What to do about diabetes-associated eye disease

I've written here about diabetes and eye disease before, so readers probably already know that diabetes is the leading cause of new cases of blindness in people ages 20 to 74. But you may not know as much as you should about the leading eye problems caused by diabetes—diabetes retinopathy, cataracts, and glaucoma. Here's information from Harvard Medical School's Special Health Report called Diabetes: A Plan for Living.

This condition affects the blood vessels in the retina, the back portion of the eye where images are captured and recorded. The retina converts light energy into electrical impulses and sends visual images to the brain along the optic nerve.

Scientists don't know what causes retinopathy, but they do know it occurs in two stages. In the first stage, the walls of the small blood vessels become abnormal and weaken. They leak fluid into surrounding tissue, leaving deposits of protein and fat called hard exudates. The vessels also develop microaneurysms, tiny bulges or pockets in their walls that tend to leak red blood cells into the retina. As the condition progresses, the abnormal vessels begin to close, robbing the retina of its blood supply. Nerve fibers die off because of poor circulation and lack of oxygen, creating white cottony patches known as soft exudates. These changes may not alter your vision. But if the fluid or blood leakage occurs near the macula — the part of the retina responsible for sharp, central vision — your sight will be impaired.

Severe impairment occurs when retinopathy advances to the proliferative stage, which is when the severely diminished blood flow causes the damaged retina to try to repair itself by sprouting new blood vessels. However, these new vessels grow abnormally and proliferate into the vitreous humor, the gel-filled compartment of the eye in front of the retina. The new vessels are fragile. When they bleed into the vitreous humor, they can block the passage of light and lead to a sudden loss of vision. The blood is usually reabsorbed, but scar tissue often forms. The scars in the vitreous humor can attach to the retina, pulling it away from the back of the eye. Retinal detachment can lead to permanent vision loss.

Detecting retinopathy requires a comprehensive eye exam. By dilating the pupil and using an ophthalmoscope, an instrument for examining the deep interior of the eye, a specialist can spot microaneurysms long before you notice any vision changes. The ophthalmologist may use other tests, too. Stereoscopic photography provides a detailed view of the retina. Fluorescein angiography involves photographing the eye after a dye has been given intravenously; the dye provides a detailed map of the retinal vessels, clearly revealing any leakage or areas of decreased blood supply.

People with type 1 diabetes should have an annual exam by an ophthalmologist within three to five years after diagnosis, while those with type 2 should see an eye specialist yearly as soon as they learn they have diabetes. Because of delayed diagnosis, about 10% to 20% of people with type 2 already have some degree of eye disease when their diabetes is diagnosed. Retinopathy can flare suddenly during pregnancy, so women with diabetes should schedule an eye exam early in their first trimester and be followed closely until three to six months after delivery. This isn't an issue for women with gestational diabetes.

Retinopathy is commonly treated with laser therapy. This procedure focuses a thin beam of high-energy light onto the retina, sealing the leaking blood vessels and destroying any new vessels. By stopping leakage near the macula when edema (the accumulation of fluid) is present, laser therapy can help prevent loss of visual acuity if it's performed early enough.

Laser surgery requires no incision, is relatively painless, and is done in a doctor's office. Treating proliferative retinopathy may require many laser "burns" over several treatment sessions. The goal is to destroy any retinal tissue that's not essential for vision, which reduces new vessel growth and shrinks the existing abnormal vessels. Treating macular edema requires far fewer burns and is usually done in one session. Because laser therapy destroys some eye tissue, peripheral and night vision may be diminished if many burns are required.

Steroid injections into the vitreous humor may also be used. This therapy provides only temporary relief, so multiple injections are often necessary. Major risks include a risk of developing glaucoma and, if multiple injections are used, an increased risk of cataracts.

If the retina is detaching or there's extensive bleeding and scarring, a vitrectomy may be necessary. This surgical procedure removes blood, scar tissue, and the vitreous humor. The detached retina is repaired, and the vitreous humor is replaced with saline solution. Although this is often effective, complications may include further retinal detachments or glaucoma.

People with diabetes tend to develop cataracts (a clouding of the eye's crystalline lens) more frequently and at a younger age than the general population. Cataracts progress slowly and painlessly, but you may notice your vision starting to blur or dim and find the glare from the sun or lights annoying. Cataracts are removed surgically when the impairment threatens your ability to perform routine activities. Implanting a new, artificial lens usually restores clear vision.

Glaucoma, a disorder characterized by excessive fluid pressure within the eyeball, is also more prevalent among people with diabetes. As with retinopathy, you may not be aware of the problem because there are no symptoms in the early stages. If glaucoma isn't detected and treated, usually with eye drops that reduce the pressure within the eye, the optic nerve can be damaged and blindness can ensue. Vision loss from glaucoma can't be restored, but the disorder can be controlled with medication. In some cases, laser surgery can improve fluid drainage.

Have you had an eye trouble since getting diagnosed with diabetes? What do you do to treat or prevent it?

Julie K. Silver, M.D., is an assistant professor in the Department of Physical Medicine and Rehabilitation at Harvard Medical School. She is also the Chief Editor of Books for Harvard Health Publications.

The Aging Eye

Four common eye diseases pose the greatest threats to vision after age 40: cataract, glaucoma, age-related macular degeneration, and diabetic retinopathy. The Aging Eye, a special health report from Harvard Medical School, will help you determine your risk of developing these disorders, describe their symptoms, and discuss diagnosis and treatment.

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