Diabetic Eye Disease
The most common diabetic eye disease is diabetic retinopathy, the leading cause of blindness in American adults. Diabetic Retinopathy (reh-tin-AH-puh-thee) is an eye condition that affects the retina in some patients who have had diabetes for many years. The retina, which is the light-sensitive nerve tissue that lines the back of the eye, is vital for vision.
There are two forms of this condition: background retinopathy (the milder form) and proliferative retinopathy. Background retinopathy generally progresses slowly, over years, and eventually causes some visual disturbance; sometimes it develops into the more serious proliferative stage. The exact cause of the background retinopathy or why it progresses to proliferative retinopathy is not known. However, it is related to the length of time you have had diabetes, and it is more common in insulin dependent diabetes than in cases where the diabetes can be controlled with an appropriate diet or oral medications.
Since there are usually no early warning symptoms, patients who have diabetes need to have a complete eye examination regularly, at least once a year.
What Happens in Background Retinopathy?
The earliest changes are subtle and only slightly different from normal. Some of the retinal blood vessels gradually enlarge; some become irregular in size and develop some tiny weak spots (microaneurysms), which is the hallmark of this condition. They begin to leak exudates (fluid, fat, and protein) and blood.
At first, vision may be normal or only slightly affected depending on where the leaks are located. The condition varies over time, sometimes getting better for a while and then worse, but tending to slowly worsen. As it advances, some of the small retinal blood vessels gradually become obstructed, resulting in a patchy loss of retinal nourishment. In some patients this leads to the development of proliferative retinopathy.
What Happens in Proliferative Retinopathy?
New, abnormal blood vessels begin to grow (proliferate) over the surface of the retina and optic nerve, the “telephone wire” that transmits images from the eye to the brain. (Doctors feel that they form in an attempt to nourish the patches of “starving” retina.) Unfortunately, these blood vessels are usually fragile, and frequently break and bleed.
If they bleed into the vitreous (into the center of the eyeball), vision can become clouded from the blood. At first the blood is rapidly absorbed, so vision tends to clear in a few weeks. But eventually, with rebleeding, vision may not clear so rapidly or even at all.
As more new vessels grow, the risk for more bleeding increases. Scars form and may tug on or even tear the retina, which can lead to a retinal detachment. All of these developments have the potential for leading to blindness.
In its early stages, background retinopathy does not cause any symptoms. Later, it can produce blurring of vision (from retinal leakage and swelling) that glasses cannot help. The early stages of proliferative retinopathy may also produce no visual symptoms; but later, bleeding can cause a sudden appearance of floaters, blurring, or even almost total loss of vision. Neither type, on its own, is likely to cause pain. But the proliferative form is sometimes associated with other eye problems that can cause pain.
As part of the history taking, you will be asked some important questions, such as how long have you had diabetes?, how are you controlling it?, and how well it is being controlled?
A complete vision examination will be done with your pupils dilated (enlarged). An ophthalmoscope will be used to study the inside of your eyes. The pressure inside your eyes will be checked with a painless test call tonometry. Depending on the type of tonometer used, you may be given anesthetic eyedrops.
To help evaluate the progression of the condition, retinal photographs may be taken and a fluorescein angiogram may be done. Here, a greenish dye is injected into your arm vein, which helps identify the retinal abnormalities in the photographs.
For background retinopathy or even for minimal proliferative retinopathy, you may not need any treatment other than keeping your diabetes under good control. If the condition is more serious and is threatening your vision, laser treatment may be recommended. Laser beams may be used for “focal treatment” to stop discrete retinal leakages, or for PRP (panretinal photocoagulation) – to create hundreds of tiny burns in the retina that, by some unknown mechanism, seem to reduce retinal swelling and congestion and the number of dangerous, abnormally proliferating blood vessels, thus reducing the risk of internal bleeding. More than one series of laser treatments may be needed, but all can be done on an outpatient basis and are usually painless.
Laser treatment may not help severe cases and sometimes lasers cannot be used at all, such as when the abnormal blood vessels, scars, and blood are too dense to let the laser beam shine through the retina. Then, a major eye operation called vitrectomy may be suggested, to attempt removal of the scars and cloudy or bloody tissue. If this procedure is successful in clearing up the cloudy material inside the eyeball, laser treatment may then become possible.
Vision improvement does not always follow a vitrectomy, but when it does it can be dramatic. However, vitrectomy has a high risk of serious complications, including more bleeding, retinal tears and detachment, so it is used only for the most advanced cases of diabetic retinopathy that are otherwise untreatable.
Diabetic retinopathy is one of the major causes of defective vision and blindness in our country today. Although it is not totally preventable, its course may be made far less severe by diagnosing any eye problems early and then keeping a close watch for progression so that early treatment can be instituted when necessary. If you have diabetes, make sure you have a thorough eye exam at least every year (more frequently in advanced cases), and you should always take the best possible care and control of your diabetes.