The form of diabetic retinopathy caused by leakage of retinal blood vessels is called nonproliferative diabetic retinopathy (NPDR). Another problem with retinal blood vessels in diabetes is that they can become blocked. If the retinal tissue no longer receives nutrition from the retinal blood vessels, it will stop working properly. The areas of the retina with obstructed blood vessels will foster the growth of abnormal new blood vessels, a process called neovascularization. Neovascularization can cause bleeding and scar tissue that may result in severe loss of vision or even blindness. The form of diabetic retinopathy in which neovascularization develops is called proliferative diabetic retinopathy (PDR). Both forms of the eye condition can occur together in an eye.

In diabetes, the retinal blood vessels can become damaged and develop tiny leaks. This is called nonproliferative diabetic retinopathy (NPDR). Blood and fluid seem from the tiny leaks, and fatty material (called exudates) can deposit on the retina, causing swelling of the retina. When this swelling occurs on the central part of the retina (the macula), it is called macular edema and vision will be reduced or blurred. A person with macular edema will usually experience some loss of vision. If one eye is affected, the other eye is also frequently affected. And if each macula is severely disturbed, central vision may be lost from each eye. Even if the ability to see detail has been lost from both eyes, a person with severe NPDR can usually learn to use areas just outside the macula to see some detail and perform everyday tasks. Early detection is a person’s best chance of saving their eyesight with laser surgery. Once the macula has been damaged, laser surgery is generally not helpful. For this reason, people with diabetes should test the vision of each eye, every day. One way to test vision is with the Amsler Grid.

Though vision may gradually become blurred, significant loss of sight does not usually occur with non-proliferative retinopathy. Since the patient does not experience pain or external symptoms such as bloodshot eyes or discharge, changes in the retina can go unnoticed unless detected by an eye exam. When bleeding occurs in proliferative retinopathy, the patient has clouding or complete loss of sight. Connective tissue pulling on the retina causes distortion and blurring. However, if abnormalities occur in the peripheral retina, the patient may not experience any symptoms.

In PDR, large areas of the retinal blood vessels become obstructed causing the retina to lose its source of nutrients. When this happens, peripheral vision is often reduced and the person’s ability to see at night or adjust their site to changes in lighting is often diminished. The retina will develop new, abnormal blood vessels in an attempt to compensate for its loss of nourishment. This is called neovascularization, and it is very dangerous to the eye. Neovascularization does not nourish the retina properly and may cause other problems such as bleeding into the vitreous cavity (called vitreous hemorrhage) or the growth of scar tissue on the retina, which can pull the retina off the back wall of the eye (called traction retinal detachment). Either of these severe problems, vitreous hemorrhage or traction retinal detachment, can lead to a severe loss of vision or total blindness.