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

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crafting your glasses should be watching the quality, not the clock.)

If I wear my glasses all the time, will I become dependent on them?

No. Remember, your eyes are in a constant state of flux your whole life (see chapter 2). No matter what you do, you can’t stop this process; your eyes are going to change anyway, with or without corrective lenses. All eyeglasses do is help us see better through these various unavoidable vision changes.

If you’re just starting to need a reading prescription or bifocals and you try to put off getting eyeglasses “so that your eyes won’t weaken further,” you won’t be doing yourself any favors—and you certainly won’t be toughening up your eyes by straining them, as if they were stomach muscles you could whip into shape if only you did enough sit-ups. Instead, you’ll find yourself putting up unnecessarily with blurred vision and headaches. As we age, our reading vision, in particular, falters; this trend increases with each passing year. So even if you don’t wear your eyeglasses, your reading vision isn’t going to get any better, and anyway, you’ll still have more of a “dependency” on eyeglasses in the future. Everybody does. Why should you be blurry and uncomfortable in the meantime?

Conversely, if you don’t wear your eyeglasses, your vision won’t necessarily get worse because of eyestrain. After about the first ten years of life, the critical years for the development of our vision, not wearing your eye-

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glasses has no effect on the outcome of your prescription. (During those first ten years, however, it’s very important to provide the retina with the best possible image for vision development, and wearing eyeglasses, if they are needed, is an absolute must.)

There’s nothing wrong with being clear and comfortable; you’re not giving in to weakness by seeing better. If it means wearing some form of corrective lens to achieve better vision, don’t feel that you’re harming yourself in doing so.

What does my prescription mean?

Your prescription is written in units called diopters. A “one-diopter lens” focuses light at one meter, or approximately forty inches. The diopter designation on your prescription does not indicate what your visual acuity is. (For more on this, see chapter 3.) If, for example, you have a prescription for one diopter of nearsightedness, then you really don’t see very well past the length of your arm; but the one-diopter designation doesn’t indicate what your vision is without your eyeglasses. Eyeglass prescriptions change by a quarter of a diopter at a time. On average, your vision changes one line on the eye chart for every quarter-diopter of prescription that you need. For someone with one diopter of nearsightedness, vision without eyeglasses is generally about four lines higher on an eye chart than the 20/20 line, or 20/50 vision.

Your prescription will sometimes include a designation for axis. The axis is the specific direction in which the correction for astigmatism is placed. Because astig-

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matism is an optical distortion that is caused by the eye having more curvature in one direction than in the other (see chapter 2), corrections for astigmatism always have a particular orientation.

If you are someone who needs to wear a bifocal, then your prescription will have a designation for add (see chapter 2). Your distance prescription will allow your eyes to focus appropriately on objects that are usually twenty feet away and beyond. The “add” describes the amount of reading correction that is added to the distance prescription in order to allow your eyes to focus at a reading (or near-working) distance.

How should I clean my new lenses?

Always begin by rinsing your lenses thoroughly with tap water. (Between cleanings, dust and debris settle on the lenses. Rubbing a lens with a cloth—your shirttail, for instance—actually grinds the dust and debris into the surface of the lens, creating fine scratches.)

After rinsing, spray them with a cleaner designed especially for eyeglass lenses—window cleaners often contain ammonia, which can damage lens coatings—or apply a small drop of a mild liquid dish detergent to each lens. Gently rub the cleaner into the lens with your thumb and forefinger and then rinse thoroughly with hot water. Hot water evaporates from the lens surface faster than cold water, making it easier to dry the lens. Finally, always use a soft paper towel or lint-free tissue to dry your glasses. Tissues with skin softeners and per-

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fumes may smudge your freshly washed lenses, and cloth towels can scratch.

What is a “no-line” bifocal?

Actually, it’s a little more complicated than it sounds. As discussed in this chapter, a bifocal is an eyeglass that does two jobs: the top part corrects your distance vision, and the bottom is used for reading. Traditionally, these two portions have been separated by a distinct line.

“No-line” bifocals come in two basic varieties. In the first, called a blended bifocal, the line is blended out, leaving a thin blurred zone between the distanceand nearlens portions. In the second and more popular kind, called a progressive no-line bifocal, there’s a gradual progression between the distance and near prescriptions. The big advantage here is that instead of the wasted blurry space, there’s a bonus zone for intermediate vision (“arm’s-length” vision, such as the distance between you and a computer screen or a shelf at the grocery store).

I just bought new glasses. Can I still get some use out of my old pair?

Sure. People do it all the time. Most of our patients keep at least one old pair of eyeglasses around the house as a spare, or to wear when doing yard work or any other potentially lens-scratching activity. Some people have their old eyeglasses darkened with a tint by an optician and made into prescription sunglasses. There are many ways to give new life to an old frame. One of the best is

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to donate them to a “recycling” agency so that someone else can use them (see below).

Can I recycle my old eyeglasses?

Absolutely—and someone will bless you for it! Eyeglasses, both frames and lenses, are processed at regional centers, categorized by their lens prescription and style, then sent to underprivileged areas in the United States and to underdeveloped countries and dispensed to those in need. Ask your eye doctor, local hospital, or community organizations (in our area, the Lions Club has been particularly involved with this recycling project).

Can I do anything to alleviate computer-related eye problems?

If your long hours in front of the computer are hurting your eyes, you’re certainly not alone. An estimated sixty-six million people in this country have computerrelated vision problems: eyestrain, irritated eyes, blurred vision, even headaches.

