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Diabetes mellitus is a condition in which the blood sugar level is elevated because the body is unable to use and store sugar. As a result, the blood's high sugar content damages capillaries, the tiny blood vessels connecting arteries and veins. In addition, diabetes can cause changes in various body organs, including the kidneys and the eyes.

How Diabetes Causes Retinal Damage

Some people are unaware that they have diabetes. Blurred vision from diabetic retinopathy might be the first symptom of the disease.

For most, however, there are no signs of retinopathy for at least five years after the onset of the diabetes. The longer someone has diabetes, the more likely they will develop retinopathy. After 25 years, nearly all diabetics show at least some minor signs of retinopathy. Only a small number, however, will have a significant decrease in vision, and a still smaller number will become blind.

Two Types of Retinopathy

There are two types of retinopathy: background, or nonproliferative, retinopathy and proliferative retinopathy. In background retinopathy, most of the early damage is done to retinal capillaries. Some become blocked, while others develop balloon-like swellings called "micro-aneurysms." These and other weak spots leak excessive fluid into the retina, causing swelling. Some capillaries can break, triggering retinal hemorrhages.

Many patients never progress beyond background retinopathy. Some, however, develop so many capillary blockages that the retina does not get enough oxygen. This leads to proliferative diabetic retinopathy. Oxygen deficiency stimulates the growth of new, or extra, blood vessels on the surface of the retina and optic nerve. These vessels are fragile and leak blood or fluid into the vitreous, causing it to shrink toward the front of the eye and pulling the blood vessels behind it.

Hemorrhages into the vitreous are perceived as floaters or "cobwebs" and vision is hazy. A dense vitreous hemorrhage may cause a severe decrease in vision. In some cases, as the vitreous shrinks, it might pull part of the retina from its normal position. This is called retinal detachment. Further, if the retina's circulation is severely abnormal, surplus blood vessels may form on the iris, leading to a severe form of glaucoma.

If you believe you are experiencing a vitreous hemorrhage, you should seek immediate attention.

Evaluating Diabetic Retinopathy

In most patients, an ophthalmologist can diagnose diabetic retinopathy during a routine eye examination.

In certain patients, more information might be obtained by a fluorescein angiogram. This test confirms the presence of retinopathy and helps to determine the areas that need laser treatment. During the test, dye is injected into a vein in the patient's arm. The dye circulates throughout the bloodstream and into the eye where it can be photographed.

Treatment for Diabetic Retinopathy

The only proven treatment for nonproliferative diabetic retinopathy is laser photocoagulation. This is indicated when the patient has clinically significant macular edema. Laser treatment has also been proven to preserve vision in patients with proliferative diabetic retinopathy. Vitrectomy surgery is also a proven form of treatment for severe/persistent diabetic vitreous hemorrhage or diabetic retinopathy-related traction distortion or detachment of the retina.

The only proven noninvasive treatment for nonproliferative diabetic retinopathy with macular edema (macular swelling) is laser photocoagulation. A laser is a device that delivers a split-second burst of light.

Before the treatment begins, the patient is seated in front of the laser. After the eye is numbed by anesthetic drops, a contact lens is placed on the eye, and the laser beam is focused through it.

In some cases, the ophthalmologist will refer to the photographs from the fluorescein angiogram to identify areas to be treated. The laser beam is aimed at the leaking vessels, and the ophthalmologist triggers the laser by foot.

A burst of light is visible for a fraction of a second. When the laser's light is absorbed by blood and pigment in the back of the eye, it is converted to heat, which coagulates leaky blood vessels and forms laser marks in the retina.

Studies sponsored by the National Eye Institute and performed at institutions around the country, including Wills Eye, have proven that photocoagulation is beneficial in eyes with nonproliferative diabetic retinopathy and macular edema and that it decreases the risk of moderate vision loss by almost two-thirds.

Laser photocoagulation is not appropriate for everyone with leaking vessels, and researchers continue to look for new and better ways to treat persons with nonproliferative diabetic retinopathy.

Laser for Proliferative Diabetic Retinopathy (PDR)

Laser is also helpful for proliferative retinopathy, in which new blood vessels (neovascularizations) grow on the surface of the retina. These neovascularizations can break and bleed into the vitreous, leading to serious vision problems, such as retinal detachments. Laser treatment for proliferative diabetic retinopathy can reduce blood vessel growth and decrease the risk of retinal detachment by helping to bind the retina to the back of the eye.

Vitrectomy in Diabetic Retinopathy

When a vitreous hemorrhage is dense enough to cause significant blurring, a vitrectomy might be necessary. In this surgical procedure, surgeons use a high-powered microscope to see inside the eye and to insert small instruments that will remove both the vitreous and the hemorrhage. The vitreous is replaced with a clear water solution.

After the surgery, some patients will notice a significant improvement in vision afterward. However, in about 20 percent of cases, patients may develop another hemorrhage. Because of this and the possibility of other complications, the ophthalmologist might recommend waiting for up to three months for the hemorrhage to clear before proceeding with another vitrectomy.

If the retina becomes detached, however, a prompt vitrectomy might be necessary in an attempt to remove retinal scar tissue and to preserve vision.

Prevention of Diabetic Retinopathy

Having regular, comprehensive eye examinations by an ophthalmologist is the best protection against the progression of diabetic retinopathy. It is recommended that all diabetic patients be examined at least once a year.

Patients with more advanced retinopathy might need more frequent monitoring. Patients who notice a blurring of their vision should report this to their ophthalmologist immediately.

In addition to regular eye exams, the most important aspect of prevention of diabetic vision loss is good control of blood sugar. The Diabetes Complication Control Trial demonstrated for patients on insulin therapy that "tight control" which is defined as finger-stick glucose checks three to four times daily with insulin adjustments, can reduce the rate of progression of diabetic retinopathy by up to 76% .