Despite the fairy tales, the size of our eyes has very little to do with how well we see. We don't need big eyes. But most of us will—or already do—need big lenses in front of them. In fact, half of all Americans wear glasses, and if you just look at the population aged 45 or older, the number jumps to 95 percent.

While this population includes a lot of different types of people, it's interesting to note that every president of the United States has worn glasses, all the way back to George Washington. Some presidents wore them only in the privacy of their office with the door closed. Others switched to contact lenses.

Even our two youngest presidents wore glasses. John Kennedy, who was elected president at age 43, wore reading glasses, although he rarely let himself be photographed wearing them. Theodore Roosevelt, who was elected vice-president at age 42 and became president shortly before his 43rd birthday (when President William McKinley was assassinated), was usually seen wearing his glasses.

The aging process that makes reading glasses necessary strikes everyone, regardless of race, creed, religion, prestige, or income. And it strikes us all at about the same time, too—in the early forties.

Once you get into your forties, the lenses of your eyes lose their flexibility and need outside help to focus for reading or close work. We'll look at the reasons why in a minute. But first let's take a brief look at the history of eyeglasses, which are also known as glasses, spectacles, specs, magnifiers, and even crutches for your eyes.

Da Vinci Started It All

As with so many other great ideas, Leonardo da Vinci is credited with first coming up with the concept of using magnifying lenses to see better. As technology improved, so did the idea, and the early hand-held magnifying lenses evolved into monocles, which could be held firmly in front of an eye by dint of a dutiful squint.

Since no one can squint all the time without developing a charley horse of the cheek, people kept their monocle on a ribbon pinned to their clothing so that it was always close at hand, even when not close at eye.

Monocles were followed by the lorgnette, two monocle lenses wired together and held to the face with a handle. In the 1600s, craftsmen started joining the two lenses together with a spring-type bridge that held the glasses on the nose.

In 1728 or thereabouts, a London optician named Edward Scarlett invented eyeglasses with temple pieces. But they weren't designed to hang on the ears. Instead they stayed in place by gripping the head in a migrainelike embrace.

It's worth remembering that patent laws weren't very rigid 250 years ago, and it's hard to prove that any one person was the first to do anything. The odds are that reading glasses—like the wheel, shoes, and rock and roll—were an idea whose time had come. They were probably developed by a number of different clever people working independently.

Take, for example, the case of bifocals. Tradition states that Benjamin Franklin should get the credit for that one, because he crafted glasses that combined an upper lens for distance vision and a lower one for near vision. Franklin first wrote of his invention in 1784. But London opticians had been experimenting with the idea for more than 20 years by that time, and other people had been writing about the concept since at least 1716.

But regardless of who first actually made that optical breakthrough or any of the others, those early glasses were designed to do the same thing Leonardo da Vinci's magnifying lenses were designed to do centuries earlier—correct a few of nature's mistakes.

The Most Common Vision Problems

Still thinking about the human eye as a camera, picture a series of lenses at the front of the eyeball that bend light and focus it into an image recorded on the retina in the back of the eye.

If the eye is perfectly shaped, and the distance between the cornea (lens) and the retina (film) is exactly right, the image projected on the retina is in perfect focus—crisp, clear, and sharp. That's exactly the sort of image that about half the population below the age of 40 sees naturally. But the other half of the population doesn't see it correctly, and here's where glasses come in.

Glasses—and contact lenses, are primarily used to correct four different but depressingly common vision problems: nearsightedness, farsightedness, astigmatism, and presbyopia. To complicate matters, some people suffer from two or more of the four. In each of the four, however, the lenses in the glasses have to compensate for the eyes' natural limitations.

Nearsightedness

For nearsighted, or myopic, people, the world is a blurry place for one of two reasons. Either their eyes are too long or the focusing power of their eyes is too strong.