But there are some things you can do. The easiest and most low-tech solution is simply to give those accommodation muscles (see chapter 2) a break every so often by looking across the room or out the window. Administering teardrops several times a day may help. Progressive or “no-line” bifocals, or “computer lenses” (with an intermediate-distance prescription), may help ease the strain on your eyes. You might also ask your eye doctor about getting antireflective coatings or tints on your eyeglasses; these can break up the reflection of overhead

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lights and improve contrast of the screen. Also, many computer stores sell glare-cutting filters that sit over your screen or monitor. (Speaking of glare, if your computer sits directly in front of a bright window, you’ll notice a big improvement if you either move it or keep the curtains drawn.) Finally, positioning your monitor slightly below eye level makes it easier for your eyes to converge (see chapter 2) on the screen.

My daughter sits too close to the television and my husband stares at his computer screen for hours. Will this damage their eyes?

This falls under the “reading in dim light” category of eye worries, and fortunately the answer is the same: no. No research has ever proven that TV screens or computer monitors harm the eye. However, watching any kind of screen, TV or computer, from the same vantage point for prolonged periods can cause eye fatigue and discomfort. (For tips on alleviating computer eyestrain, see the previous question.) As with any prolonged activity involving the eyes, take frequent breaks; look around the room every fifteen to thirty minutes, to give your accommodation muscles a rest. Also, to avoid dry eyes, remember to blink frequently, and use supplemental teardrops if needed. (For more on these, see chapter 13.)

What about those “dime-store” reading glasses? Are they any good?

Over-the-counter, or “dime-store,” reading glasses are sold in many drug stores and grocery stores as well as in

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specialty stores. These glasses come in varying strengths and are usually labeled with the same power system as prescribed reading glasses. Because they are inexpensive, many people who enjoy using them will purchase multiple pairs so that they can leave one at work, one by their favorite reading chair, and one on their nightstand, and never have to worry about where they left their glasses.

Dime-store reading glasses can be an excellent alternative for someone with presbyopia who has little or no need for a distance prescription, or for someone who requires an additional reading prescription while wearing contact lenses. However, because both lenses in these types of glasses have the same effective power, they might not work well if one of your eyes needs a significantly different prescription from the other.

Additionally, these types of glasses are set up with optical centers that provide for an average pupillary distance, one that won’t necessarily match your eyes. If you experience headaches, discomfort, print that swims or moves while you read, or double vision with your over- the-counter readers, then the optical centers are probably off with respect to your eyes.

Even if you do get symptoms from wearing these glasses due to inappropriate power or pupillary distance, they will not harm your eyes. The symptoms will almost certainly go away when you stop wearing the glasses.

5

Contact Lenses: Everything You Need to Know

For some people, glasses are a plain old nuisance. They slip down on your nose, get smudged—or worse, misplaced (for folks who rely on more than one pair of glasses, this seems to happen several times a day!).

Thank goodness, then, for contact lenses. For the millions of people who wear them, contacts are the lenses of choice for several reasons. Many find contacts to be much simpler than glasses; once they’re in for the day, it’s easy to forget about them (except for adding the occasional rewetting drop). Also, they provide much better peripheral vision than glasses. Is this important? Absolutely. Better peripheral vision can help keep your eyes more relaxed when you’re reading and focusing—and this, in turn, helps reduce fatigue and eyestrain. For sports and recreational activities, better peripheral vision can even boost your performance.

Also, a contact lens moves with your eye, so you’re always looking through the center of the lens, the part of

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the lens that provides the best vision. In contrast, when you’re wearing glasses and you glance to the side, sometimes your vision seems distorted. (This is because, due to the nature of many eyeglasses, the lens doesn’t provide the same quality at its edges as it does in the center.)

If your prescription is strong, your glasses will actually change your perception of the size or relative distance of whatever you’re seeing. Once you get used to your glasses, of course, you tend not to notice these things. But contacts give the world a more natural appearance. Putting the lens correction on the eye itself minimizes these size differences and often provides better visual acuity, which means you can read smaller letters on the eye chart. (For more on visual acuity, see chapter 3.)

Still, despite these and other advantages, contact lenses aren’t ideal for everybody. Are they for you? This chapter may help you decide.

How Contacts Came About: From

Leonardo to Today

The notion of putting a corrective lens on the eye to achieve better vision is certainly nothing new. In fact, Leonardo da Vinci came up with this brilliant idea some 450 years ago. (Although no lenses were manufactured at that time, detailed drawings and descriptions were made.) A. E. Fick, a scientist in Zurich, manufactured the first contact lens in 1887 but soon found out that the human eye didn’t like wearing lenses made of actual

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glass. It took a major innovation, in the 1940s, to produce the ancestors of the contact lenses we wear today: plastics. Those original lenses were made of a material called PMMA, which in fact was so well tolerated by the human eye that it’s still used for hard contact lenses, for intraocular lens implants, and for orthopedic purposes.

Soft contact lenses didn’t become available in this country until 1972, when Bausch and Lomb first introduced them to the American market. The original soft lenses tended to be more comfortable than the hard lenses available at the time, but because they were limited to just a few sizes, these lenses didn’t fit many people. The big difference between hard and soft contact lenses was that the new soft lenses allowed oxygen to pass through them—not just around the lens, as with hard contacts. This made for a much healthier lens environment, because it enabled the eye to “breathe” with a lens in place. Lack of oxygen to the cornea can lead to decreased vision from corneal swelling and epithelial cell damage.

Since 1972, contact lenses have changed and improved considerably. Now, lenses are designed to correct almost any vision problem and are available in special designs for extended wear, cosmetic changes (like eye color), and disposability.