Ординатура / Офтальмология / Английские материалы / The Eye Book A Complete Guide to Eye Disorders and Health_Cassel, Billig, Randall_2001
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tint, and edge configuration. And we can’t stress this point enough: because contacts are worn on the eye, they automatically become a health consideration for your eye. If you choose to shop elsewhere for your lenses, careful fitting and follow-up care must be done before your doctor can give you a written prescription and the goahead. Think about it: You can’t reasonably expect your doctor to see you for an initial contact lens fitting and then write a prescription for you to get your first lenses elsewhere, because if that prescription is not correct, there can be serious complications for your eyes. Sometimes it takes a follow-up visit for the doctor to ascertain that a lens needs to be modified to improve your vision or comfort.
Wearing Your New Contact Lenses
Once you have your contacts, either the doctor or a trained contact lens technician will show you what to do: how to put the lenses in and take them out, plus how to clean and care for them. You’ll also be given a wearing schedule—a plan that tells you how many hours at a time to leave your lenses in your eyes—so that you can get used to them gradually. (It’s like starting an exercise program: you can’t just start out at full throttle, you have to build up to it.)
Contacts do take a little getting used to. The cornea has to adjust to receiving slightly less oxygen from outside air (this doesn’t harm your cornea in any way). Your tear-making system has to gear up production so that it
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can maintain a contact lens as well as your eye. Therefore, follow the schedule faithfully. If you try to wear your lenses all day right away, you’ll likely find yourself right back in the doctor’s office the next day with painful red eyes. (It won’t make you feel any better to recognize that you should have known better.)
Before you leave the office with new lenses, your doctor will probably want to check the fit and also make sure that your vision is what it should be. (Note: Your vision may be slightly blurry at first; this is perfectly normal, because your eyes are adapting.) If it’s determined that the fit looks healthy and that your vision is adequate, then you’ll be set up for your first follow-up visit. (Depending on your specific needs, that visit may be scheduled from twenty-four hours to two weeks after this one.)
The follow-up visit is very important, so don’t cancel yours! It means far more than just seeing that you’re comfortable and making sure that your vision is okay. The big reason to go is this: contact lens complications, if caught early, are always reversible.
The doctor needs to check the integrity and health of your eye at every follow-up visit. A typical follow-up schedule for a first-time daily-lens wearer might be visits at one week, one month, and six months, and then a full examination at a year. Someone with extended-wear contacts might return within twenty-four to forty-eight hours, at one week, one month, three months, and six months, and then at a year for a full examination. If you seem particularly likely to develop complications with
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extended-wear lenses, your doctor may want to see you every three months—or more often, if necessary—even if you’ve been wearing lenses for years.
Taking Care of Your Contact Lenses
Solutions
To help launch you into the new world of contact lenses, your doctor or lens technician will probably give you a “starter kit”: various bottles of solutions, or “lens care systems.” These have been fully tested, under the watchful control of the FDA, to make sure that the solutions work well with each other and that they’ll both clean and disinfect your lenses.
Whether you wear soft, hard, or RGP lenses, the basic steps are the same, and they’re fairly simple: when you take the lens out of your eye overnight, it needs to be cleaned, rinsed, and stored in a disinfecting solution. Some of the soft-lens solution terms that you need to be familiar with are saline, daily or surfactant cleaners, weekly or enzyme cleaners, and disinfection.
Saline is a rinsing solution, made up of water and 0.9 percent salt—much like your tears. Note: If you use tap water instead of saline, you will contaminate your lenses with bacteria and other microorganisms that can cause severe corneal infection. Saline can be preserved with a chemical to keep it sterile for a longer shelf life. (Some people are sensitive to these preservatives, however, and need to use an unpreserved solution.) Any time you need
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to rinse a lens, or temporarily store a lens in a case, use saline. Homemade saline, made with salt tablets and distilled water, carries a high risk of infection because of the potential for growth of microorganisms in the water. One particularly dangerous microorganism, acanthamoeba, can cause a potentially incurable infection.
