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

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Infections and Corneal Ulcers

Everybody gets eye infections, whether we wear contacts or not. We all have bacteria around our eyes; most of the time our tears keep them in check, but occasionally those bacteria can take over. A well-fitting, welltended contact lens does not cause eye infections, but it can make any infection worse; the warm, moist space between the lens and your cornea can act as an incubator for bacteria and allow them to flourish.

A corneal ulcer is a severe eye infection. It can be extremely painful—and potentially disastrous when it comes to your sight. An ulcer can permanently scar your cornea and cloud your vision if that scar is inside your pupil.

Who’s at risk? Mostly it’s people who often sleep with their contacts in. A common scenario is this: Say you have a small corneal abrasion, from debris that got trapped under your lens. If you take out your lens for the night, the abrasion will have a chance to heal, and you’ll wake up with no ill effects. But if you sleep with the contact lens in, the bacteria that grow between the lens and your eye can work their way into the abrasion and cause a corneal infection.

If you suspect that you have an infection—your eye is red, with a discharge, or is uncomfortable in any way or is sensitive to light—remove your lens immediately and call your eye doctor. Getting medical attention in time usually means that your eye will heal completely

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and that you can start wearing your contacts again as soon as your eye recovers.

If your infection turns out to be bacterial (caused by bacteria), then your usual methods of cleaning and disinfecting your contacts will probably be enough to save your lenses and enable you to wear them again. But if your infection was caused by a virus, disinfection alone may not be enough to remove the contamination, and the lens may need to be replaced.

Tight-Lens Syndrome

Tight shoes can cause debilitating foot problems. A too-tight shirt collar can hamper your breathing and produce symptoms that mimic a heart attack. Well, your eye doesn’t respond well to tight-fitting garments, either. When a soft contact lens is too tight, it can cause problems ranging from mild discomfort to serious, visionthreatening complications. The trouble is that a tight lens doesn’t make room for your tears to flow underneath the lens and refresh the cornea. Instead, tears tend to pool under the lens and stagnate—like a fetid pond, a perfect breeding ground for nasty bacteria. As the bacteria proliferate, they ooze toxins that create cloudy patches in your cornea, called corneal infiltrates, and cause infections.

A soft lens that’s too tight also smothers the cornea, leaving it constantly oxygen-starved. The chronic lack of oxygen (as discussed above) in turn makes the cornea more susceptible to edema (swelling) and neovascular-

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ization (the growth of new blood vessels within the cornea).

Tight-lens syndrome can happen with any kind of soft contact lens—even disposable lenses that are thrown away every day. If the lenses don’t fit properly, it doesn’t matter how long you leave them in or whether you take them out every night; you’re still harming your eye.

Signs of trouble: Warning symptoms include foggy vision, fluctuating vision (your vision gets better or worse with a blink), dryness, irritation, and redness. Often, redness is noticeable around the entire cornea, but it can appear in isolated patches as well. If the edges of your lens bear down on blood vessels running through your conjunctiva, this can cause tiny hemorrhages to appear around the edges of your contacts. Also, you can almost always see a distinct stamp of the lens left on the eye after you take out the lens, just as you can trace the outline of painful shoes after you take them off your feet. (However, some people can see such an impression even if their lenses fit appropriately.)

An RGP lens that’s too tight can cause similar symptoms, but because it doesn’t cover the entire cornea, as a soft lens does, the symptoms can take longer to express themselves. A tight RGP lens can actually stick to your cornea, making it difficult to remove, and will probably leave a contact-shaped indentation in the cornea afterward. If, after you remove your RGP lens, your vision is foggy and distorted with your glasses—and it doesn’t return to normal within ten to fifteen minutes after you take out your contacts—your lens may be too tight.

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A tight-fitting lens doesn’t necessarily mean that your lens fitter did a poor job of fitting your eye. Contact lenses can tighten on their own after they’re worn for a few hours, especially if your eyes are dry. Thus, it’s important that you have your lenses in for a few hours before you return for any follow-up visit, so that your eye doctor can get an accurate idea of how your contact lenses really fit. (Of course, if your lenses are too uncomfortable to wear for even a few hours, then don’t harm yourself just to demonstrate your level of discomfort!)

