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

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problems that even a few years ago could be compensated for only by those thick, uncomfortable, Coke-bot- tle lenses.

So, faced with all these choices, what do you do now? If you’ve never before needed anything to help you to see better, how do you go about deciding what’s right for you? What factors are important in making this decision? First you’ll need to consider carefully your own needs, your lifestyle, job, and hobbies, and then weigh them against the general health of your eyes and the particular vision correction you require. Also, know that you certainly don’t have to decide things all by yourself; that’s where this book—and, of course, your own eye doctor and optician—can help. In this chapter we’ll discuss all of these options and, we hope, help you narrow down your choices and come to an appropriate decision.

How to Find What’s Best for You: Your Guide to Lenses and Frames

Eyeglasses are the most frequently used means of correcting vision. Until about twenty-five years ago they were strictly functional and, as anyone whose face has ever been dwarfed by huge black horn-rims can attest, not much of a fashion statement. Now, with literally thousands of frames and hundreds of lens designs available, the selection can be overwhelming.

What’s best for you? The physical attributes of your face may be one limiting factor; obviously, not all frames will look good on everyone. Your prescription may be

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another; a bifocal prescription or a very strong prescription might not fit well into a certain type of frame. A frame that doesn’t fit your face won’t do you much good, either; stylish but ill-fitting glasses won’t allow the prescription to align properly over your eyes, and as a result your vision won’t be clear or comfortable.

Ask for help. Your doctor and optician can guide you to the best selection of frame and lens design. Then, you and they can work together to make a decision. Discuss your concerns with your doctor at the time of your eye examination. Be sure to mention any specific visual needs—if you spend a lot of time reading, for instance, or using a computer—and ask what type of lens design would best suit those needs. Then, consult with your optician. Ask what type of frame is best suited for your face and the prescription. Lenses that provide the same function can be manufactured in numerous ways, some of them better for your needs than others.

First, the Lenses

Configurations

Eyeglasses are made in two basic configurations: single-vision and multifocal. As the names suggest, singlevision glasses have only one prescription, or lens power, whereas multifocals have more than one power within each lens. Traditionally, single-vision lenses were used by people who didn’t need more than one prescription— someone who needed eyeglasses only for driving, perhaps, or just for reading. Or maybe someone needed

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glasses for both activities but used the same lens power for both. Single-vision eyeglasses sometimes work better for specific activities, such as viewing a computer screen at a fixed distance.

Multifocals may be bifocals, trifocals, or progressive addition lenses. These lenses address more than one need and often allow people to perform various visual tasks wearing the same pair of eyeglasses.

Bifocals have two prescriptions within the same lens, one for distance and one for reading. Bifocals may have a line across the entire width of the lens, with the reading portion on the bottom, or they may contain the reading area within a small part of the lens. Today bifocals can be made without a noticeable line, thanks to a sophisticated polishing technique. These “blended” bifo- cals—not to be confused with progressive bifocals, discussed later—may look better cosmetically. However, there’s a drawback: the seamless line leaves a wide area of distortion where the two lens powers meet, and this shrinks the size of the available reading area. This blend is also noticeable—and, to some people, a nuisance— whenever you shift your gaze from distance viewing to near viewing. That is, although others see no line in your glasses and probably won’t realize that you’re wearing bifocals, you see a line, and it’s fairly wide.

Trifocals add a third lens for intermediate vision, for viewing distances of about two to three feet. The intermediate lens has to be positioned just below the pupil, so that the reading portion can still sit high enough in

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the lens for you to use it comfortably. Because the intermediate lens sits up so high, the line is much more noticeable than with a bifocal, but trust us, you will get used to it, and your awareness of the line will diminish greatly as you do.

Progressive addition lenses are seamless multifocals. These lenses are much more functional than the blended bifocals. Their design offers a smooth transition from the distance portion of the lens into the reading portion. With progressive addition lenses you can’t see a line from behind the lens. But as your eye moves from the top of the lens through the intermediate channel and into the reading area, the power of the lens gradually increases, or progresses. With this type of technology there’s an appropriate lens power for every viewing distance. Say, for example, you need to view a computer monitor at thirty inches but you’re working from a sheaf of papers just sixteen inches away; all you need to do is look just slightly higher in the lens to bring the computer monitor into view. Because these lenses include an appropriate part for all viewing distances, your vision often seems more natural. For example, say you’re using standard bifocals to peruse the contents of a file cabinet drawer. How well can you see what you’re doing? The files at the back of the drawer are somewhat in focus through the distance half of your lenses, and you can see the files at the front pretty well, using the near portion of the lens. But what about the files in between? To see them requires that you move your head, either closer to the drawer or farther

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away from it. Kind of awkward, isn’t it? The beauty of the progressive addition lens is that you should be able to see the entire drawer, all in focus, all at once.

The drawback to such lenses is that in creating the progressive optics, a small part of the lens becomes unusable and the sides of the lenses become distorted. Still, the technology for crafting these lenses has improved greatly since the late 1970s, when they were first made, and the peripheral distortions are much milder in current lens designs. And, as with other kinds of lenses, you do grow accustomed to the slight inconveniences. At first, when you glance to the side with your progressive addition lenses, your vision will appear wavy, and you’ll probably find yourself looking at things with your whole face, pointing your nose toward whatever you’re observing. However, after you fully adapt to your new lenses, you’ll hardly notice these distorted areas.

