Ординатура / Офтальмология / Английские материалы / The Eye Book A Complete Guide to Eye Disorders and Health_Cassel, Billig, Randall_2001

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These membranes, which often bleed and grow fibrous tissue, can cause severe scarring of the macula—and, thus, visual impairment. This central macular disfiguration is often referred to as a disciform scar.

Who’s at Risk?

ARMD affects an estimated 3.5 million older Americans. (One Massachusetts study, the Framingham Eye Study, conducted on a group of predominantly Caucasian individuals, estimated that age-related macular degeneration affected about 6 percent of adults between ages sixty-four and seventy-four, and nearly 20 percent of those over age seventy-four. Other studies have suggested that the incidence is 10 percent and 30 percent, respectively.) The National Eye Institute of the National Institutes of Health blames ARMD (mostly the wet form) for more than sixteen thousand new cases of legal blindness each year. ARMD is considered the major cause of severe vision loss in older adults in the United States and other countries including Canada, England, and Australia. Unlike cataracts, which cause a reversible form of vision loss, age-related macular degeneration’s damage is irreversible. Even glaucoma and diabetic retinopathy, two other well-known causes of serious vision problems in people over age fifty, are much more treatable.

Who’s at risk? Well, despite several studies attempting to identify predisposing factors, there’s not much enlightenment in this area. The most obvious risk factor re-

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mains age. We do know a few generalities. The disease is more common in women than men. Heredity also seems to be a risk factor; if you have a family history of age-re- lated macular degeneration, you should have a careful eye examination done by a specialist familiar with the diagnosis and treatment of this disorder. People with blue eyes, especially Caucasians, seem more susceptible.

Other risk factors linked to ARMD—but definitely not proven to cause it—include cigarette smoking, cardiovascular disease, and high blood pressure. Lifetime exposure to sunlight may also be a factor, some studies have suggested. People may become more susceptible directly, through the sun’s damage to retinal cells, or indirectly, through an inability of the retinal cells to repair themselves after sunlight-caused damage. (Just as the sun damages unprotected skin, it can also damage unprotected eyes.) Although in theory sunglasses may modify sunlight’s effect on the retina, no definitive, long-term studies have been conducted to prove this.

The role of vitamins and minerals has also been a subject of scientific controversy. Theoretically these may also protect the retina against sun damage. Studies in animals and humans have suggested that there may be an association between retinal phototoxicity (cell damage caused by light) and levels of such vitamins as A, E, and C.

Because the wet form of ARMD can result in such devastating vision loss, scientists have tried to identify specific risk factors associated with its development. One thing they’ve found is that the type and extent of drusen and retinal pigment epithelial changes can help predict

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the development of subretinal neovascular membranes. Large, soft drusen—especially when found in both eyes and accompanied by significant epithelial changes— raise someone’s odds of developing these membranes. People who already have a subretinal neovascular membrane in one eye are also more likely to develop one in the other eye.

Prevention: Can Nutrition Make

a Difference?

As to prevention—again, much speculation, little concrete information. Most studies on the treatment of subretinal neovascular membranes have served mainly to emphasize our limitations and inability to control this devastating process. This has led many to search for new treatment pathways, and to seek preventive measures.

One of these new avenues of study is nutrition—a long-neglected area of research. Frankly, aside from what our mothers always told us about the benefits of eating carrots, we don’t know much about the preventive effects of vitamin supplements on such problems as macular degeneration and cataracts. On the other hand, we do know a fair amount about the effects of vitamin deficiencies on vision and eye health. From animal studies we’ve learned that dietary deficiencies in vitamins A and E can cause the retina to degenerate. Other studies, in rats, have suggested that vitamin C may have a protective effect against sun damage to retinas. How does this information relate to the onset of age-related macular

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degeneration? We don’t know. The Baltimore Longitudinal Study of Aging, the Eye Disease Case Control Study, the Beaver Dam Eye Study, and other human studies have suggested—but not proven—a link between age-related macular degeneration and such antioxidants as vitamin E, vitamin C, and betacarotene.