Daily cleaners are to be used whenever a lens is left out overnight. (If you take your contacts out every day, you’ll need to clean them every day.) If you have extendedor flexible-wear contacts, you’ll need to use the daily cleaner whenever you choose not to sleep with your lenses in. This cleaner is a surfactant, or soap, that cleans debris and other filmy coatings off the lenses. Daily cleaners help disinfect by killing any bacteria that stick to the surface of your lens, and this in turn helps your overnight storage solution do a better job of killing the remaining bacteria.
Protein coatings that also accumulate on the lenses cling so tenaciously that a daily cleaner just isn’t powerful enough to get rid of them. Weekly cleaners contain enzymes that “eat away” the proteins without damaging the lenses. (For some people, protein builds up so heavily that it’s necessary to clean the lenses with enzymes several times a week.) This usually involves either soaking the lenses separately, in a solution of saline mixed with an enzyme tablet—which fizzes like a tiny Alka-Seltzer— or adding the enzyme tablet to the disinfection cycle.
Disinfection is the process of killing bacteria on the lens surface and within the lens itself. Wearing a sterile lens reduces your risk of developing an eye infection.
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(Because soft lenses are porous enough to allow water to pass through, bacteria can infiltrate them as well.) Disinfection systems are described below.
Caring for Soft Lenses
You should always wash your hands before caring for your contact lenses. Before you remove each lens, put “contact lens rewetting drops” in your eye to soften and loosen the lens. (This makes removing your lens a lot easier; it also decreases the risk of either tearing your lens or scratching your eye in the process.)
Cleaning and Rinsing
Once you’ve removed the lens, place it in the palm of your hand concave side up—so that the lens forms a small bowl—and rinse with saline to keep it from drying out. Add several drops of cleaner and gently scrub the lens in your palm by rubbing your finger back and forth over it. (This way you’ll be washing both sides of the lens at once; the outside of the lens will be cleaned as it rubs against your palm.) Alternatively, you can clean one side and then flip the lens over to clean the other. After scrubbing the lens, move it to your other palm and rinse it thoroughly with saline. If you don’t rinse thoroughly, the soap and coatings will reattach themselves to the lens surface, just as food does on dishes that are scrubbed but not rinsed. If you have a “multipurpose” lens solution, in which the cleaner is mixed with the rinsing solution (see below), you can scrub and rinse in the same palm. You should always clean your lenses before disinfecting them.
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Disinfecting
There are three basic systems for disinfecting your soft lenses: heat, chemical, and peroxide oxidative.
Heat systems are designed to warm your contact lenses to a temperature hot enough to kill bacteria that would otherwise grow on the lenses overnight. After each lens is cleaned and rinsed, it is placed in the heat unit. The unit heats the lenses for approximately thirty minutes and then has a fifteento thirty-minute cool-down cycle.
Heat systems are quicker than most other methods of disinfection. Another advantage is that the lenses can be heated in saline that is “unpreserved” (a good option for people sensitive to solutions that contain preservatives and chemicals). There are several disadvantages, though. Heating a lens often makes lens coatings, particularly protein coatings, worse. If your lens is not thoroughly cleaned before you put it in the unit, protein coatings will be denatured (broken down) by the heat and will bind more tenaciously than ever to the lens surface (the “baked-on, caked-on” effect). Excessive protein buildup can not only make your contacts seem constantly cloudy; it may even lead to a particular allergic reaction to your lenses. (For more on this, see below.)
Another disadvantage is that heat units are compatible with only certain kinds of soft lenses. If your lenses are composed of more than 50 percent water, they can’t be heated safely without distorting the lens. (Therefore, check with your doctor before using this kind of system!)
Heat units also have a practical disadvantage: they
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don’t travel well. Wherever you go, you’ll need to be sure there’s someplace to plug in your heat unit. (This isn’t always as easy as it sounds, especially for people who like to camp.)
Chemical disinfectants: If you don’t heat your lenses, you’ll need to soak them in a chemical bath to kill bacteria. With most of these systems, you place your (freshly cleaned) lenses in a case with a solution. This salinebased solution is mixed with a chemical preservative strong enough to kill specified bacteria in about four to six hours. (The solution has to work within a reasonably short time so that you’ll be able to use the lens the next day.)
