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

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After thoroughly scrubbing your lens, rinse it with tap water. Be sure that the water is not too cold (it might shatter the lens) or too hot (it might warp the lens) and—this is essential—be sure to close the drain! You can use tap water instead of saline to rinse the cleaner off your RGP lenses, because the lens isn’t porous enough to absorb the water. However, you should never use tap water to insert a lens into your eye, because of the risk of infection.

After cleaning and rinsing your lenses, soak them in a case filled with an RGP soaking solution. This solution has preservatives to disinfect the surface of your lenses and make them safe to wear the next day. In fact, you’ll probably use the same bottle of soaking solution to wet your lenses when you insert them the next day. The solution refreshes the lens surface to make it more “wettable” with your tears; with every blink, your tears should coat the lens surface smoothly. When a lens is not “wettable,” your tears will bead up on the lens surface, just like rainwater on a freshly waxed car. Note: Always clean your lenses at night. If you clean a lens in the morning after a night of soaking, you’ll undo all the good that the soaking did. Your lens will lose its surface “wettability” until it’s soaked again for a few more hours. (If you happen to be wearing your lens at the time, this means that the soaking will take place in your eye for the first few hours. As a result, until the lens is properly wettable again, it will feel very dry or seem foggy.)

In general, for any type of contact lens, always use fresh solutions for cleaning and disinfection. Empty out

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your lens case after you insert your lenses. Rinse the case, if necessary, and let it air-dry to kill any bacteria remaining in the case. Bacteria need moisture to survive, so air-drying the case will ensure that you’re placing your lenses in a sterile environment the next time you clean them. A solution that is reused will not be as effective and can possibly lead to an eye infection.

Replacing Your Contact Lenses

Maybe your prescription changed. Or you lost or tore a lens, or your lenses just wore out. Maybe you want to keep a spare pair of lenses handy, in case of an emergency. Maybe you wear tinted lenses, and you want several different colors. Whatever the reason, it’s inevitable: at some point, you will need to replace one or both lenses.

So, where will you go to do this? There used to be just one choice: your eye doctor. But these days there are so many alternatives that you can actually shop around. (Believe us, your doctor is well aware of this and as a result will probably offer competitive prices.) Although most doctors don’t have the buying power of a major lens retailer or discount mail-order business, they can usually come close to the best prices you can find elsewhere.

Why should you buy from your doctor if you can save a few dollars and get the exact same lens from someplace else? With soft contacts the reason is simply that no contact lens manufacturer ever produces lenses with a zero

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defect rate, for either a doctor or a major retailer. Your doctor, however, will be better equipped to troubleshoot a contact lens problem than the retail outlet or mailorder house, as well as make sure that the problem is with the lens and not with your eye. It’s not uncommon, for instance, to receive a lens that’s marked correctly on the bottle but doesn’t perform as it should. It might not be clear for your vision or fit like your old lens. Occasionally lenses are received with a small defect in the material itself that affects how you see or how the lens feels.

Some RGP lenses as well turn out not to have been made to your doctor’s specifications and must be returned to the lab. Also, every lab has its own manufacturing technique; these may vary slightly, and this could alter the fit of even a “brand-name” lens. Say your doctor orders your first lens from one lab, and you replace it with a lens from another lab. Although the lens material and specifications may be exactly the same, the lens still may not fit or perform exactly as your original lens did. Not only can this affect your vision and comfort, it can also harm your eye. If you do shop around for your RGP lenses, make sure that your new lens supplier gets in touch with your doctor’s lab for your exact specifications and tolerances.

The mail-order contact business is booming. You’ve probably seen the commercials and read the ads, in which a spokesmodel suggests that you can now buy lenses using a convenient toll-free number for up to “60 percent less.” Just have your credit card ready! Such ads

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may be misleading. To start with, no lens manufacturer has ever set a “manufacturer’s suggested retail price” for contacts. If you look hard enough, you’ll probably come across a greedy doctor somewhere who overcharges for lenses so exorbitantly that the mail-order company’s price is indeed 60 percent less. But this is not the norm. And it’s not the whole story, either. Most mail-order companies want to sell you a “membership fee,” which adds to the cost of each “discount” lens; they also charge a pretty penny for shipping and handling, and these hidden costs often make the lens price equal to or more than the price your doctor charges. Mail-order companies are in the business to sell lenses and make a profit. Most doctors, in contrast, sell lenses to their patients as a service and charge only a nominal markup to cover any office expenses associated with ordering lenses. Reputable eye doctors make their living caring for eyes, not selling lenses.

