In PDR, large areas of the retinal blood vessels become obstructed causing the retina to lose its source of nutrition and oxygen. When this happens, peripheral, or side vision, is usually reduced, and the patient’s ability to see at night and to adjust from light to dark is often diminished.
As a result of this loss of nourishing blood flow, the retina responds by developing new blood vessels that are abnormal and are called neovascularization. The development of neovascularization is the retina’s attempt to compensate for the obstruction of its own blood vessels and the loss of nourishment. Many people with diabetes have some obstruction of the retinal blood vessels without ever developing neovascularization; but when neovascularization develops, it is dangerous to the eye. Neovascularization does not nourish the retina properly and may cause other problems. One problem is bleeding into the vitreous cavity called vitreous hemorrhage. A second problem is the growth of scar tissue on the retina. The scar tissue can pull the retina off the back wall of the eye. When this occurs, it is referred to as a traction retinal detachment. Either of these serious problems, vitreous hemorrhage or traction retinal detachment, can lead to severe loss of vision or even total blindness.