Reactions to Contact Lens Solutions

First, read the label. No matter how a solution is packaged, before you buy it, make sure it doesn’t contain any chemical or preservative that you’ve reacted to before. Many manufacturers label their solutions as being “for sensitive eyes,” but even some of these contain preserv- atives—milder, less sensitizing ones, but preservatives all the same—and you may still react to them. Thus, if you need an “unpreserved” solution, make sure the bottle is labeled that way.

Signs of trouble: Sensitivities to preservatives can range from stinging, burning, and redness to full-blown allergic reactions that can cause tremendous itching and swelling and may even harm the cornea. These reactions occasionally require treatment but almost always go away when use of that preservative is discontinued.

Two preservatives known to cause problems for many people are thimerosal and chlorhexidene. Thimerosal

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produces allergic reactions in more than 40 percent of the people who use it; these reactions can develop even after years of use. Chlorhexidene can be toxic to the cornea and can cause significant redness, burning, and irritation. Polyaminopropyl biquanide (also known as Dymed), a newer, milder, version of chlorhexidene introduced in the early 1990s, has decreased this problem tremendously. Still, some people have reactions to this chemical as well (symptoms are similar to those caused by chlorhexidene).

You can avoid some major eye reactions simply by making sure you’re putting the right solution in your eye. Mistakes happen more often than you might think, and it’s no laughing matter. Accidentally putting in contact lens cleaner instead of the rewetting drops you thought you had picked up can cause severe chemical burns, painful red eyes, and cloudy vision that lasts for days or even weeks. Some cleaners contain abrasives that will scratch your cornea; others contain alcohol, which can strip off the surface of your cornea. Occasionally someone mistakes disinfectant for saline, rinses a lens with a disinfectant, and inserts it. This too can cause a significant chemical burn.

Treatment for all of these reactions always starts with removing the offending chemical or preservative. You’ll have to stop wearing your lenses until your eye heals completely, rid your old lenses of every last trace of the chemicals, or replace your lenses altogether. If your symptoms are severe enough, you may also be prescribed a medication. Because your symptoms can be vague,

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when you seek treatment make a list of every solution you’ve been using, or take your solutions along with you, to help your doctor or lens fitter pinpoint the problem.

Of course, one big remedy for solution sensitivities is disposable contact lenses. If you throw them away after every use, you’ll never have to worry about reactions caused by cleaners and disinfectants.

Torn or Damaged Contacts

A torn or damaged lens can irritate your eye, causing symptoms of redness, pain, discharge, watering, and blurred or distorted vision that may not clear up right away when you take out your lens. It may also injure your cornea—in which case you might still feel like the lens is in your eye even when it’s not—or even lead to infection. So if you have persistent redness, pain, or discharge, see your doctor and get your eyes (and contacts) checked.

No matter whether your lens is hard or soft, if it’s torn, warped, broken, or simply worn out, it will have to be replaced. Once they’re damaged, lenses can’t be fixed.

Itching, Burning, and Redness

It’s simple: itching, burning, and redness all indicate that there is something wrong with either your contact lenses or your eyes. If the symptoms go away when you take out your lens, this could indicate a problem with the fit of the lens, the lens itself, or the solutions that you’re using, and your doctor or lens fitter should scrutinize your lens-wearing and lens-cleaning habits to figure out

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what needs to be changed. If your symptoms persist after you remove your lenses, this could suggest an infection, allergic reaction, or abrasion. In any event, you should seek medical attention.

Problems with Extended-Wear Lenses

Extended wear of a contact lens magnifies the risk of any of the complications we’ve discussed above. Think about it: The lens is in your eye twenty-four hours a day. Your eye never gets a break; there’s no downtime. This can cause serious eye infections and complications from lack of oxygen to the cornea.

We’re not all cut out for extended-wear contacts. Some of us require more oxygen in our eyes, just as some of us need more sleep to refresh us or more heat to feel comfortable in the winter. Maybe you can do well with extended wear. Or maybe your eyes have such a high demand for oxygen that you need an extended-wear lens just for daily wear.

