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Penn State Ophthalmology

Diabetic Retinopathy

What is it?

Diabetic retinopathy is a complication of diabetes that damages the eye's retina and can result in blindness. The term "diabetic retinopathy" refers to changes in the retina which often occur in people with diabetes. These retinal changes may initially be symptomless, or they may eventually lead to blindness. Diabetic retinopathy is one of the major complications of diabetes, along with neuropathy and nephropathy. It is the leading cause of vision loss among working-age adults in the US and other industrialized countries.

Normal  vs. diabetic retina

Diabetic retinopathy can be divided into four stages: preclinical, nonproliferative, proliferative, and late proliferative. These four stages are described in more detail below.

A person with diabetic retinopathy may have serious retinal damage before noticing any changes in vision. Therefore, it is important for diabetics to have their eyes checked regularly by an eye doctor.

The cause of vision loss in diabetic retinopathy is not known. There are known ways for diabetic people to reduce their chance of developing diabetic retinopathy and to slow down progression of the disease. However, there is currently no treatment to prevent or reverse the condition. It is therefore critical for scientists to discover methods to treat diabetic individuals before irreversible vision loss occurs.

Who gets it?

Half of all Americans diagnosed with diabetes develop diabetic retinopathy. People with Type I (juvenile onset) and Type II (adult onset) diabetes are at risk. This condition usually doesn't develop, however, until around 10 years after the onset of diabetes. Diabetic retinopathy may also occur in pregnant women with diabetes. Most diabetic individuals--approximately 90%--will eventually develop some degree of retinopathy. The chances of developing diabetic retinopathy increase the longer a person has had diabetes and the more severe the case.

What causes it?

The retina is the light-sensitive membrane at the back of the eye. When light enters the eye, the cornea and lens near the front of the eye focus the light onto the retina. The central area of the retina, called the macula, contains hundreds of nerve endings packed closely together. These nerve endings are responsible for the sharpness of the visual image. The retina converts the image into electrical impulses that are carried to the brain by the optic nerve. So, without the retina, the eye cannot communicate with the brain and vision is lost. Diabetes affects the retina because high blood sugar levels damage the blood vessels that feed the retina by making them weak. The weakened blood vessels are more likely to cause macular edema, a condition in which the vessels leak fluids into the inner part of the eye. The blood vessels may also become deformed and blocked.

The main risk factors for developing diabetic retinopathy are:

• High levels of blood glucose--controlling blood glucose levels can significantly reduce a diabetic individual's chances of developing retinopathy
• Pregnancy
• Hypertension
• High serum lipids
• Diabetic kidney disease
• African-American or American Indian ancestry

What are the symptoms?

There are two types of diabetic retinopathy. 

• Nonproliferative retinopathy is a condition in which the small capillaries in the retina break and cause macular edema. The fluid makes the macula swell, causing blurred vision. 
• Proliferative retinopathy occurs when the damage to the retina causes new blood vessels to grow abnormally. These vessels also bleed easily into the inner part of the eye, causing blurred vision and dark spots that appear to float in your vision, and eventually destroying the retina. In extreme cases, you may only be able to tell light from dark in the affected eye. Heavy bleeding (hemorrhages) often occur during sleep. Proliferative retinopathy can lead to episodes of temporary blindness, or permanent blindness. Because damage to the blood vessels of the retina occurs over time, you may have diabetic retinopathy without any noticeable symptoms.

What happens in diabetic retinopathy?

The table below describes the physical and functional changes involved in the four stages of diabetic retinopathy:

How is it diagnosed?

Diabetic retinopathy is diagnosed through an eye examination. Your eye care specialist, or ophthalmologist, will put drops in your eyes to dilate, or widen, your pupil so he or she can get a closer view of the retina. The ophthalmologist will check your retina for early signs of the disease, which include leaking blood vessels; macular edema; pale, fatty deposits, called lipids on the retina, which signal leaking blood vessels; damaged optic nerve tissue; and any changes in the blood vessels in the eyes. An instrument called an ophthalmoscope magnifies the retina in greater detail. The ophthalmologist may also test how well you see at various distances. Your specialist may also measure the pressure in the eye, called tonometry, to check for signs of glaucoma, which also commonly occurs in people with diabetes. The extent of diabetic retinopathy is commonly determined through a test called fluorescein angiography. The ophthalmologist injects a special dye into a vein, waits for the dye to reach the retina, then takes photographs of the retina. The photographs show any leaking blood vessels.

