Diabetic retinopathy is the most common type of diabetic eye disease and the leading cause of blindness in the US. This condition is caused by blood vessel changes within the retina that lead to swelling and leaking of fluid. It can also cause growth of abnormal new blood vessels on the surface of the retina. There are four stages of diabetic retinopathy, starting with the occurrence of microaneurysms (blood vessels that swell and leak) and ending with the development of abnormal blood vessels on the retinal surface. These blood vessels can easily leak fluid, causing severe vision loss and even blindness.
Sometimes, the fluid from abnormal blood vessels leaks into the center of the macula (the center of the retina) and causes swelling and blurred vision. This condition is called macular edema. The risk of developing macular edema increases as diabetic retinopathy progresses.