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

200 / THE BIG PROBLEMS FOR AGING EYES

have popularized the notion that sunlight and its associated ultraviolet rays can increase someone’s risk of developing cataracts. Several epidemiological studies appear to support this claim; in particular, a study from the Johns Hopkins Hospital in the 1980s found that watermen on the Chesapeake Bay, who, by reason of their occupation, had increased exposure to the ultraviolet-B (UV-B) radiation in sunlight, were found to have over a threefold risk of developing cortical cataracts compared with those with much lower exposure. The exact role of sunlight and UV rays in lens changes and cataract development needs further study. However, because there’s good evidence that the two are indeed linked, we recommend sunglasses for all our patients—especially those at risk for cataract development (including people with diabetes as well as people on certain medications that make them more sensitive to the effects of light exposure).

Although most sunglasses provide adequate protection from UV radiation, you should look for labeling claiming “100 percent UV-A and UV-B filtering.” The color of the sunglasses has little effect on their ability to protect your eyes. The tint should simply tone down the sun’s brightness to a level that’s comfortable for you. (The embedded chromophores in the lens that provide UV protection have little effect on the color or darkness of the sunglass.) Very dark gray lenses can decrease contrast, but gray is an acceptable color at lighter shades, as well. Amber and brown lenses are popular because people find that they alter natural colors minimally.

CATARACTS / 201

Green lenses, on the other hand, cause the most color distortion. Yellow lenses have been touted on midnight television commercials as great improvers of vision, especially outdoors. There is little scientific support for these claims, but hunters and other people who spend a lot of time outdoors have found them particularly comfortable. Polarized lenses have little effect on ultraviolet light, but they do cut glare substantially. Glare is a frequent complaint before and after cataract surgery, and polarized lenses may provide considerable comfort, especially for people who are exposed to a lot of reflected light (fishermen, boaters, and those who spend a lot of time driving on highways). Mirrored lenses, on the other hand, are purely cosmetic (especially if your goal is to look like a state trooper), have no true protective or comfort value, and may reflect unwanted UV rays onto the surrounding skin, causing sunburn.

Visual Impairment, and Paradoxical Improvement, from Cataracts

Like the lens in a camera that focuses light rays onto the film inside, the lens in the eye focuses light rays onto the retina. As cataracts develop over time, the lens becomes cloudy or hazy, allowing less light to reach the retina. The rays that do penetrate the lens can become distorted and scattered, accounting for such symptoms as blurred vision and halos around lights at night. Eventually this dimming of the lens reaches the point where stronger eyeglasses can no longer improve vision. This is

202 / THE BIG PROBLEMS FOR AGING EYES

because cataracts are not a refractive problem (one that can be corrected simply by changing your prescription). Rather, cataracts are a problem inside the eye. The lens becomes cloudy, like a dirty window. No matter what kind of glasses you put up outside the eye, they can’t focus light rays adequately through this hazy or dirty cataract window inside the eye. For your vision to get any better, the window will eventually need to be cleaned— or, as in the case of cataracts, removed.

One of the earliest signs of cataract development is called second sight. It’s an amazing phenomenon. Some people actually stop needing their glasses as they get older (see chapter 2). Even though they may once have needed glasses for distance, now they can see just fine without them. Others who were always dependent on reading glasses may slowly discover that they read just as well without any glasses. So how, you may be wondering, if a cataract is a clouding of the lens in the eye, can this cause better vision? The answer is that in its earliest stages, the clouding is minimal and has little effect on decreasing light and distorting vision. But at this early stage, as the cataract begins to form, the change in the consistency of the lens can have an effect on someone’s eyeglass prescription. These changes can alter the focus of light rays by the lens, so that people who were farsighted may gradually become nearsighted, and vice versa (though more often the former). This tendency toward nearsightedness as a cataract develops is called a myopic shift. Myopic shifts can have many other causes, such as certain medications (sulfa antibiotics, miotic eye

CATARACTS / 203

drops), systemic disorders (diabetes), and other ocular conditions (ciliary muscle spasm). Nevertheless, people with large changes in their eyeglass prescription over one or two years, especially if there’s a big difference between the two eyes, should be checked for cataract development. This change is occasionally the first clue that a cataract is developing despite only minimal changes in the lens visible during an examination.

Can Cataracts Be Prevented?

Vitamins

As we discussed above, age is the big cause of most cataracts—and as we all know only too well, there’s not much we can do to stop or turn back the clock. However, it has been suggested by several investigators that nutrition plays a role in cataract development, and changes in nutrition and vitamin supplementation have been tried to slow cataract development. Specifically, antioxidants such as riboflavin, vitamins C and E, and carotenoids, as well as niacin, thiamine, and iron, may alter cataract development.