Light first carries an image through the cornea and then through the flexible crystalline lens behind it. Eye muscles bend and stretch the crystalline lens to bring objects into focus. The lens also acts as a projector. It projects the image on the retina in much the same way a movie projector puts an image on a screen. With nearsighted people, however, the lens is too powerful, and the image comes into sharp focus before it can reach the retina.

With a slide projector and a portable screen, you can demonstrate the process. Set up the screen and project a slide on it. Make sure you have the image in pinpoint focus. Now move the screen back a few feet.

The image that reaches the screen now is blurry because the screen—just like the retina—is behind the point of perfect focus. To get the image back into focus, you have three choices:

1. Move the screen, which would be the same as moving the retina of the eye.
2. Refocus the projector's lens. Some people manage to refocus by squinting, which puts a little more concentrated focusing power into their eye, but squinting becomes rather tiresome after a while.
3. Add an additional lens in the form of glasses. Properly prescribed and made, lenses will change the distance the image travels to make sure it ends up on the retina in perfect focus.

A myopic person doesn't always need glasses to see everything, just things that are far away. Near objects can often be focused on quite easily.

Myopia, or nearsightedness, is the single most common focusing or refractive problem. Most of the people you see wearing glasses are myopic. While about half of all the people with myopia have focusing systems that are just too powerful, the other half have eyeballs that are just a tad too long. The cornea, which is the most powerful lens of the eye, works just fine, but the retina isn't where it's supposed to be.

Let's assume that the lens on our slide projector was built to focus on a screen exactly 20 feet away. But when the projector is set up and locked into place in the projection booth, the screen is 22 feet away—and cannot be moved. The lens is doing its job, but the screen is in the wrong place. So whether you were born with a focusing system just a tad too strong or an eyeball just a smidgen too long, the effect is the same. You need glasses.

Farsightedness

Now let's look at the world through the eye of a farsighted person, a person with hyperopia. Instead of focusing the image right on the retina, the farsighted person's lens system focuses the image behind the retina.

The image reaches the retina before it comes into focus. Take the projector and screen and set it up again so that the image is in perfect, pinpoint focus. Now instead of moving the screen backward, move it forward 2 feet.

The picture is out of focus.

While a nearsighted person needs glasses that will move the focal point back, a farsighted person needs glasses to move the focal point forward. If you have farsightedness, or hyperopia, you can see distant things reasonably well. Your problems begin when you have to look at something close up.

Only about 10 percent of the people who wear glasses have to do so because they are farsighted. Like their nearsighted cousins, hyperopic people can be farsighted for two different reasons. Either the focusing power of the eyes is too weak or their eyeballs are a bit too short.

Again, glasses can correct either problem.

Astigmatism

While people with myopia and hyperopia have problems with the focal length of their lenses, people with astigmatism have problems with the shape of their cornea and lens. There are three things to remember about this.

1. A "perfect" eye is perfectly round.
2. An astigmatic eye isn't perfectly round.
3. No one has a perfectly round eye.

Everyone has a bit of astigmatism in either the lens or the cornea—or both. It's a matter of degree.

The astigmatic eye has at least two different curves, and instead of looking like a baseball, it can—in some cases—be shaped more like a football, or a basketball with a beer belly.

In most people the degree of astigmatism is usually so slight that there is no problem. But if the astigmatism is bad enough to cause blurry vision, glasses are needed.

Why does an astigmatism cause blurry vision?

A slide projector's lens is rounded so that the different light images that hit it anywhere on its surface will all travel the same distance to reach the focal point—the screen. What's more, the images will all make the trip in the same time.

Now imagine focusing through a glass football. Because it's not perfectly round, the images hitting it at different spots on the surface will have different distances to travel to reach the focal point. As a result, some of what you see will appear to be in perfect focus, and some of it will appear distorted.

For a more extreme example, let's look at a mirror in a carnival funhouse. Since the surface is distorted—bent out of shape—light hitting it will reflect back distorted images. Depending on the curves in the mirror, your "mirror image" could show you with short stubby legs, a belly the size of a truck, and a neck like a giraffe's.

