The retina is the inside lining behind each Eye. The retina senses light and turns it into signals that your brain decodes, so you probably can see the world around you. Damaged blood vessels can hurt the retina, causing a illness called diabetic retinopathy. If your blood glucose stays excessive over time, it could injury the tiny blood vessels behind your eyes. This injury can begin throughout prediabetes, when blood glucose is greater than regular, but not excessive sufficient so that you can be diagnosed with diabetes.