Eye Disease - Long Term Complications: Diabetes

Content provided by the Faculty of the Harvard Medical School

Eye disease

Diabetes increases your risk for vision loss fourfold, and it's the leading cause of new cases of blindness in people ages 20–74. Although most of the harm is caused by damage to the retina (retinopathy), diabetes also makes cataracts and glaucoma more likely.

Diabetic retinopathy

This condition affects the blood vessels in the retina, the back layer 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. After 20 years, nearly all people with type 1 diabetes and 60% of those with type 2 diabetes have developed retinopathy. By that time, half of all people with type 1 diabetes and 10% of those with type 2 diabetes have the more serious, advanced form, known as proliferative retinopathy. However, tighter glucose control should substantially decrease these numbers in the future.

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 due to 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

Early detection and treatment are essential to preventing vision loss and blindness. However, this isn't as simple as it sounds. In its early stages, retinopathy usually has no warning signs or symptoms.

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 beginning 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%–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.

Treating retinopathy

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 blindness 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.

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 is replaced with saline solution. Although this is often effective, complications may include further retinal detachments or glaucoma.

Cataracts and 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.

Preventing eye disease

One of the best ways to protect your vision is to control your blood glucose levels tightly. The Diabetes Control and Complications Trial, and a long-term study following it, found that people who keep their blood sugar at near-normal levels cut their risk of developing eye diseases and macular edema by 75%. Retinopathy was also less likely to progress among those who had tight control over their diabetes.

Other steps can help, too. Controlling your blood pressure can keep retinopathy at bay, and an annual eye exam should be a high priority.

Last updated:	January 23, 2007