There's nothing at all sweet about the "sugar disease."

A few generations ago, people didn't associate diabetes mellitus with blindness because few people with the disease lived long enough to go blind. Today, however, when medical treatment allows most diabetics to live a normal life span, we realize that diabetes can lead to diabetic retinopathy, the leading cause of new blindness for people over the age of 20 in North America. According to the U.S. Department of Health and Human Services, people with diabetes are 29 times more likely to go blind than those without diabetes. And that's a lot of potential victims: It's estimated that there are approximately 11 million diabetics in the United States alone. That's the bad news. The good news is that if diabetic retinopathy is caught in time, it can often be stopped.

There are two types of diabetes: diabetes insipidus, which stems from a problem with the pituitary gland, and diabetes mellitus, which is the more common and more dangerous form. Although the two diseases are unrelated, two of the symptoms are the same for both. People with either are excessively thirsty and urinate a lot.

We will be dealing with diabetes mellitus in this article because it is the one that can lead to eye problems. People with this condition have trouble using and storing blood sugar or glucose. Typically they have elevated blood sugar levels, and their blood vessels undergo harmful changes as a result.

Although no one is sure what causes diabetes mellitus, there are indications that it is linked to problems that develop when a person's pancreas fails to produce enough insulin, or when the body fails to use the insulin properly. Insulin is a natural hormone that the body depends on to utilize carbohydrates.

A lack of insulin will cause a buildup of sugar in the bloodstream. This excess is excreted through the urinary tract.

Diabetes mellitus is usually divided into two types: noninsulin-dependent diabetes and insulin-dependent diabetes. The first type is considered less severe. It can often be controlled with the right diet and proper lifestyle. Exercising, maintaining proper weight, and cutting down on sugar can all help.

As the name implies, people with insulin-dependent diabetes mellitus usually require insulin. The type of insulin and dosage varies from person to person. Today it is not uncommon to develop either kind of diabetes well after age 20.

Taking Aim at the Eyes

The effect that diabetes has on the sufferer's blood vessels also varies from individual to individual. Diabetic retinopathy occurs when the blood vessels that feed the retina begin to deteriorate. Once damaged by the disease, these blood vessels may leak blood or other fluid. They might become enlarged. They might even develop fragile, brushlike branches. Or all three might happen.

The disease seems to effect the eyes in another way too: There is a slightly higher incidence of cataracts in people with diabetes. Diabetics can also expect to wait a little longer for their eyes to heal after cataract surgery.

Although no one can predict what exactly will happen—or if the problems the disease causes will be major or minor—doctors know that the longer you have diabetes, the more likely you are to have diabetic retinopathy.

According to the American Academy of Ophthalmology, about 50 percent of all people who have had diabetes for more than 10 years have some blood vessel damage in their eyes. The odds of developing diabetic retinopathy increase the longer you live. After 20 years with diabetes, the likelihood is over 90 percent. Obviously, diabetic retinopathy is a major problem for those who become diabetic as children.

It is often said that diabetics who keep their blood sugar levels under control are less likely to develop eye problems than those who can't seem to get them in line. But we aren't sure if that's true, and if it is, why.

But we do know that diabetic retinopathy is very likely to hit the so-called brittle diabetics—those whose blood sugar is hard to regulate with the proper amount of insulin and who are prone to all the other related afflictions such as ulcers on the feet, kidney problems, and diabetic coma.

The Two Forms of Retinopathy

Luckily, not all people with diabetic retinopathy advance to the more serious stage of blindness. Most of the eye problems they do develop are the result of background retinopathy, the first of two stages of the disease.

Background Retinopathy

Background retinopathy is a mild form of diabetic retinopathy. Luckily, it does not cause a major loss of vision, and in about 80 percent of cases it does not progress to a more severe type of retinopathy.

In background retinopathy, vision can dim or blur because the tiny blood vessels within the eye begin to change. Some vessels close off. Some shrink. Some enlarge and form balloonlike sacs that collect blood and obstruct normal blood flow. Some leak either blood or other fluid, forming deposits, called exudates, on the surface of the retina itself or producing swelling within the retina. The blood vessels can also develop microaneurysms, tiny outpouchings of the blood vessel wall, which look like tiny dots of blood just sitting on the surface of the retina.