Of course, if you actually do look like that, your image in a distorted—astigmatic—mirror could make you look sexier than your favorite TV star. As proved by countless movies and magic acts, you can do amazing things with mirrors.

Luckily, most corneal astigmatism is not as exaggerated as that found in a funhouse mirror, but even a slight degree of astigmatism is enough to cause problems—a wide variety of problems.

Depending on the shape your eyes are in, part of what you see could be perfectly focused while other parts could be perfectly fuzzy. That's because part of the image could come through the cornea and crystalline lens and wind up in focus right on your retina, and another part could wind up just in front of the retina or just behind it.

Astigmatic eyes could also focus both images in front of or behind the retina, or partially in front of and partially behind, or ...

You get the idea. The possibilities are enough to make your eyes ache just thinking about them. The important thing to remember is that there is a solution. The distorted astigmatic image that hits your retina can be corrected with glasses ground in curves to compensate for the curves nature threw your eyes.

What does an astigmatic person see? Go back to your slide projector, turn it on and focus it, and then place a clear drinking glass just in front of the lens. Now move it around and see what the images on the screen look like. You can also go to a carnival funhouse and look at yourself in the mirrors.

Or go to the library, check out an art book, and study some of the paintings of El Greco. Many people believe that Spain's most famous Greek painter—El Greco means "the Greek"—had an uncorrected astigmatism, which got worse as he got older. If so, this would explain why the figures in his paintings are so long and thin.

Presbyopia

While myopia, hyperopia, and astigmatism happen to only some of the people, presbyopia happens to all of the people—if they live long enough. It's a natural part of growing older.

The eye has a remarkable mechanism for changing its power—or focal length—to look at something close, such as the text of this article. The eye can do this because the crystalline lens behind the cornea stretches.

When you are reading or looking at your watch, a reflex contracts one of the eye muscles, causing the crystalline lens to automatically fatten a bit. This brings a close object into sharp focus. This is called the accommodation reflex.

As you get older, though, the crystalline lens loses its flexibility. It's a gradual process. While you once might have been able to read a phone number out of a phone book as soon as you opened it, you may notice that you have to squint a bit to bring the fine print into focus.

At a certain point—usually in your early forties—you'll have to trade in your squint for a pair of reading glasses, or give up on phone books completely.

Presbyopia has struck again.

It will continue to strike, reducing your eye's elasticity year after year so that you will need even stronger reading glasses until, at about age 65, the process stops. Your eyes won't change much after that.

While presbyopia does strike everyone, it doesn't leave everyone needing reading glasses. If you have just the right amount of nearsightedness, you may be able to simply take off your regular glasses to read. It's like having built-in reading glasses. Of course, distance vision will still be blurry for nearsighted folks, but you could be the envy of all your friends when you take off your glasses to read the restaurant menu or the fine print in the phone book.

Special Glasses for Special Needs

Conventional eyeglasses are made to correct one vision problem and as a result have only one power. No matter which part of the lens you look through, the power, or magnification, is pretty much the same. But presbyopic people need a different power for near vision than they need for distance vision.

Bifocals solve this problem by providing two separate lenses for each eye. The upper one is for distance vision and the lower one is for near vision.

Trifocal glasses incorporate three lenses: an upper lens for distance, a lower lens for reading or close work, and an intermediate lens for the middle distances. Trifocals are especially useful for typists and piano players. While bifocals and trifocals are convenient, they can take a little getting used to, since your vision "jumps" as your eyes cross the line between the lenses.

That line can also be a major ego problem. Many people look at bifocals and trifocals as something that only old people wear, and are willing to put up with all sorts of inconvenience, annoyance, embarrassment, and outright danger rather than have people think they are getting old.

One way around the line problem is with "seamless" bifocals. They blend the distance and close-up portions of the lens without the telltale bifocal line. These can work very well and should be considered by those who are annoyed—or embarrassed—by ordinary bifocals.

