oxygen to the retina), vision is affected.
PDR is when abnormal new blood vessels (neovascularization) begin growing on the retina or optic nerve. The new blood vessels form due to ischemia, or lack of adequate blood flow. PDR causes more severe vision loss than NPDR because it can affect both central and peripheral vision.