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Although nearly 36 million Americans wear contact lenses, not everyone wears them to correct vision problems. Celebrities use contact lenses to change the color of their eyes, athletes put them on to give them extra-sharp vision on the field, and others use them to make Halloween costumes more realistic.
In this article, we'll learn how contact lenses correct sight, look at the variety of lens options that are available and find out how to wear them safely.
What are Contact Lenses?
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Inserting a contact lens
Contact lenses are closer to natural sight than eyeglasses. They move with your eye and correct the refractive error closer to the eye to allow for a more natural field of vision. They don't get in the way of your line of sight, like glasses can. Contact lenses can be worn all day, or even several weeks at a time, so you don't have to worry about putting them on and taking them off.
Contact lenses stay in place by sticking to the layer of tear fluid that floats on the surface of the eye. Eyelid pressure also holds them in place. As the eye blinks, it provides lubrication to the cornea and helps flush away any impurities that may have become stuck to the lens.
Next, we'll look at some vision problems and find out how contact lenses can correct them.
Vision Problems and Contact SolutionsBefore we begin talking specifically about contacts, let's review how vision works and how lenses correct refractive vision problems. If you've already read How Vision Works and How Refractive Vision Works you may want to skip to the next section.
For people with normal vision, light rays enter the cornea in the front of the eye and are focused into a single point on the retina in the back of the eye. Once it hits the retina, the light is converted into signals, which go to the brain to be processed into images.
Sometimes the cornea doesn't focus light precisely on the retina because of a refractive error. The contact lens refracts, or bends light, so that it focuses correctly on the retina. Its shape is based on the type of vision problem that needs to be corrected. How much the lens bends light, or its strength, is expressed in diopters. The higher the diopter, the stronger the lens.
If the eyeball is too long, causing it to focus light rays in front of the retina, the result is myopia, or nearsightedness. People with myopia can see clearly close-up, but their distance vision is blurry. To correct myopia, the contact lens is thinner at the center than at the edges. These lenses are called minus, or concave. They spread the light away from the center of the lens and move the focal point of the light forward, so that it reaches the retina.
Hyperopia, or farsightedness, happens when the eyeball is too short, causing it to focus light rays behind the retina. People with hyperopia can see clearly far away, but their close-up vision is blurry. To correct hyperopia, the lens is thicker at the center and thinner at the edges. These lenses are called plus, or convex. The lens bends the light toward the center and moves the focal point back so that light is focused on, rather than behind, the retina.
An irregularly-shaped cornea causes light to focus at several points, distorting vision. This is called astigmatism. To correct astigmatism, the lens is designed specifically to the individual's correction needs. Whereas lenses used to correct myopia and hyperopia are spherical (the power correction is the same throughout the lens) astigmatism requires a special lens, called a toric lens.
Toric contact lenses are made from the same materials as spherical lenses, but they have different angled curvatures to correct vision specifically for each individual. Toric lenses may be thicker in certain parts of the lens and thinner in other parts. They have two powers: one to correct for astigmatism, and the other to correct for myopia or hyperopia, if needed. They are also weighted more along the bottom or have thin edges along the top and bottom to keep them fixed in one position on the eye.
With presbyopia, the eye loses its ability to accommodate from near to far focus. This often occurs as people get older. Because presbyopia requires both near and far correction, people with this error often require special bifocal or multifocal lenses:
Some people with presbyopia may need a technique called monovision. It uses the dominant eye for distance vision, and the other eye for near vision. Each eye is fitted with a different lens appropriate for the vision correction needed.
In the next section, we'll look at the different types of contact lenses available.
Types of Contact LensesOriginally, all contact lenses were made of a hard plastic called polymethyl methacrylate (PMMA). This is the same plastic used to make Plexiglas. But hard lenses don't absorb water, which is needed to help oxygen pass through the lens and into the cornea. Because the eye needs oxygen to stay healthy, hard lenses can cause the wearer a lot of irritation and discomfort. The upside to these lenses is that they are relatively easy to clean because bacteria don't stick very well to them.
