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Diabetic Retinopathy

by Sunir J. Garg, MD, FACS

Diabetic retinopathy is damage to the retina (the transparent, light-sensitive structure at the back of the eye) as a result of diabetes.

  • Blood vessels in the retina can leak blood and fluid.

  • New blood vessels may develop, sometimes leading to bleeding, scar formation, or retinal detachment.

  • The diagnosis is based on an eye examination after the pupil is dilated with eye drops.

  • Controlling blood sugar and blood pressure is important for people who have diabetic retinopathy or who are at risk of developing it.

  • Laser treatments and injections into the eye can usually decrease leakage of blood and fluid from blood vessels, thus preventing or delaying further damage.

Diabetes mellitus is among the leading causes of blindness in the United States and other developed countries, particularly among working-age adults. After several years, some retinal change occurs in almost all people with diabetes, regardless of whether they use insulin therapy. People with diabetes who also have high blood pressure are at much higher risk of developing diabetic retinopathy because both conditions tend to damage the retina. Pregnancy can cause diabetic retinopathy to worsen.

Repeated exposure to high levels of sugar (glucose) in the blood make the walls of small blood vessels, including those in the retina, weaker and, therefore, more prone to damage. Damaged retinal blood vessels leak blood and fluid into the retina.

The extent of retinopathy and vision loss is related mostly to the following:

  • How well blood sugar levels are controlled

  • How well blood pressure is controlled

  • How long the person has had diabetes

In general, retinopathy appears 5 years after people develop type 1 diabetes. Because diagnosis of type 2 diabetes may not occur for years, retinopathy may be present by the time people receive the diagnosis of type 2 diabetes.

Symptoms

Diabetes mellitus can cause two types of changes in the eye. Nonproliferative diabetic retinopathy occurs first. Proliferative diabetic retinopathy occurs after nonproliferative diabetic retinopathy and is more severe.

Nonproliferative diabetic retinopathy

In nonproliferative diabetic retinopathy, small blood vessels in the retina leak fluid or blood and may develop small bulges. Areas of the retina affected by leakage may swell, causing damage to parts of the field of vision. At first, the effects on vision may be minimal, but gradually vision may become impaired. Blind spots may occur, although these may not be noticed by the person and are usually discovered only if testing is done. If leakage occurs near the macula, the central vision may be blurry. Swelling of the macula (macular edema) due to leakage of fluid from blood vessels can eventually cause significant loss of vision. However, people may not have vision loss even with advanced retinopathy.


Proliferative diabetic retinopathy

In proliferative diabetic retinopathy, damage to the retina stimulates the growth of new blood vessels. The new blood vessels grow abnormally, sometimes leading to bleeding (hemorrhage) or scarring. Extensive scarring may cause retinal detachment (see Detachment of the Retina). Proliferative diabetic retinopathy tends to result in greater loss of vision than does nonproliferative diabetic retinopathy. It can result in total or near-total blindness due to a large hemorrhage into the vitreous humor (the jellylike substance that fills the back of the eyeball, also called the vitreous) or to a type of retinal detachment called traction retinal detachment. Growth of new blood vessels can also lead to a painful type of glaucoma (neovascular glaucoma). Macular edema can cause significant loss of vision. Symptoms of proliferative diabetic retinopathy may include blurred vision, black spots or flashing lights in the field of vision, and sudden, severe, painless vision loss.


Diagnosis

Doctors diagnose nonproliferative and proliferative diabetic retinopathy by examining the retina with an ophthalmoscope. Doctors do fluorescein angiography (see see Tests for Eye Disorders : Angiography) to help determine the location of the leakage as well as areas of poor blood flow and the areas of new abnormal blood vessel formation, determine the extent of retinopathy, develop a treatment plan, and monitor the results of treatment. Doctors take color photographs of the retina during fluorescein angiography. Optical coherence tomography, an imaging study, can help assess the severity of macular edema and assess how well the person is responding to treatment.

Prevention

The best way to prevent diabetic retinopathy is to control blood sugar and keep blood pressure at normal levels. People with diabetes should have an annual eye examination, in which the pupil is dilated with eye drops, so that retinopathy can be detected and any necessary treatment can be started early. Pregnant women with diabetes should have these eye examinations about once every 3 months.

Treatment

Treatment is aimed at controlling blood sugar and blood pressure. People with macular edema are given eye injections of certain drugs (for example, ranibizumab, pegaptanib, bevacizumab, or occasionally triamcinolone). Treating macular edema may improve vision. Other treatments include laser photocoagulation, in which a laser beam is aimed into the eye at the retina to slow the growth of abnormal new retinal blood vessels and decrease leakage. Laser photocoagulation may need to be repeated. If bleeding from damaged vessels has been extensive, a procedure called vitrectomy may be needed. In this procedure, blood is removed from the cavity in which the vitreous humor lies. Vision often improves after vitrectomy for vitreous hemorrhage, and vision may improve after vitrectomy for traction retinal detachment. Laser treatment only rarely improves vision, but it commonly prevents further deterioration. Newer treatments that are being investigated involve inserting an implant in to the eye that delivers constant levels of a corticosteroid.

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  • MACUGEN
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