In any event, you can dramatically reduce your risk of extended-wear complications by just using a little common sense. The most important thing to do, before you decide to sleep with your contacts in, is to take a good look at your eyes. If they’re red, irritated, or significantly dry before bedtime, then the answer should be pretty obvious: Don’t sleep with your lenses. Take them out. Give your eyes a breather.

If you wake up with any symptoms of redness, persistent blurred vision, discomfort, discharge, or pain, the answer should be equally clear: Take out your lenses im-

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mediately. If the symptoms go away, see your eye doctor or lens fitter to make sure the lens fits properly. If your symptoms don’t go away, again, seek medical attention promptly. Don’t wait for a problem to become serious. When in doubt, find out what the problem is; some problems are serious, and some aren’t, but you won’t know unless you find out.

Some Questions You May Have about Contact Lenses

Can I wear contact lenses if I have astigmatism?

Sure. Statistically, about 40 percent of potential contact lens wearers could benefit from correcting astigmatism with contact lenses. If you’ve read chapter 2, you know that astigmatism is considered a “refractive error,” like nearsightedness or farsightedness. In a perfect eye, light enters through the cornea at the front of the eye and is focused to a precise point on the retina at the back of the eye. But with astigmatism, this focusing is skewed. Instead of being focused to a sharp point of light onto the retina, the light gets stretched out almost into a line; as a result, your view of the world is stretched in one direction and blurred. Eye doctors compensate for your astigmatism by prescribing lenses that have the opposite curvature of your eye; these lenses even out, or counterbalance, the way your eyes focus light. Note: Astigmatism does not reflect the health of your eye and should not be considered an impediment to contact lens wear.

The original hard lenses could correct mild to mod-

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erate degrees of astigmatism, but they weren’t too helpful for people with more significant astigmatism. What a difference a few years makes! Today highly precise RGP lenses, made by computer-driven lathes, can correct any degree of astigmatism.

The early soft contacts couldn’t do much to correct astigmatism. By 1980, as technology improved, several soft-lens designs incorporated corrections for astigmatism. And today many lens designs do a fine job of correcting astigmatism. However, there are still some practitioners out there who tell patients that they can’t wear contact lenses because they have astigmatism. This is not true. If you’ve been told that astigmatism prevents you from wearing contact lenses, take your business to a more enlightened establishment.

Am I too old to wear contact lenses?

Not unless you think you are. There’s no age limit on wearing contacts; plenty of patients enjoy their contact lenses well into their nineties. Actually, the only real limiting factor is the state of your general health. Arthritis can make it more difficult to insert and remove lenses, for instance. Dry eyes are more prevalent as we get older and can make lens wearing difficult—but certainly not impossible. Certain diseases (thyroid disease, collagen vascular disease, corneal dystrophies) and some medications (hormone replacement therapy and diuretics, for example) can cause problems for contact lens wear. But by all means, if you’re interested in contacts, talk to your eye doctor!

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How can I see to clean my lenses more easily, once they’re removed?

Place your lenses in a temporary case, put on your glasses, and then clean your contacts.

What happens if I leave my contacts out of their case and they dry out?

A soft contact lens will shrink considerably when it gets dry; it will also become brittle and fragile. But if you place the lens—gently—in a case with some saline, the lens will immediately start soaking up moisture like a sponge. It will probably take a good soak of at least thirty to sixty minutes before the lens is fully hydrated. Then, just clean and disinfect the lens again before you put it in.

With RGP contacts, drying causes no damage to the lens itself. However, these lenses have a surface treatment to make the lens surface more “wettable” (which helps your tears coat the lens surface evenly every time you blink). When an RGP lens gets dried out, this temporarily interferes with the “wettability,” and you’ll need to soak the lens for about four hours to replenish it. If you try to insert the dried-out lens right away, before it’s had time to recover, it will “soak” anyway—in your eye—and will feel dry and uncomfortable for those four hours until it’s finally refreshed.

How long do lenses last?

Generally, soft contacts that are neither disposable nor frequent-replacement lenses last from a year to eighteen