Normal retinal blood vessels are watertight and do not leak. In diabetes, the retinal blood vessels can become damaged and develop tiny leaks. This is called nonproliferative diabetic retinopathy (NPDR). Blood and fluid seep from the leaks in the damaged retinal blood vessels, and fatty material (called exudate) can deposit in the retina. This causes swelling of the retina. When leakage occurs and causes swelling in the central part of the retina (the macula), it is called macular edema, and vision will be reduced or blurred.