The 'retina' is the film at the back of your eye, like the film in a camera. Light enters the eye and then passes through the eye to reach the retina. The messages about what you see are then passed on to the brain.
Retinopathy is the name given to 'disease of the retina'. Diabetic retinopathy occurs when the small blood vessels of the retina leak blood and other substances into the retina. Blindness from retinopathy can in theory be prevented. This can be done by regular eye checks and good blood sugar control.