Encyclopedia - Diabetic Retinopathy

What is nonproliferative diabetic retinopathy?
How is nonproliferative diabetic retinopathy treated?
What causes proliferative diabetic retinopathy?
How is proliferative diabetic retinopathy treated?
How can diabetic eye disease be prevented?

Diabetes can attack the eyes in several ways. For example, it increases the risk of glaucoma and cataracts. But primarily it affects the retina, the light-sensitive membrane at the back of the eye (See Anatomy of the Eye), causing a variety of problems that are collectively called diabetic retinopathy.

The disease occurs most frequently in Type I, or early-onset, diabetes, in which the insulin-making cells of the pancreas are destroyed so that regular infusions of insulin are needed. However, it also occurs in more common Type II, or noninsulin-dependent, diabetes, in which the body's production or use of insulin declines with age.

What is nonproliferative diabetic retinopathy?

Diabetes causes deterioration of the small blood vessels of the eye -- specifically, in the cells that line the interior of those blood vessels, the basement membrane, the endothelial cells that lie above them, and the pericytes, which are supporting cells. The basement membrane becomes thicker and the number of pericytes decreases, so the blood vessels begin to leak.

This results in a condition called nonproliferative diabetic retinopathy. One effect of the disease is formation of microaneurysms, bulges that can leak fluid into the retina. This leakage can cause macular edema, the most common cause of diabetic visual impairment. In this disease, the extremely sensitive central area of the retina, the macula, deteriorates. Central vision becomes worse, so reading and other functions are impaired.

How is nonproliferative diabetic retinopathy treated?

Macular edema can be treated by a relatively new technique called photocoagulation, in which argon laser light is used to weld the leaking blood vessels. The light can be beamed at specific small vessels or, if leakage is widespread, at a large number of vessels. Laser treatment can stop the deterioration, but it cannot restore vision loss, so early detection is essential.

Other kinds of damage caused by nonproliferative diabetic retinopathy include:

dot hemorrhages -- very small areas of bleeding
blot hemorrhages -- larger areas of bleeding
cotton wool spots -- blockage of tiny retinal blood vessels

What causes proliferative diabetic retinopathy?

Another form of diabetic eye damage is proliferative diabetic retinopathy, an overgrowth of new blood vessels in the retina. This overgrowth generally happens years after diabetes has been diagnosed.

Although the reason for the proliferation of these retinal blood vessels is unknown, it is believed to be the body's response to the damage that diabetes causes to existing blood vessels. The new blood vessels are abnormally flimsy, and their growth is not under normal controls, so they leak blood and can grow through the retina into the vitreous gel that fills the eye.

The vessels are so leaky that even normal head movements, such as a sneeze or the rapid eye movement (REM) that occurs during sleep, can cause them to break and hemorrhage. The resulting hemorrhages can send blood into the retina, the area between the retina and the vitreous gel, or the vitreous. The result can be a blind spot in part of the visual field or spots and cobwebs that progressively impair vision. In the worst-case scenario, vitreous hemorrhage can cause blindness.

The body does respond to these hemorrhages, with a natural cleaning effort to remove the blood from the retina or vitreous. But this response can also cause damage, by producing scar tissue. Sometimes scar tissue can break away, attaching itself to other parts of the retina or optic disc. Or scar tissue can contract, causing a retinal detachment. In the worst case, a retinal detachment in the macula causes permanent, severe vision loss.

How is proliferative diabetic retinopathy treated?

Proliferative diabetic retinopathy can also be helped by laser treatment. This treatment usually requires many more bursts of laser light than used for the nonproliferative form of diabetic retinopathy. Up to 2,000 bursts may be needed, in two or three sessions. This laser treatment causes the formation of artificial scars, which help prevent severe loss of vision in many patients.

Vitreous hemorrhage can be treated by a technique called vitrectomy, which uses specially designed instruments to remove the area of hemorrhage. Laser therapy or cryotherapy, using extreme cold, can be applied during vitrectomy to improve the effectiveness of the treatment.

How can diabetic eye disease be prevented?

As with any complication of diabetes, the best treatment is prevention. Many studies have shown that effective control of blood sugar levels, by insulin therapy in Type I diabetes and by dietary measures and medications in Type II diabetes, delays the onset and slows the progression of retinopathy. Controlling blood pressure and weight, and treating infections promptly also reduce eye problems and other diabetic complications. Regular eye examinations are recommended for all diabetics.

The American Academy of Ophthalmology recommends the following schedule of eye examinations for diabetics:

For persons who contract diabetes before reaching age 30 -- a first eye examination five years after diagnosis, with annual exams hereafter and more often if symptoms of trouble develop
When diabetes is diagnosed when a person is more than 30 years old -- an eye examination as soon as the diagnosis is made, with annual eye examinations thereafter

Pregnancy is a special case. An examination is recommended before conception for diabetic women who are attempting to become pregnant, and early in the first trimester when pregnancy occurs, with a follow-up examination three months later.