Diabetic Retinopathy: A Leading Cause of Blindness in Adults

Diabetic retinopathy is the most common form of diabetic eye disease and a leading cause of new cases of blindness in American adults ages 20 to 74.

"It's very common, unfortunately, and with the rising epidemic of obesity and diabetes, we're seeing more and more of it," said Kimberly E. Stepien, MD. Dr. Stepien is a Medical College of Wisconsin Assistant Professor of Ophthalmology, Retina and Vitreous Surgery and practices at The Eye Institute of the Medical College of Wisconsin and Froedtert Hospital.

Early diagnosis and treatment are important in diabetic eye disease because intervention can prevent vision loss and blindness. "The good news is that we can usually treat diabetic retinopathy with lasers and other treatments," said Dr. Stepien. "We can potentially help prevent the retinopathy from progressing or actually cause it to regress."

A Complication of Type 1 and Type 2 Diabetes
People with diabetes have increased blood glucose (often called "blood sugar") levels, causing damage throughout the body. Normally, the pancreas releases the hormone insulin to controls glucose levels, but diabetics can't make enough insulin for good control.

Type 1 diabetes, or insulin-dependent diabetes, is usually first diagnosed in children, teenagers, or young adults. With this form of diabetes, the pancreas doesn't make any insulin at all and people must inject themselves with insulin in order to stay healthy.

Type 2 diabetes, or noninsulin-dependent diabetes, is the more common form of diabetes. This form of diabetes usually begins with insulin resistance, a condition in which fat, muscle, and liver cells do not use insulin properly. Type 2 diabetes can sometimes be controlled with diet and exercise, but many people with Type 2 will eventually have to take oral or injected insulin.

Diabetic retinopathy is a direct complication of diabetes. In diabetic retinopathy, elevated blood sugar levels cause retinal blood vessels to break down, leak or become blocked. (The retina, the light-sensitive nerve tissue at the back of the eye, is vital to good vision.)

Early symptoms of diabetic retinopathy can go unnoticed, said Dr. Stepien. "Early on, diabetic retinopathy has few or no symptoms. Changes are only seen on a dilated clinical eye exam in which the retina is examined. Changes include tiny hemorrhages on the back of the eye, accumulation of exudates in the back of the eye, and swelling from leakage of the blood vessels on the back of the eye.

"As the disease progresses, the blood vessels in the back of the eye can start leaking, can become blocked and new blood vessels can start growing, something we call neovascularization. When these changes occur, it's much more worrisome. This stage of the disease is called proliferative diabetic retinopathy (PDR), and the risk of losing vision from diabetic retinopathy is much higher. So, the key is screening and prevention."

Progression of Retinopathy
According to the National Eye Institute, diabetic retinopathy has four stages:

1. Mild Nonproliferative Retinopathy. At this earliest stage, microaneurysms occur. They are small areas of balloon-like swelling in the retina's tiny blood vessels.

2. Moderate Nonproliferative Retinopathy. As the disease progresses, some blood vessels that nourish the retina are blocked.

3. Severe Nonproliferative Retinopathy. Many more blood vessels are blocked, depriving several areas of the retina with their blood supply. These areas of the retina send signals to the body to grow new blood vessels for nourishment.

4. Proliferative Retinopathy. At this advanced stage, the signals sent by the retina for nourishment trigger the growth of new blood vessels. This condition is called proliferative retinopathy. These new blood vessels are abnormal and fragile. They grow along the retina and along the surface of the clear, vitreous gel that fills the inside of the eye. By themselves, these blood vessels do not cause symptoms or vision loss. However, they have thin, fragile walls. If they leak blood, severe vision loss and even blindness can result.

Screenings Important for Early Diagnosis
An annual eye exam which includes dilation is important to detect diabetic retinopathy early so that treatment can begin. "People with diabetes need a dilated screening exam at least once a year. At some eye exams, a patient may not necessarily get dilated for a variety of reasons. If there isn't a doctor actually looking into the back of the eye, it's unlikely they will see the diabetic changes," Dr. Stepien said.

According to the National Institutes of Health, people with diabetes should have a dilated eye examination annually, and it's important that an optometrist or ophthalmologist conduct the exam.

People with Type 1 diabetes should be screened for diabetic eye disease within three to five years of their initial diagnosis. The longer a patient has diabetes, the more likely he or she will develop diabetic retinopathy. Studies tracking the progression of diabetic retinopathy have shown that 20 years after diagnosis, nearly 100% of people with Type 1 diabetes will have some form of retinopathy, Dr. Stepien said. "Some of those can be mild changes. Some can be very severe."

People diagnosed with Type 2 diabetes should be screened at the time of diagnosis, Dr. Stepien said. "With Type 2 diabetes, you might not get diagnosed until you've had diabetes for several years. People can have really high blood sugars and not be aware of it unless they're screened, usually by their primary care doctor," she noted. "I've seen multiple patients with Type 2 diabetes who didn't realize they had diabetes until they saw their primary care provider, and they came in with significant diabetic retinopathy."

Type 1 diabetes Dr. Stepien said, usually presents as an acute medical situation, but in Type 2, diabetes has a more gradual onset.

Treatments for Diabetic Retinopathy
Controlling diabetes and blood sugar levels is one way to prevent or treat diabetic retinopathy. "Multiple studies have shown that the tighter control of your blood sugars, the less likely the diabetic retinopathy is to occur or to progress," said Dr. Stepien. "Good control of your blood pressure and cholesterol is also important. The best way to treat diabetic retinopathy is to prevent it from occurring."

Laser treatment is often recommended to treat diabetic retinopathy. The laser is focused on the retina and can seal off leaking blood vessel or cause abnormal new vessels to shrink and may prevent them from re-growing.

"Right now, the gold standard is to do laser treatment," said Dr. Stepien. "But not everyone responds to the laser. There are a many trials going on looking at different medications to treat diabetic retinopathy."

According to the National Institutes of Health, early detection and treatment can prevent or delay blindness due to diabetic retinopathy in 90% of people with diabetes.

Melissa Rigney Baxter
HealthLink Contributing Writer

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.