Diabetic retinopathy, which affects more than four million Americans age 40 and older, is the most common eye complication of diabetes. Almost everyone with type 1 diabetes and more than 70 percent of people with type 2 disease will eventually develop retinopathy—in most cases without experiencing any vision loss. However, diabetic retinopathy can cause blindness and is the most frequent cause of new cases of blindness in adults ages 20–74.
The word "retinopathy" refers to damage in the retina, the light-sensitive nerve tissue at the back of the eye that transmits visual images to the brain. The damage is caused by changes in the tiny blood vessels that carry blood to the retina.
In the early stages—called nonproliferative retinopathy—these blood vessels weaken and develop bulges that may leak blood or fluid into the surrounding tissue. Vision is rarely affected during this stage. But if your diabetes isn't tightly controlled, eye damage is likely to get worse. Fragile new blood vessels may begin to grow on the retina and into the vitreous humor (the gel-like substance inside the back of the eye). This condition is called proliferative retinopathy.
The abnormal blood vessels often rupture and bleed into the vitreous humor, causing blurred vision or temporary blindness. Scar tissue resulting from the bleeding can pull the retina away from the back of the eye (a condition called retinal detachment), which may cause permanent vision loss.
At any stage of retinopathy, fluid may accumulate around the macula, the most sensitive portion of the retina and crucial for seeing fine detail. This condition, called macular edema, causes severe blurring of vision.
Prevention of retinopathy
If you have diabetes, you should see an ophthalmologist (eye doctor) every year for an eye examination, during which special eyedrops are used to open (dilate) your pupils. This allows the doctor to get a better look at the retina to detect any damage when the disease is in its early, treatable stages and to monitor progression of the disease. People with type 1 diabetes should have an initial eye exam within three to five years of the onset of diabetes. People with type 2 diabetes should start annual eye examinations when their diabetes is first diagnosed.
Keeping your blood pressure below 130/80 mm Hg can help prevent the onset and progression of damage to the retina. Some—but not all—studies indicate that lowering blood cholesterol levels and quitting smoking may be helpful as well. However, the most important way to prevent diabetic retinopathy or keep it from getting worse is to maintain tight blood glucose control. For example, in the Diabetes Control and Complications Trial (DCCT), people with type 1 diabetes who injected insulin multiple times each day or used an insulin pump had a 76% lower risk of developing diabetic retinopathy and a 54% lower risk that existing retinopathy would worsen than people who followed a less rigorous treatment program.
In addition, the United Kingdom Prospective Diabetes Study (UKPDS) showed that people with type 2 diabetes who controlled their blood glucose levels with medication were 30% less likely to have retinopathy that required laser treatment than people who relied on diet and exercise alone.
Treatment of retinopathy
One of the major reasons why annual vision exams are so important is that proliferative retinopathy can be effectively treated with laser photocoagulation procedures, but only if it is detected early. Prompt treatment can also preserve vision following a retinal detachment. However, laser photocoagulation surgery won't help if vision is already impaired.
Laser photocoagulation is an outpatient procedure in which an ophthalmologist dilates the pupils of your eyes. The doctor then aims bursts of laser light at a series of points on the retina, causing tiny scars to form. The procedure prevents small vessels from rupturing and bleeding into the vitreous humor. Although extensive photocoagulation usually diminishes peripheral vision and may decrease night vision, its success in preserving visual acuity makes it worthwhile.
If the extent or location of the retinopathy makes photocoagulation ineffective or if the vitreous humor of the eye is too clouded with blood, vision may be improved with vitrectomy, a surgical procedure that removes the vitreous humor and replaces it with a saline solution. Roughly 70 percent of people who undergo vitrectomy notice an improvement in or stabilization of their eyesight, and some recover enough vision to resume reading and driving.