So, if you do buy from mail order, be careful. There have been many cases in which mail-order companies haven’t called the doctor to verify the prescription before sending the lenses. Also, mail-order phone representatives often try to sell you other products and services— including lens solutions, or even suggesting their own network of doctors. In some cases phone clerks, dispensing “expert” advice without the benefit of examining the person’s eyes or seeing his or her patient records—or, for that matter, having the medical education to make their opinions valid—have even suggested that a patient wear his or her lenses differently from the

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way the doctor prescribed. And this, frankly, is reprehensible. Your doctor has carefully selected a lens care system that’s appropriate for your lenses and your eyes in particular. Such careless advice could potentially cause damage. Also, your doctor has prescribed a personalized schedule for you so that you can wear your contacts safely. If you’ve been told by your doctor, for example, to dispose of your extended-wear disposable lenses every week, don’t try to wear them for two weeks just because Joe at the mail-order house said you could. (One of the ways mail-order companies promise “big savings” on disposable lenses is by telling you to wear them twice as long—advice that might be easy on your wallet, but tough on your eyes.) Finally, if you like and trust your doctor—and you should, or else you should find another doctor—why change?

Complications: When Something’s Not Right with Your Contacts

Dry Eyes

This is an extremely common problem; in fact, dry eyes are probably the largest impediment to successful contact lens wear. Unfortunately, as the eye gets older, it makes fewer tears. In addition, medications such as hormonal supplements, diuretics, antidepressants, and Accutane can make the eyes dry. Many people who have worn contact lenses for years, with no problems at all, suddenly find themselves unable to tolerate their lenses.

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However, the key may simply be finding the right lens material for your eyes. It may take trying several different lens designs and materials before you and your doctor can find the least-drying contact lens for your eyes.

Tears are more complicated than you might imagine (see chapter 13). They’ve got three major layers, for one thing. The innermost, called the mucin layer, is produced by goblet cells on the conjunctiva. (For more on the eye’s anatomy, see chapter 1.) Mucin is viscous; it enables tears to cover the eye more evenly. The huge middle layer (which takes up about 90 percent of each tear), mostly water, is produced by the lacrimal glands that sit just above and outside your eyes. Outermost is an oily layer, produced by a row of Meibomian glands along the margin of each eyelid; the coat of oil helps keep tears from evaporating too quickly.

A soft contact lens contains water, and so soft contact lenses must absorb tears in order to stay soft. After the lenses have been in your eyes for about fifteen minutes, their water content is actually made up of your tears. If your eyes are dry because of poor tear quality—that is, if you have plenty of tears, but they lack mucins or oils— then a higher-water-containing lens will probably keep more tears on your eyes and, as a result, be less drying. If, however, your eyes are dry because of poor tear quan- tity—if, in other words, your tears are perfectly fine, but there just aren’t enough of them to go around—then a lower-water-containing lens will usually cause less dryness, because it won’t have to absorb as much tear volume to maintain itself. Finally, if you have both poor-

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quality and poor-quantity tears, you’ll most likely have problems wearing soft contacts at all—but RGP materials may work well for you.

Corneal Edema

As we’ve discussed in previous chapters, we see because light passes through the “window” of the cornea and focuses on the retina. The innermost portion of the cornea is constantly in contact with the aqueous humor, the fluid within the eye, but this fluid is never allowed to build up. Tiny efficient “pumps” continuously force it out, to keep the cornea clear (see chapter 11). These pumps run on oxygen; most of it comes from the environment, but extra oxygen also comes from blood vessels around the cornea and under the eyelid.

A contact lens has the potential to decrease the supply of oxygen to the cornea, and this can cause the pump mechanism to slow down. In turn, fluid begins to seep into the cornea—a swelling called edema—causing it to become cloudy. This can happen if a lens is too tight, if it’s too thick, or if it’s worn too long.