What is the treatment?

The only way to delay the ocular complications of diabetes is to exercise the tightest possible control of blood glucose. Therefore, the primary treatment for diabetic retinopathy is intensive control of the diabetes. In addition, blood pressure and serum lipid levels should be kept normal, if possible.

There are two commonly used treatments for diabetic retinopathy. 

• Severe macular edema and proliferative retinopathy are treated with laser surgery, called laser photocoagulation. Laser photocoagulation is a painless treatment in which a laser beam is aimed through the eye to destroy any new blood vessels and seal off those that are leaking. During the treatment, you may see bright flashes of light. Your vision will remain blurred for a few hours after the procedure and you may feel some discomfort in the eyes. People with proliferative retinopathy may lose some side (peripheral) vision after this surgery. Laser surgery may also affect color and night vision. Laser surgery is not a cure. 
• People who have proliferative retinopathy are always at risk for new bleeding. If you have had extensive bleeding from damaged blood vessels, you may need an operation called a vitrectomy. The area of the eyeball closest to the retina is filled with a gel-like substance called the vitreous humor, which helps give the eyeball its shape. A vitrectomy is performed if you have a lot of blood in the vitreous. Vitrectomy is often done under local anesthesia. With this procedure, the doctor makes a small incision in the white part of the eye. A small instrument is used to remove the cloudy vitreous and replace it with a salt solution. Your eye will be red and sensitive right after the procedure so you will need to wear an eyepatch for a short time to protect it. Your doctor will also give you medicated eye drops to prevent infection. Vision gradually improves after the vitrectomy, and the vitreous humor is gradually replaced. Even people with advanced retinopathy have a 90 percent chance of keeping their vision if it is treated before the retina is severely damaged

Laser surgery (photocoagulation) is the standard and only proven treatment for established (stage 2 or 3) retinopathy and/or macular edema, and it may slow the progression of vision loss. However, this treatment is destructive to the peripheral retina and does not stop the progression of the disease. Laser surgery reduces by 90% the chances that a person with diabetes will become legally blind.

Photographs (sometimes with fluorescein angiography) are used to plan laser treatment.

Once the retinopathy advances to the proliferative phase, it is very difficult to reverse.

Current research

There are a few new treatment methods under consideration today but these are so far strictly experimental. The PSRRG is involved in some of these experimental approaches. One of the aims of the PSRRG is to develop novel treatments to prevent diabetic retinopathy before vision impairment sets in.

Possible causes of vision loss

The cause of vision loss in diabetic retinopathy is not known, but clearly relates to altered metabolic control. This is one of the areas of active interest in the PSRRG. One of the leading hypotheses is that either the lack of insulin action or increased sugar levels cause changes in the metabolism of the cells of the retina, and inhibit the normal interactions between neurons, glial cells and blood vessels that are necessary for normal vision.

Self-care tips

Blindness can be prevented in 90% of people with advanced diabetic retinopathy if the condition is treated before the retina is extremely damaged. That is why it is so important to have yearly eye exams if you have diabetes. If you have diabetic retinopathy, you may need to have your eyes examined, with the pupils dilated, even more frequently. Controlling your blood sugar levels by following your doctor's recommended treatment will also help slow down the progression of retinopathy and reduce the need for laser surgery. All pregnant women with diabetes should have dilated eye examinations during each trimester of their pregnancy to check for retinopathy.

This information has been designed as a comprehensive and quick reference guide written by our health care reviewers.  The health information written by our authors is intended to be a supplement to the care provided by your physician.  It is not intended nor implied to be a substitute for professional medical advice.