Because they are more difficult to grind accurately, they do cost more than conventional bifocals, but many people consider them worth the extra expense. Of course, if you've already gotten used to regular bifocals or trifocals, it may be difficult to adjust to the different focusing system of the seamless bifocal.

Another way to solve this problem is with two different pairs of glasses. Not only is it inconvenient, it is also more expensive, because you need to have two complete pairs of glasses.

Safety Glasses

All prescription glasses are required by law to be impact resistant and meet specific safety requirements. Under the regulations, if a 5/8-inch-diameter steel ball bearing were to be dropped on one of the lenses from a height of 50 inches, no fragments should fly into the eye.

The standards for industrial safety glasses are even tougher. Such lenses must be at least 3 millimeters thick and capable of withstanding the impact of a 1-inch ball bearing dropped from 50 inches. In addition, the frames must be both sturdy and flame resistant.

Either glass or plastic lenses may be used for either regular or safety glasses. Plastic lenses do scratch more easily than glass lenses, but because they weigh only half as much as glass, many people find them more comfortable.

Today, however, the development of lighter-weight glass lenses and more scratch-resistant plastic ones is minimizing the differences between the two types of lens.

Sunglasses

Sunglasses are a lot older than reading glasses. They may even be older than glass.

Unknown centuries ago, Eskimos started making an early form of sunshade to prevent snow blindness. They would carve an eye "mask" out of wood and put in narrow slits to look through. The slits gave them enough of a view to work with, and because they were so narrow, they blocked out the glare that could have caused snow blindness.

Five Myths about Glasses

There are myths about four-leaf clovers, dogs named Rover, golden jars, and shooting stars, so, of course, there are myths about glasses, too. And many of them make as much sense as the one about four-leaf clovers bringing luck. Here are five of them:

1. Wearing glasses will strengthen your eyes. Glasses don't change your eyes at all. What they do affect is your vision, by giving your brain a clearer image of what your eyes see.
2. Wearing glasses will weaken your eyes. See myth number 1.
3. Wearing glasses will make you "addicted" to wearing glasses. The only habit that wearing glasses develops is the habit of actually seeing what's going on around you—and seeing it clearly and distinctly.
4. If you have a lot of headaches, you need glasses. If you have a lot of headaches, it means that you have a lot of headaches. Because the vast majority of headaches are tension or stress-related, the odds are you are under a lot of stress. A small number of headaches can be classified as migraine headaches. High blood pressure, sinus infections, allergies, and tumors can also cause headaches. Rarely will people develop headaches because they need glasses. Those who do are usually farsighted and develop headaches when they read for a long time without wearing glasses. When they stop reading or start using glasses, the headaches will usually disappear.
5. Glasses make you smarter. Obviously a conspiracy started by the people who manufacture glasses, this one is based on appearances. For reasons better dealt with by practitioners of cultural anthropology than of ophthalmology, we tend to think that people who wear glasses look smarter than people who don't. One possible reason is that we associate glasses with people who have weak eyes because they read so much (see myth number 2). But wearing glasses can also make you appear smarter by giving you more time to think. Ask people who wear glasses a hard question and they will very likely take the glasses off and clean them before answering you. They aren't cleaning their glasses because the glasses need cleaning, or to see the problem—or you—more clearly. They're doing it to give themselves a few extra seconds to think of an answer, time they wouldn't have if they didn't find something to do with their hands while they were thinking.

Ancient Tibetans wove fine horsehair into a kind of sun visor. And more than 2,000 years ago, the Chinese wore tinted lenses because of the good luck they supposedly brought—and the bad luck they supposedly prevented. Chinese judges, for example, wore smoked-glass lenses to conceal their thoughts from defendants.

Tinted lenses were worn in the United States in the early 1800s, but they didn't really take off until the first planes did. It was in the 1920s that the U.S. Army Air Corps started looking seriously at sunglasses as a way to help fliers cope with high-altitude glare. The sunglasses market has been flying high ever since.