Soft contact lenses are more pliable and easier to wear than hard lenses because they're made of a soft, gel-like plastic. Soft lenses are hydrophilic, or "water loving," and absorb water. This allows oxygen to flow to the eye and makes the lens flexible and more comfortable to wear. Many companies bill their soft contact lenses as "breathable" because they transmit a high amount of oxygen to the eye. Letting more oxygen reach the eye means that you can wear soft contact lenses for longer periods with less chance of irritation.
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Colored contact lenses
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"Cat eye" cosmetic
- Daily-wear lenses - You remove these each night before going to bed.
- Extended-wear lenses - You can wear these for several days or weeks without removing them.
- Disposable lenses - You can wear these lenses for a day, a week, or even several weeks before throwing them away.
- Color-tinted or cosmetic lenses - These lenses change the color of your eyes or tint them for clearer vision outdoors. Other cosmetic lenses drastically change the eye's appearance. Many people use them for the theater or for Halloween.
- Ultraviolet (UV) protection lenses - These lenses protect against harmful ultraviolet rays from the sun.
- Corneal reshaping lenses - You wear these lenses overnight and they gradually reshape the cornea to correct your vision. When you take them out, you can temporarily see clearly without contact lenses.
Rigid, gas-permeable lenses, which were developed in the late 1970s, are made from a combination of PMMA, silicone, and fluoropolymers (a type of porous plastic). These lenses combine some of the features of hard and soft contact lenses. They're more durable than soft lenses, but they still allow oxygen to pass into the eye, making them more comfortable to wear than hard lenses. Because they don't contain water, they are less likely to develop bacteria and cause infection than soft lenses. The rigidity of the lens provides clear, crisp vision.
New sport-tinted contact lenses filter out certain wavelengths of light to sharpen visual details for athletes. They also reduce sun glare and protect athlete's eyes from harmful UV rays. The lenses come in amber and gray-green. Amber works best for fast-moving sports such as baseball and soccer. It blocks out annoying blue light and accentuates the reds. Gray-green is best for slow-moving sports, such as golf, that are played in the bright sunlight. Currently only professional athletes can get these lenses, but they should be available to the public by the summer of 2006 and should cost about the same as regular contact lenses.
Special Contacts for Special Conditions
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ProClear Compatibles are designed specifically for people with dry eye syndrome.
- Have a history of corneal infections
- Work in an industry where they are exposed to chemical fumes, dust, or dirt
- Have allergies to lens-care products
- Are diabetic
- Are under the age of nine
People with keratoconus have a thinning of the cornea that causes a cone-shaped bulge. A hard, gas-permeable contact lens is most effective for people with this condition, because it stays fixed on the cornea. People with extremely distorted corneas may need a piggybacking technique, in which they wear two lenses on each eye. A soft lens sits right on top of the cornea, and a gas-permeable lens is placed on top of it.
Giant papillary conjunctivitis is an inflammatory condition in which the eyes secrete proteins. Soft contact lenses don't tend to work well for people with GPC, because proteins deposit on the lens of their eyes and cloud them over. Daily disposable daily contacts may work better, because the proteins don't have enough time to accumulate. Hard, gas-permeable lenses also can work because the proteins don't tend to stick to them.
We'll discuss how to get and take care of contact lenses in the next section.
Today you can buy contacts from mail-order catalogs, over the phone and on the Internet. You still need a current prescription, though. The Food and Drug Administration (FDA) advises that you order from a reputable supplier and get a regular check-up from your eye doctor to ensure that your lenses fit properly. Ill-fitting lenses can move around in the eye and scratch the cornea.
Although contact lenses are generally safe, they can cause problems. Usually, the problems are minor, such as eye discomfort, redness, or excess tearing. In rare cases, contact lenses, especially extended-wear lenses, can cause a serious infection called a corneal ulcer. This infection can cause redness, pain, tearing and light sensitivity. If left untreated, it can lead to permanent vision damage.