Signs of trouble: You’ll probably notice symptoms first when you take out your contacts and put on your glasses: your vision will look hazy. If this haziness disappears within the first ten to fifteen minutes, the edema is probably not very significant. However, the haziness can persist for days or even months, depending upon how much edema was present. If the edema is left untreated, small water bubbles will eventually form in the cornea. Your cornea is like skin, in that the surface layer constantly re-

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plenishes itself; cells formed below the surface rise and eventually slough off. When edema is present, these bubbles float along with the rest of the cells right to the top. When they reach the surface of the cornea, they burst, leaving tiny abrasions. If you accumulate enough of these abrasions, in addition to the hazy vision you will have red and painful eyes.

Treatment: Your doctor can prescribe drops or ointments to reduce the edema and heal the abrasions. Corneal edema almost always resolves with treatment and discontinuing wear of the lens that’s causing the trouble.

Corneal Neovascularization

Neovascularization is the growth of new blood vessels. As discussed above, the cornea needs oxygen to maintain its clarity; oxygen also supports a protective barrier that keeps blood vessels out of the cornea. If the cornea is oxygen-starved, blood vessels invite themselves in, taking upon themselves the matter of “turning up” the oxygen flow. Unfortunately, these vessels also scar the cornea.

Treatment: If this condition is caught early, neovascularization can be reversed simply by removing the offending contacts and either switching to a better-fitting, more oxygen-permeable lens or discontinuing lens wear for a time. But when these blood vessels spread unchecked like ivy, right into the center of the cornea, they can cause big trouble: a significant loss in vision that can be treated only by corneal transplant.

Because there really aren’t any early warning signs or

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symptoms of corneal neovascularization—that is, until it’s too late to reverse—routine examinations with your doctor are essential, so that your doctor can make sure your cornea is as healthy as it should be.

Giant Papillary Conjunctivitis

Giant papillary conjunctivitis, or GPC, is an allergy that’s caused by an autoimmune reaction to your own protein coatings, the ones that build up on poorly cleaned contact lenses. Who’s at risk? You are, if you don’t use a weekly protein cleaner with your soft lenses, or if you don’t do a very good job cleaning any type of contact lens.

On any typical day of wearing your contacts, your upper lid travels about three hundred yards—the equivalent of three football fields—over the surface of your lens. The upper lid therefore has the most interaction with protein coatings and is the best indicator of GPC: its inside surface becomes swollen and red and produces large amounts of mucins that coat your contact lens with a film that clouds your vision when the contacts are worn.

Signs of trouble: One common early symptom is an itch that gets worse when you remove the lens (when your upper lid comes in direct contact with your cornea). Also, as more mucins are produced, the lenses begin to appear foggy while you’re wearing them. Some- times—because with each blink your swollen upper lids grab the sticky, coated contact lenses more vigorously than usual—they even slide off the center of your cornea. Lenses also tend to wear out much more quickly

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than normal with GPC. Many lenses designed to last a year will wear out in as little as one to two months. Often someone with this problem will replace many lenses in a short period of time before finally going to the eye doctor and having the problem checked out.

Treatment for GPC has varied over the years, but a common remedy is to stop wearing contacts for at least two weeks, to give the lids a chance to recover. (Often this alone is enough to treat the problem, without the need for any additional medications.) If your GPC is severe, or if you still have symptoms after you stop wearing your lens, your doctor may prescribe antiallergy and/or antiinflammatory eye drops. Over-the-counter artificial tear supplements can also help.

Because GPC is an allergy, if you start using the same contact lenses after this two-week breather your symptoms will probably come back; the proteins will accumulate again and produce a new allergic reaction. Therefore, if you want to keep wearing contacts once the GPC has resolved, you’ll need to switch to another kind of lens. In the past, someone with GPC either moved to a more “deposit-resistant” soft contact lens—and a much more rigorous cleaning regimen, including more frequent enzyme cleaning—or switched to a gas-permeable lens. But in recent years it’s been found that wearing disposable or frequent-replacement contact lenses also reduces the problem dramatically. Because there’s so little buildup of protein on a new contact lens, replacing your lenses every day to every two weeks keeps the lenses free enough of proteins that GPC usually doesn’t return.