While many people look at sunglasses as a fashion accessory, they do also provide important visual comfort and protection by cutting down on the amount of visible light, glare, and ultraviolet (UV) radiation that reaches the eyes. The amount of light that does get through is determined by the "transmission factor" of the sunglasses.

Generally speaking, no more than 30 percent of outdoor bright sunlight should be transmitted to the eyes. But if you are at the beach or on the ski slopes, where the sunlight is brighter and there is a high glare factor, a transmission factor of just 10 to 15 percent may be preferable. Manufacturers often attach a tag to their sunglasses listing the transmission factor.

Depending on what you are going to be doing, you might prefer one of the following types of sunglasses:

• Gradient density sunglasses are dark at the top, tapering to clear at the bottom.
• Double-gradient density sunglasses are dark at the top and at the bottom and lighter in the center. They are especially useful for driving, boating, or any other situation where there is a great deal of overhead light and low-level glare.
• Reflective sunglasses have a thin metallic coating that reduces the amount of light that reaches the eyes by reflecting it away.
• Polarizing lenses eliminate vertical glare. They are very effective and often very comfortable.
• UV lenses filter out ultraviolet rays.
• Photochromic lenses adjust to the amount of light hitting them by automatically becoming darker in bright sunlight and turning clear again when the light dims. While many people are happy with automatic sunglasses, others find the process bothersome and too slow.

More and more researchers are tying excessive UV exposure to a number of serious eye problems such as cataracts and macular degeneration. While more work needs to be done to prove this connection, if it is true, glasses that screen out UV light may help slow down these sight-threatening conditions.

In the meantime, what should you do about UV light?

• Be aware that a connection may very well exist. It hasn't been proved yet, but it hasn't been disproved, either. Play it safe, but don't let it drive you crazy with worry.
• Be aware that there are a lot of promoters out there trying to put the fear of God into all of us about the disastrous effects of UV light. And once they have us thoroughly cowed, they pull out their complete line of UV glasses.
• Take some reasonable precautions. Try not to face directly into the sun; wear sunglasses if you spend a lot of time in bright sunlight.

Some research is being done now with sun-screening eye-drops, which would block out potentially harmful UV rays. The drops would last for several hours and would be reapplied as needed. But even if they do work, they won't reduce glare or brightness. Sunglasses will still be around.

Just as sunglasses come in different styles, they also come in different colors. But no matter what the current fashion gurus might dictate, you don't want to look out at the world through rose-colored glasses—or pink, blue, or purple ones.

Neutral gray or "smoke" is the best color. It gives the best color perception and the least distortion. It is also the most difficult tint to produce, and as a result, it is only available in better-quality, more expensive sunglasses.

Green and brown-tinted lenses are also good choices, but forget the silly ones designed by people who think color-coordinating your sunglasses and your shoelaces makes an important fashion statement. Pink, blue, purple, orange, rose, yellow, striped, and polka-dot sunglass lenses look better on a store dummy than they do on you—and are about as useful.

Sunglasses: How to Check for Quality

While sunglass style is important to your ego, quality is important to your vision. But in today's marketplace, where a designer label can often double, triple, or even quadruple the profit margin on an item, a high-class label is no guarantee of high-class quality, or for that matter, of any quality whatsoever. So here is a simple way to judge the quality of a pair of sunglasses:

• Examine them against the light for scratches, streaks, bubbles, blurs, or other flaws.
• Hold them at arm's length and focus on an object with strong vertical and horizontal lines, such as a door or window frame. Move the glasses up, down, and sideways. If the lines waver, then there's a distortion in the lens. (This test works only on nonprescription lenses. With prescription lenses, some distortion may be built into the lens for corrective purposes.)
• Put the glasses down on a white surface to check that the lenses are of equal color and density. Badly matched lenses can affect depth perception and cause eye fatigue.

Eric Rost

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