If you have diabetes mellitus, your body does not use and store sugar properly. High blood-sugar levels can damage blood vessels in the retina, the nerve layer at the back of the eye that senses light and helps to send images to the brain. The damage to retinal vessels is referred to as diabetic retinopathy.

Types of Diabetic Retinopathy
There are two types of diabetic retinopathy: nonproliferative diabetic retinopathy (NPDR) and proliferate diabetic retinopathy (PDR).

NPDR, commonly known as background retinopathy, is an early stage of diabetic reinopahty. In this stage, tiny blood vessels within the retina leak blood or fluid. The leaking fluid causes the retina to swell or to form deposits called exudates.

Many people with diabetes have mild NPDR, which usually does not affect their vision. When vision is affected is the result of macular edema and/or macular ischemia.

PDR is present when abnormal new vessels (neovascularization) begin growing on the surface or the retina or optic nerve. The main cause of PDR is widespread closure of retinal blood vessels, preventing adequate blood flow. The retina responds by growing new blood vessels in an attempt to supply blood to the area where the original vessels closed.

Unfortunately, the new, abnormal blood vessels do not re-supply the retina with normal blood flow. The new vessels are often accompanied by scare tissue that may cause wrinkling or detachment of the retina.