Diabetic retinopathy is a complication of diabetes caused by damaged blood vessels in the tissue of the eye's retina. Too much sugar in the blood can cause the small blood vessels that lead to the retina to be blocked. There are two types of diabetic retinopathy - nonproliferative diabetic retinopathy (NPDR), in which vessels in the retina have tiny bulges, leak and don’t grow correctly, and advanced (proliferative) diabetic retinopathy, where vessels are blocked completely and new, non-working vessels form, causing fluid to build-up (glaucoma). Symptoms may not appear at first, but as the disease progresses, blurred vision, dark spots, and vision loss can happen.