The advantage to these chemical baths is that unlike the heat system, they don’t make lens coatings worse. However, the big disadvantage is that many people are sensitive to the bacteria-killing chemicals in the disinfectant; some soft-lens disinfection preservatives produce reactions in as many as 40 percent of the people who use them. For many people these reactions are fairly minor: just a little stinging and redness. But for some the effects can be much more serious: a full-blown allergic reaction, with significant swelling of the eyelids and conjunctiva, as well as toxic reactions that leave deposits in the cornea. (For more on this, see below.)
Peroxide oxidative disinfectants: The most significant advance in chemical disinfectants came in the early 1980s, with the development of peroxide oxidative solutions. These are based on a 3 percent hydrogen peroxide solution—the same strength as the hydrogen peroxide
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you can buy in the drugstore. Hydrogen peroxide is a great disinfectant, but it’s acidic; if you accidentally got some in your eyes, it would burn, leave your eyes red, and possibly cloud your vision.
To avoid this, peroxide oxidative disinfection systems have a built-in “neutralization mechanism” that oxidizes hydrogen peroxide, breaking it down to its basic components, oxygen and water. The specifics vary, depending on your particular system. One company, for example, uses a catalytic disk, made of plastic that’s been coated with a very thin coating of platinum. This disk is left overnight in the lens case, where it takes about six hours to break down the hydrogen peroxide. Another company’s solution uses a tablet that contains catalase, an enzyme that also occurs naturally in the body, and that breaks down hydrogen peroxide completely. This system has appeared in several different formats over the years, but the most recent version has a time-release tablet that neutralizes in a two-hour cycle.
These peroxide oxidative solutions have the advantage of combining the best of the two previous concepts. That is, the lenses are not heated, there are no residual chemicals to cause irritation, and these solutions disinfect better than multipurpose solutions (see below). Even when—as inevitably happens in bathrooms full of sim- ilar-looking bottles of solutions—people put the disinfectant directly into their eye, there’s no harm done beyond some temporary stinging and redness. (If this should happen to you, immediately wash your eye with copious amounts of saline and call your doctor.)
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Multipurpose Solutions
In the 1990s, multipurpose solutions, featuring chemical disinfectants plus a cleaner, came on the market. The chemicals are designed to be mild enough to be tolerated directly in the eye, so the solution can be used for rinsing the lenses as well as disinfecting them. These solutions are convenient, which is their best selling point. But any cleaner—no matter how mild—has the potential to cause eye irritation, and the more chemicals, the greater this potential. These systems, however, seem to cause problems only for about 5 to 15 percent of the people who use them, depending on the brand of solution.
Multipurpose solutions don’t always make the most effective cleaners or disinfectants. Because the ingredients have to be mild enough to be tolerated by the eye, they don’t always do as thorough a job maintaining a contact lens over the long run as other solutions. However, they are an excellent means of lens care when lenses are made for frequent replacement, especially if you replace your lenses at least once a month. Often a frequentreplacement lens can be fully maintained with multipurpose solutions—which means you won’t have to bother with weekly enzyme cleaners. (Because everyone’s tear composition, environment, and wearing habits are unique, there are some people who can successfully maintain a pair of contacts for its typical twelveto eighteen-month life with only a multipurpose solution.)
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What’s Next?
In the future you might see some new advances in soft-lens disinfection. Several research groups have tried using a microwave oven as the disinfection unit, and others have experimented with a disinfection unit based on ultraviolet light. Either of these methods would completely sterilize the lenses in approximately five minutes. The significance of this? When a lens is merely disinfected, only certain microorganisms are killed (the ones that cause problems, we hope). A sterilized lens, on the other hand, is utterly free of all living organisms. These ideas are still experimental and must be further tested to ensure that the lenses aren’t somehow damaged during the disinfection process. However, if the soft-lens industry continues in its trend of disposability, all disinfection systems may become obsolete in the future.
Caring for Hard and RGP Lenses
The concepts in cleaning hard and RGP lenses are the same as for soft lenses, but the solutions used are very different.
The first step after removing your lenses is to clean each one thoroughly, on both sides, with an RGP cleaner in the palm of your hand. Use a finger that’s softer than the index finger on the tip, such as your ring finger or pinkie, to reduce the risk of scratching your lens. If you try to clean an RGP lens between your thumb and forefinger, the lens will be more likely to warp because of the extreme pressure from your finger.