Sometimes these dots and exudates disappear or change locations on their own. Sometimes they don't.

The damage that background retinopathy can do is usually determined by how much leakage there is, where it collects, and how long it stays there without treatment. The damage can be much worse if the leaking blood vessels affect the macula, the central portion of the retina that provides central vision. The macula lets us see fine details, as well as all the things that are directly in front of us. If much of the macula is blocked, you could lose your ability to read, drive, or do close work.

Proliferative Retinopathy

Proliferative retinopathy is like background retinopathy, only worse—in some cases, much, much worse.

In the advanced or proliferative stage, new blood vessels can grow inside the eye. Some may grow over the surface of the retina itself or grow on the iris and cause a form of glaucoma.

Large pockets of leaking fluid or blood can collect in the vitreous, the jellylike material inside the eye, blocking or distorting the retina's view of the outside world.

Sometimes the fluid is reabsorbed naturally into the body and the vitreous clears on its own. In other cases, however, surgery is required.

Diagnosing the Problem

An ophthalmologist is the best person to tell you if you have either background or proliferative retinopathy. Some cases of background retinopathy are so mild—at first—that you might not even be aware that you have a problem. Because retinopathy can get worse, diabetics should have their eyes checked by an ophthalmologist regularly.

Your ophthalmologist will first examine the interior of your eyes with an ophthalmoscope. The doctor might also photograph the interior of the eye for more careful study. Many doctors keep a regular file of eye photographs so they can see how the patient's eye changes over time.

If there are indications that you might have diabetic retinopathy, the doctor will perform a fluorescein angiography. In this test, a dye is injected into your arm so that it will travel throughout the bloodstream, including the blood vessels in the eye.

A series of rapid photographs are taken as the dye passes through the blood vessels of the retina and choroid. This test can not only confirm the presence of retinopathy, it also shows exactly how far it has progressed. By the way, a fluorescein angiogram is a photographic process, not an x-ray, so there is no radiation to worry about.

What about Treatment?

One of the best things diabetics can do for their eyes is take care of the rest of their body by following the proper diet, maintaining correct weight, and taking any prescribed medication. They should carefully follow their physician's advice, especially in regard to exercise. Diabetics with background retinopathy should have few problems with exercising. But those with proliferative retinopathy should exercise with moderation and caution and avoid straining or leaning over with the head down.

Usually, background retinopathy doesn't require treatment. It's only when it crosses the line and becomes proliferative that anything can—or should—be done. But in all cases it is best to consult your doctor in identifying and treating problems.

There are two treatments for proliferative retinopathy. The primary and most effective treatment for proliferative retinopathy is a laser treatment called panretinal photocoagulation. It cannot, however, be used in all cases. If, for example, the damaged blood vessels are over the macula, treating the macula with the laser could destroy it. But the laser can be used successfully in many other cases.

Despite the heat that the laser generates, the treatment is usually painless. The procedure is similar to the one used for glaucoma. The same argon laser is used. For glaucoma, it's aimed at the trabecular meshwork. For proliferative retinopathy it is aimed at the problem blood vessels.

Why does the laser work? Doctors don't know exactly. But we can make some educated guesses.

One theory is that burning and cauterizing the defective blood vessels redirects or changes the pattern of blood flow in the retina back to normal. Another theory states that, with retinopathy, there may be a relative lack of blood supply to the retina. By killing off some of the tissue, the laser reduces the amount of blood flow that the retina needs, so that demand and supply more closely match. Whichever theory ultimately proves correct, the important thing is that panretinal photocoagulation almost always works.

In just 3 to 4 percent of cases, laser treatment fails to improve the eye condition. For those few restricted cases, a doctor may choose to perform a vitrectomy. After making incisions in the sides of the eye, a small surgical instrument is inserted inside. The instrument chops and gobbles up the blood clots or scar tissue that were clouding the patient's vision. The clouded vitreous is then replaced with a sterile, clear solution that is absorbed by the body as more vitreous is regenerated.

Regardless of the treatment method employed, the important thing to keep in mind is that with early diagnosis and care you can save your eyes.

Eric Rost

Copyrighted material; do not reprint without permission.

 

View all articles by Eric Rost