The effect of nutrition, specifically antioxidants, on cataract development is currently being investigated by the National Institutes of Health (NIH) in a large clinical trial. This study, known as the Age-Related Eye Disease Study (AREDS), has enrolled some forty-five hundred people nationwide with various stages of cataracts and macular degeneration. These people have been randomly assigned to groups. Some groups take vitamin

204 / THE BIG PROBLEMS FOR AGING EYES

supplements containing copper, zinc, and an assortment of antioxidants, and other groups take placebos. Study participants will be carefully followed for ten years to determine the effects of dietary supplementation on these age-related eye conditions. Because nobody knows if these vitamins will have any effect at all—the only suggestions that they might help have come from a limited number of studies—at present we urge you to use caution here. Don’t rush right out and raid the health-food store. Vitamins aren’t candy, and you may risk your health if you take high-powered nutritional supplements without medical supervision. If you want to take something, a multivitamin with zinc, copper, and antioxidants can’t hurt.

Sunglasses

It has also been suggested, as discussed above, that wearing sunglasses with UV filters may slow cataract development. Ultraviolet rays penetrate the cornea and are absorbed by the human lens; laboratory animal and epidemiological studies suggest that exposure to sunlight and ultraviolet light may have an effect on cataract development. But whether (and how much) ordinary exposure to sunlight accelerates cataract development is uncertain. If you decide to use sunglasses—and this is probably a good idea—to cut down on light exposure when you’re outside, you should purchase the darkesttinted lenses you can tolerate, and look for UV coating that specifies that it blocks wavelengths below 400 nanometers.

CATARACTS / 205

Medications

Various medications, including aspirin, have been studied for their effect on cataract development. Aspirin appears to have a minimal effect, if any, on inhibiting cataract lens changes. However, there are several medications that have been specifically designed and marketed as “anticataract drugs.” These are much more popular outside the United States and include catalin, phacolysin (Lutrax, Quinax), bendazac, and phaka. However, spend the money at your own risk. The usefulness of these drugs in retarding or reversing cataract development is not widely accepted, especially in light of today’s excellent surgical results. That is, cataract surgery usually has such a good outcome that using unproven drug remedies seems not the best approach.

What Are My Treatment Options?

At first, the best treatment is education: having a good understanding of this problem and its effect on vision, and getting the most accurate eyeglass prescription possible, can help you cope with the often annoying consequences of cataract development. Improving the lighting at home with more and brighter lights (halogen lights, or 100-watt to 150-watt incandescent bulbs), positioning reading lamps over your shoulder for maximum illumination of the printed page, wearing sunglasses on bright sunny days to reduce glare, and limiting

CATARACTS / 207

the degree of vision you consider necessary for a normal life. Surgical removal of cataract lenses is considered when people find that the visual impairment has progressed to the point where their normal activities are curtailed and stronger glasses aren’t an option. An older person who doesn’t move around very much has fewer visual needs and can better tolerate a more advanced cataract than can a more active person, who may not be able to tolerate even an early cataract.

So, how active are you? This is an important question. And in answering it, by the way, don’t sell yourself short—or let your doctor or well-meaning relatives talk you out of surgery—with a rationale such as “Well, I’m in my seventies, I guess I should slow down anyway.” Poppycock! It’s your life, and the decision to undergo cataract surgery is an individual one; there are no strict rules to be applied here. There’s also no age cutoff. Is the visual impairment interfering with your job, special interest, or hobby? Is it affecting your level of independence, as driving becomes a problem or you become afraid to leave the house because of trouble seeing?

Cataract surgery may also be performed for other reasons besides improving your vision. A dense cataract will obscure an eye doctor’s view of the retina. This will make it difficult to follow conditions in the back of the eye such as glaucoma, diabetic retinopathy, and macular degeneration. Laser treatment of the retina is also difficult when there is a dense cataract. Very mature cataracts can lead to glaucoma or inflammation in the eye and should probably be removed.

208 / THE BIG PROBLEMS FOR AGING EYES

Consideration must also be given to what you expect to achieve with the surgery. In most instances, cataract surgery is done to improve vision; in other words, you expect that after the surgery, your vision will be better than it was before, whether you need to wear glasses or not. You should not undergo cataract surgery with the idea that you won’t need to wear glasses anymore. (Or because you hope cataract surgery will improve your golf game. It’s the old story: “Doctor, will I be able to play the piano after the operation?”“Yes,” replies the doctor. “Great! I never knew how to play it before.”)

When Should Surgery Be Performed?

When surgery should be performed is another difficult question. Visual acuity, as measured with eye charts, varies from office to office and from one tester to another. The most common acuity measurements used today in the United States are the familiar “Snellen acuity” measurements of 20/20, 20/40, and so on. In general, someone whose visual acuity cannot be brought to better than 20/50 with eyeglasses should consider surgery. This visual impairment must also be judged to be consistent with the degree of cataract observed clinically and the health of the eye. Also, a careful eye examination must be performed to make sure that this visual impairment isn’t due to other problems, such as corneal or retinal disease. Fortunately, modern microsurgical techniques make it no longer necessary to wait until cataracts are “ripe” before they can be removed.

When discussing such concepts as visual acuity and