What causes diabetic retinopathy?

Uncontrolled Diabete. Diabetic retinopathy comes in two types non-proliferative or proliferative. Clinical trials such as the dcct, edic, ukpds, accord, ukpds-hds, field have shown that if glucose levels, blood pressure, cholesterol, and lipids are not controlled diabetic retinopathy can get worse and lead to severe vision loss. Trials such as the etdrs, drs, drvs show that eye physicians can delay blindness.
High blood sugar. Over many years causes the retinal blood vessels to be "leaky." fluid and blood collects in your retina and distorts your vision - this needs treatment. Also, new abnormal blood vessels can grow over the surface of the retina which can lead to bleeding and scarring with permamnet vision damage - this needs treatment too. The best treatment is prevention with good blood sugar control.