Another clinical trial, investigating the effect of oral zinc supplements on the progression of ARMD, has suggested a beneficial effect. The Age-Related Eye Disease Study, conducted by the National Eye Institute, is a large, multicentered clinical trial designed to probe these suggested links between diet supplements and such eye diseases as cataracts and ARMD in forty-five hundred older Americans, who will receive either nutrient supplements or a placebo. (Neither the investigators heading the study nor the patients will know who’s getting what.) The supplements contain concentrations of antioxidants and trace metals. Participants will be examined regularly, at least twice a year, for ten years. The results of this study should give us much better insight into the role of nutrition in eye disease.

Signs and Symptoms of ARMD

Age-related macular degeneration, like many other eye disorders, is at first a dangerously silent, stealthy process. By themselves, drusen and retinal pigment epithelial changes usually don’t affect vision. Even when drusen become large and pronounced, they rarely cause a noticeable problem; neither do pigment epithelial

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changes in the retina. However, central reading vision does become affected over time as these changes become more severe and involve the foveal region. For many people the first signs of trouble may be that when they’re reading or looking at straight edges, such as table tops or patterns on clothing, the lines look crooked or wavy; this is usually more pronounced in one eye than the other. Later, reading becomes particularly difficult as letters and words become distorted. Other people notice that their eyes have trouble adjusting from bright sunshine to a dimly lit room; people with advanced age-related macular degeneration often need a few minutes to adapt to this change in lighting.

The Importance of Early Detection and

Regular Monitoring

If you’ve been diagnosed with age-related macular degeneration, it’s essential that your vision be monitored regularly. Your eye examinations should include a careful dilated retinal evaluation by an ophthalmologist who is very familiar with this disorder and its clinical stages. If you’re considered to be at high risk for developing subretinal neovascular membranes, you may need eye examinations as often as every three to four months. If your retinal changes are less advanced, you may need to be examined only every four to six months.

Many eye doctors advocate home tests of visual acuity and function as a do-it-yourself means of monitoring macular degeneration’s progression. The most pop-

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ular means of doing this is called the Amsler grid (see figure 9.4B). As described in chapter 3, this is a black-and- white grid, observed at a distance of about fourteen inches with your normal reading glasses or bifocals (see figure 3.4). You should test each eye separately and as often as every day if you’re a person at high risk for wet ARMD. Be sure to report anything unusual to your eye doctor immediately; this includes a loss of clarity, distortion, or waviness of the lines. Any changes may indicate a progression in macular degeneration—most important, the development of subretinal neovascular membranes; and these, if detected early enough, may be amenable to treatment.

Why is early detection important, if macular degeneration isn’t usually treatable? A good question. Although there is no treatment for the dry form of ARMD, lasers can sometimes be used successfully to treat the new membranes that develop in the wet form. And if this is the case for you, early detection and treatment may mean the difference between useful sight and legal blindness.

For patients with age-related macular degeneration, a basic eye exam is often inadequate to establish whether these membranes are present underneath the retina. In patients in whom these membranes are suspected— from the patient’s history, for instance, or because of retinal changes—imaging techniques including fundus photography and a fluorescein angiogram can help detect their often elusive presence. The fluorescein angiogram (see chapter 3), an essential tool in evaluation and treatment, helps us distinguish between normal and abnor-

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mal blood vessels in the retina. Since these new blood vessels develop below the retinal pigment epithelium— which means we can’t see them with the naked eye—the fluorescein dye study helps reveal their location and extent, especially for laser treatment. It’s also used after laser treatment, to make sure that the membrane has been successfully treated, and to monitor patients closely after treatment, to spot the earliest sign that the problem is recurring (see below).

Other monitoring techniques have been investigated over the years but have proven less successful than fluorescein angiography. One promising new technique, however, may be computer-enhanced indocyanine green angiography, which uses video imaging to study blood flow in the choroid and retina.