Glass or Plastic?

Here’s another big decision: selecting the lens material. Sure, lenses are made from either glass or plastic, but that’s just the tip of the iceberg. Many more choices lie within these two major categories.

Glass lenses tend to be more scratch-resistant than plastic lenses, but you pay the price: they’re also twice as heavy. Plastic lenses are usually the lens of choice because of the weight difference; also, with special coatings, they can become more scratch-resistant. Plastic lenses have other advantages as well. They’re more impact-resistant

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than glass. As a result, they’re less likely to shatter or break. And because they’re less brittle than glass, plastic lenses are easier to work with, which means that they can be machined to fit into more types of frames than glass lenses.

Also, manufacturers can tint plastic lenses simply by dropping them into a vat of heated dye, where they soak up the tint like a sponge. The amount of tint can be varied by the amount of time the lens is left in the dye. And later, if you decide that your lenses are too dark, the tint can be bleached out. On the other hand, glass lenses that are tinted must usually have a coating applied to the lens surface, like tinted car windows in sunny climates. This coating can scratch off the lens. Until recently, photochromic lenses, which get darker when exposed to sunlight, were available only in glass. Although the newer plastic photochromics have improved greatly, many opticians still feel that the glass ones work better (in terms of how dark the lenses get and how quickly they change).

Other Options

Both glass and plastic lenses can be made in high index. Made of denser material, a high-index lens can bend light more powerfully. The result is a thinner—and, to some, a more aesthetically appealing—lens. Highindex lenses made of glass tend to be almost as heavy as regular glass lenses. But when they’re made of plastic, especially polycarbonate lenses, the lenses are much more lightweight than standard plastic ones.

Other coatings and dyes can be added to lenses to im-

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prove both vision and safety. Antireflective coatings reduce the amount of light reflected off the front and back surface of the lens as well as light reflected within the lens itself. Why is this important? For people with early cataracts, glare can be debilitating and even dangerous. The antireflective coatings can make a tremendous difference in vision, especially for driving at night.

UV protection: Plastic lenses can also be treated with a screening dye to filter out ultraviolet light before it has a chance to enter the eye. Ultraviolet (UV) light, the ultra-short wavelength of light that causes skin damage and sunburn, may also contribute to certain cataracts and retinal problems. Therefore, UV protection is especially important for sunglasses. Sunglasses should have 100 percent filtering for UV-A and UV-B light, the two wavelengths of ultraviolet radiation that affect the eyes. If you’re buying over-the-counter sunglasses, look for ones with labels that say “100 percent UV-A and UV-B filtering,” or “100 percent absorbing below 400 nm” (which means that they filter out all light below the wavelength of 400 nanometers).

Specialty Eyeglasses

If you’re shopping for safety eyeglasses, look for frames with side shields and for more impact-resistant lens materials such as polycarbonate or glass that is at least one and a half times thicker than standard glass lenses. Polycarbonate lenses are a good choice for people with one eye who wear glasses, since they provide protection for the remaining eye.

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Occupational lenses are custom-designed to match specific needs with particular activities. Say you need to look above your head at something close up—as a mechanic does, for instance—and you wear bifocals. The object will be blurry through the distance portion of your lens. An occupational bifocal can be made with a second bifocal segment placed in the top of the lens— just like the one at the bottom of the lens—so that you can focus on what you need to see close up. One of the most common uses for occupational eyeglasses is for the computer. With bifocal computer eyeglasses, you can look at your computer screen through an intermediatevision prescription at the top of the lens and still see your keyboard through a near-vision prescription in the bottom of the lens.

Next, Finding the Perfect Frames

So many decisions already, and we haven’t even tackled the issue of frames yet! Again, the range of choices can be overwhelming. It’s not unusual for people to spend hours trying on frames, looking in the mirror and soliciting opinions from total strangers. Why is this? Why do we agonize so? One big reason is the long-term commitment involved here. After all, we’re not talking about a pair of shoes or a new hat; most of us wear the same pair of eyeglasses all day, every day, for years. Therefore, we find ourselves in the quandary of attempting to find the perfect frames, ones to match our entire wardrobe (or, a tougher assignment, ones to match our every mood).

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First of all, relax. You don’t have to go through every single pair of frames in the store. The optician can usually help narrow down your choices, and lighten your burden considerably, by guiding you to a selection that will look best with your particular prescription and facial structure. Note: Don’t let anybody talk you into buying huge frames—that is, unless you want them—simply because “your prescription is so strong.” In fact, if you have a very strong prescription you’ll probably want to choose a frame as small as possible to help reduce the thickness and weight of your lenses. Other considerations are the shape of your face and nose. If you have a round face, for instance, you probably won’t want to choose a perfectly round frame that exaggerates this. If the bridge of your nose is uneven, metal frames may fit better than plastic ones; metal frames typically have nose pads that can be individually adjusted for each side of your nose. Lifestyle is an issue as well. For instance, if you perspire a lot, because you exercise strenuously or live in a hot, swampy climate, you may prefer plastic frames; salt, produced by sweat, can be corrosive to metal frames, damaging the frame and causing skin irritation wherever the frame touches the face.

Our advice? Because this is a decision you’ll most likely have to live with for some time, take a trusted friend or family member with you. Note: Some understanding opticians will allow you to purchase a frame to take home, try on for everyone, and return for credit toward another frame if your family and friends don’t like your new look.