Infections are most common in extended-wear contacts, because the eyes produce fewer oxygen-carrying tears when they are closed during sleep. But even lenses worn just during the day can cause vision loss if they don't allow enough oxygen flow to the cornea. Failing to keep the lenses clean can lead to an infection, for example with the parasitic Acanthamoeba keratitis. This infection causes symptoms similar to those of corneal ulcers.
You should also be careful if you buy cosmetic lenses at places (such as a flea market or costume store) that don't specialize in contact lenses. Lenses that aren't properly sterilized, or that don't fit your cornea correctly, can cause infections and damage your vision.
Next, we'll learn about the history of the contact lens.
Inventing the Contact Lens
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Leonardo da Vinci
A wearable contact lens wasn't made until the late 19th century, however. English astronomer Sir John Herschel came up with the idea of taking a mold of the eye to make the lens conform to the eye's surface. Then in 1887, a German doctor named Adolf Eugen Fick created the first contact lens that could correct nearsightedness and farsightedness. He first tried his lens out on animals. His lenses were effective, but they covered the entire eyeball and were so heavy that the wearer could only tolerate them for a few hours. In 1889, A German glassblower named F.A. Muller improved upon the glass lens by making it thinner and lighter.
In 1936, a New York optometrist named William Feinbloom introduced the idea of including plastic to make the lens more wearable. However, the lens still sat flat on the cornea, which was uncomfortable and didn't provide the best possible vision correction. In 1948, California optician Kevin Tuohy began making contact lenses entirely out of plastic. They were still bigger than the cornea, but smaller than previous lenses.
Improvements came with a lens shaped more like the cornea in the 1950s. During the 1950s and 60s, lenses became smaller and thinner. For the first time these hard lenses could be worn all day, but they were still uncomfortable to some people. The soft lens became commercially available in the United States in 1971. The 1980s saw the introduction of the color-tinted contact lens, the disposable lens and the extended-wear lens. According to the FDA, 82 percent of contact lens wearers today wear soft contacts [ref].
For lots more information on contact lenses and vision correction, check out the links on the next page.
- How Corrective Lenses Work
- How LASIK Works
- How Light Works
- How Refractive Vision Problems Work
- How Vision Works
- How Artificial Vision Will Work
- What does it mean when someone has 20/20 vision?
More Great Links
- American Academy of Ophthalmology
- American Optometric Association
- Contact Lens Council
- Prevent Blindness America
- "All About Your Eyes." The Contact Lens Council.
- American Optometric Association
- "Buying Contact Lenses on the Internet, by Phone, or by Mail: Questions and Answers." FDA.
- "Contact Lenses." The Cleveland Clinic Health Information Center.
- "Correct Your Vision: Envision the Difference." Bausch & Lomb.
- DeFranco, Liz. "Multifocal Contact Lenses." AllAboutVision.
- Del Pizzo, Nancy. "Contact Lenses for the "Hard-to-Fit" Patient." AllAboutVision. http://www.allaboutvision.com/contacts/hard_to_fit.htm
- Del Pizzo, Nancy and Liz Segre. "Toric Contact Lenses for Astigmatism."
- "Do You Lead an Active Lifestyle?" The Contact Lens Council.
- "E-commerce Increases Choice and Convenience for Contact Lens Wearers." FTC, March 2004.
- Farley, Dixie. "Keeping an Eye on Contact Lenses." FDA.
- "The History of Contact Lenses." Contact Lens Council.
- Rosser, Dr. Paul. "Contact Lenses." Medic8 Family Health Guide.
- "What are Contact Lenses Made of?" Ask Yahoo, July 16, 2002.
- "Refractive Errors." Alcon Labs.
- "Contact Lenses." Prevent Blindness America.
- "The History of Contact Lenses." EyeTopics, November 14, 2004.
- Nike MAXSIGHT Sport-Tinted Contact Lenses FAQs. Bausch & Lomb.
- "New Contact Lenses Clear Baseball's Future." Sporting News, April 21, 2005.