Treating ARMD

This is a short section, because the vast majority of eyes with macular degeneration, dry or wet, can’t be helped by any form of treatment. In fact, there are currently no treatments available for the dry form, the one that affects most people with macular degeneration.

Lasers

Although laser treatment has been shown to be successful for patients with the wet form of macular degeneration (the subretinal neovascular membranes), few people—an estimated one out of every ten—are diag-

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nosed soon enough or considered good candidates for the procedure.

Much of our information on the natural history and treatment of subretinal neovascular membranes comes from the Macular Photocoagulation Study, a large clinical trial conducted by the National Eye Institute. In this study, argon lasers, in a procedure called argon laser photocoagulation treatment, were used on membranes of various sizes and locations in the macula. Investigators in the study found that 60 percent of the patients with well-de- fined subretinal neovascular membranes close to but not involving the foveal region of the macula developed severe visual impairment within three to five years. As might be expected, this percentage increased in patients with subretinal neovascular membranes directly underneath the fovea.

Laser treatment has been shown to be effective for some, but not all, patients with subretinal neovascular membranes. In the study, people with well-defined subretinal neovascular membranes outside the foveal region did better—in other words, they had less severe vision loss—with laser treatment than people who received no treatment. Note: Some people who received laser treatment still lost their vision, sometimes because of the laser treatment itself. Also, the laser treatment didn’t always prevent vision from deteriorating further. Thus, in this study, laser treatment merely reduced someone’s odds of severe vision loss. It didn’t eliminate the risk entirely, but it did seem to help many of the people who received it.

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Another fact of the laser treatment is that, even in the best cases, it destroys retinal tissue. For a surgeon to do a good job attacking the subretinal neovascular membrane, it’s inevitable that some of the healthy retina will be lost as well. And often this results in a permanent visual blind spot. (The size and location of this blind spot depend on the position and extent of the subretinal neovascular membrane.) Another frustrating fact of laser treatment is that the membranes often grow back. The recurrence rate has been estimated to be as high as 42 percent within the first year, and as high as 53 percent within the second year. So if you’re considering laser treatment, make sure you discuss the risks—and exactly what you stand to gain and lose—thoroughly with your surgeon. For some people this treatment can be more devastating than the disease.

Surgery

At this time surgical approaches to age-related macular degeneration are purely investigational—and controversial. Retinal specialists attempting to treat subretinal neovascular membranes surgically haven’t met with much success. Retinal transplants have also been tried by many, but so far we’ve been stymied by two basic problems. One of them is rejection: the eye—which does very well with corneal transplants, because they don’t involve many blood vessels—tends not to accept someone else’s retina without a fight. The other problem is with retinal cell regeneration and differentiation: the cells don’t work

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as they should after they are replaced in the eye. And fi- nally, the ultimate functional practicality of retinal transplants remains questionable, since transplanted cells must also be able to reestablish and maintain the many complex nerve connections to the brain. Computer microchips implanted on the retinal surface are also being investigated as a way of restoring vision in people with severe forms of macular degeneration.

But many people have high hopes for the future of surgical treatment of macular degeneration. Many scientists remain optimistic about the potential of retinal transplants—one day—to restore vision in people with severe macular degeneration.

Other Treatments

Another exciting area of research in macular degener- ation—at least in the wet form of it—centers around medical treatments. Can drugs help quell the recurrence of new vessel membranes after laser treatment? Or better yet, can they block their growth in the first place? Thalidomide may somehow inhibit the growth of subretinal neovascular membranes, and scientists are currently studying the use of this drug in treatment. Other treatments under investigation include dye-assisted photocoagulation and radiation therapy. These techniques may enhance doctors’ ability to more accurately and precisely treat subretinal neovascular membranes.

There’s no good way to measure age-related macular degeneration’s true impact—its threat to patients’ inde-