Diabetes Forecast

Combating Retinopathy

Prevention is crucial in keeping your eyes healthy

By Erika Gebel, PhD ,

Fundamentally, the job of the eye is to distinguish light from dark. In humans, eyes also reveal a world of incredible detail, courtesy of nerves, blood vessels, light-sensing molecules, and highly evolved regions of the brain.

Unfortunately, these delicate spheres are also susceptible to injury, and eye disease is one of the major complications of uncontrolled diabetes. The most common diabetic eye disease is retinopathy, which in severe forms causes blindness in 10,000 people with diabetes each year. Between 40 and 45 percent of Americans with diabetes have some degree of retinopathy. Glaucoma and cataracts are also eye diseases that disproportionately affect people with diabetes.

By the time symptoms of eye disease appear, it may be too late to reverse the damage. This is why it's so important for people with diabetes to have their eyes checked regularly. While prevention is the best approach, there are effective ways to treat diabetic eye disease, particularly in its early stages.

A Delicate Orb

The eye is a jelly-filled sphere connected to the brain via the optic nerve. The front side, facing the world, is protected by the tough cornea. Behind this shield is the colorful and muscular iris, which surrounds the darker-colored pupil. The iris can squeeze or relax to change the size of the pupil and thus the amount of light that enters the eye.

Behind the pupil is a lens, which focuses light before it shines on the retina that lines the eye's inner back wall. Molecules within the retina convert light and color information into electrical signals that are sent to the brain, where they are instantly decoded and turned into images. The part of the retina that is responsible for seeing fine details—like the letters on this page—is called the macula.

The retina is nourished by many tiny blood vessels called capillaries. Diabetes can damage these capillaries, leading to retinopathy. Scientists are still trying to figure out how this happens; faulty signaling, oxidative stress, out-of-control growth, and the direct modification of blood vessels by glucose are all suspected of causing the damage.

The Major Maladies

There are two main types of retinopathy: nonproliferative and proliferative. Nonproliferative retinopathy, the more common variety, is marked by the swelling of blood vessels. This may disrupt the transfer of nutrients and other molecules between a blood vessel and the eye. While generally not dangerous, nonproliferative retinopathy can suddenly threaten one's sight if blood leaks from a strained vessel near the macula. If the macula swells with fluid—a condition called macular edema—vision may become blurred or entirely lost.

Sometimes nonproliferative retinopathy becomes proliferative, which is more destructive. Proliferative retinopathy damages capillaries so much that they shut down, triggering the growth of abnormal new blood vessels. The new capillaries tend to leak or cause scar tissue to form, both of which can lead to vision loss. Scar tissue may distort the retina, triggering a condition called retinal detachment.

Glaucoma stems from a buildup of eye pressure that cuts off blood vessels linking the retina and the optic nerve. While glaucoma isn't as closely associated with diabetes as retinopathy is, people with diabetes are 40 percent more likely to develop glaucoma than those without. Cataracts, a clouding over of the lens that blocks sight, are a common part of getting older, but diabetes seems to cause them at a younger age. People with diabetes under 60 years old are three to four times as likely to develop cataracts as those without diabetes.

Spotting Symptoms

Early detection and treatment are keys for preventing vision loss in people with diabetic eye disease. A common symptom is blurred vision, which can be caused by macular edema or blood vessel growth on the retina. Leaky blood vessels may make floating spots appear or increase in the field of vision. Even though blurred vision or spots may go away, these symptoms require a prompt checkup by a doctor familiar with diabetic eye disease. Failing peripheral vision may signal glaucoma, while overall blurriness could indicate cataracts.

The American Diabetes Association recommends that people over 10 years old with type 1 diabetes should have a comprehensive eye exam within five years of diagnosis and then each year. People with type 2 should be tested shortly after diagnosis (since many will already have had diabetes for years) and then annually. Pregnant women with preexisting diabetes are at particular risk for eye disease, and ADA recommends an examination during the first trimester of pregnancy.

During an eye exam, the doctor will test vision, check eye pressure, and dilate the pupils to allow a thorough inspection of the retina and optic nerve. Sometimes a doctor injects a special dye into a patient's arm that travels to the eyes, making the blood vessels easier to examine.

Getting Treatment

People who have had diabetes longer, are older, and have poor blood glucose control are all more likely than others to get diabetic eye diseases. High blood pressure is thought to worsen retinopathy, because it stresses the capillaries in the eyes. Studies show that optimal control of blood glucose and blood pressure can reduce the risk of developing retinopathy or slow its progression.

If nonproliferative retinopathy is detected, the first step is usually to get blood glucose and blood pressure under control. If macular edema or proliferative retinopathy is discovered, prompt treatment is needed. Laser photocoagulation, which can "burn" damaged blood vessels shut, is the most common therapy. Another treatment option for severe bleeding is a vitrectomy, surgery that removes some or all of the gel-like vitreous humor from the eye. Glaucoma may be treated with medication, lasers, or surgery. Treatment for severe cataracts involves removing the eye's lens and replacing it with an artificial one.

Vision problems are far from inevitable. By getting regular medical checkups and keeping a sharp eye on blood glucose control, people with diabetes can greatly up their odds of a life full of seeing the sights.



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