Ординатура / Офтальмология / Английские материалы / The Eye Book A Complete Guide to Eye Disorders and Health_Cassel, Billig, Randall_2001
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months. This is based on an average wearing day of about twelve to fourteen hours, seven days a week. But if you wear your lenses longer—eighteen hours a day, for example—they might wear out sooner, in as little as nine months to a year. Even if you take the most meticulous care imaginable—if you’re an eye doctor’s dream, in fact—the material will still wear out. Several things contribute to this. Just rubbing your lenses, the act itself, tends to break down the lens surface over time. (However, if you don’t scrub your lenses they’ll wear out even sooner, because the coatings that accumulate will eventually form permanent, impossible-to-clean deposits on the lenses.) Every time you blink, you wear down the lens a little. Eventually the surface of the lens begins to erode and become dimpled, like the surface of a golf ball. Deposits start to form in those dimples, and they bind to the lens so tenaciously that they can’t be cleaned off.
The life span of disposable lenses is based on your wearing schedule; they should be replaced every one to fourteen days. By the end of their cycle, nearly all of these lenses show signs of wear, so even if your lenses feel fine, they should be replaced. If you wait until the lenses hurt before replacing them, you may wind up with one or more of the problems these types of lenses were designed to avoid (such as giant papillary conjunctivitis and corneal oxygen deprivation).
Frequent-replacement lenses are generally meant to last two weeks to three months, depending on your particular schedule and the lens material.
For RGP lenses, the life span of the lens depends very
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much on how you take care of them. If, with all good intentions, you rigorously clean your lenses between your thumb and forefinger, your lenses may actually warp within a few cleanings. If you’re a careful cleaner (see above for tips on cleaning), these lenses can last for years. Your doctor or lens technician can even prolong the life of your lenses by polishing them to remove any fine surface scratches that may accumulate over time. Polishing can also remove any rough spots on the lens edge, which can cause irritation.
There has been some research to support the theory that RGP lenses eventually wear out like a soft lens; electron micrograph photos have shown tiny surface disruptions on aging RGP lenses. However, because these photos show a lens magnified up to one million times, there’s some dispute as to whether these irregularities are clinically significant, and whether they actually reduce the life of your lenses.
What are those white bumps that I see on my soft contact lenses?
They’re the deposits that inevitably form on a wornout lens, a conglomeration of mucins, oils, debris, and protein. Every time you blink, you contribute a thin layer to these evolving deposits, like an oyster working on a pearl. Eventually the deposits get larger and larger, resulting in the sizable white bump you’re seeing. And this means it’s time to replace the lens.
How do I care for my lenses if I don’t wear them every day?
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If you use a chemical disinfection system with your soft lenses, such solutions can usually maintain a lens for long-term storage of up to two weeks, depending on the product. If you use a heat system, you’ll need to find a saline solution with sufficient preservative potential to keep your lens sterile after it has been heated. The problem here is that most saline solutions lack adequate preservatives to keep a lens sterile for long-term stor- age—which opens the door for potential bacterial and fungal growth on the lenses and in the lens case. Thus, heat disinfection is not terribly practical for the occasional lens wearer. Hydrogen peroxide solutions can maintain your soft contacts for much longer storage pe- riods—so long as there is nothing to neutralize the hydrogen peroxide. (Which means that you’d need to remove the neutralization mechanism before storing your lenses.)
For soft-lens wearers, one-day disposable lenses address this dilemma nicely. You can wear the lens once and throw it away, and store the rest of your lenses in a cool, dry place until you’re ready for them.
With RGP lenses, most soaking solutions are fine for storage of up to one to two weeks. If you’re storing an old pair to keep as an emergency backup for your current lenses, you’ll want to store the lenses dry after a thorough cleaning, to ensure that the lenses don’t get contaminated by sitting around in old solution. Be sure to soak your lenses for at least four hours before again trying to wear them.
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If I wear bifocal glasses, can I still wear contacts?
Absolutely. The primary problem here is that you’re dealing with at least two different glasses prescriptions: your distance prescription doesn’t work for reading, and you can’t see far away with your reading prescription. Also, some people who wear bifocals need intermediatedistance vision (generally from two to four feet) prescriptions. (In glasses, this is handled either with progressive addition lenses or with trifocals. For more on this, see chapter 4.)
Any decision that you and your doctor or lens specialist make together will be a compromise; what you need to decide is whether that compromise is more suitable to your needs than the compromise of wearing glasses alone.
A good option—the one that probably provides the best vision—is to use contact lenses for your distance vision and to wear reading glasses over the contact lenses. If you have demanding visual needs, or if your work requires some eye protection at a close distance—if you’re a dentist or auto mechanic, for instance—then this can be an excellent way to go. If you need trifocals, you can have your reading glasses made in a format that addresses both intermediate and close-up visual needs. (Of course the compromise here is that you’ll still need to put on glasses for part of the day.)
Another option sounds like a special effect in the movies. It’s called monovision: using one eye for distance vision and the other for seeing close up (generally, the
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distance contact goes in your dominant eye). This is not as taxing as it sounds, and it can be achieved with any kind of contact lens. Even if, for instance, you need cus- tom-made lenses to correct an unusual astigmatism, the lenses can still be modified so that one eye sees distance and the other reads. (A prerequisite for monovision is that both of your eyes must have excellent vision, and each must work properly by itself.)
Since its inception more than thirty years ago, monovision has been a controversial idea. However, recent studies have shown that it’s safe, in that it doesn’t affect how you use your eyes together. Even people who have worn monovision contacts for years still have good binocular vision (using both eyes together) when they wear glasses.
Of concern to many patients who wear monovision contacts is a loss of depth perception. At a long distance, you perceive depth based on information that can be provided to either eye and is not dependent on how you use your eyes together. For example, when you see a car parked in front of a building, you know that the building is farther away than the car. You can see this with either eye by itself, just the same as you would with both eyes together; you don’t see the car as being in the building when you close one eye. Other clues to depth are relative differences in shadowing, shading, coloring, and contrast.
Recently, researchers at the University of California School of Optometry in Berkeley studied how well contact lens wearers who need bifocals functioned with var-
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ious types of lenses, in terms of hand-eye coordination and depth perception. The study found that patients who wore contacts with reading glasses could perform up-close tasks best, and that patients who wore monovision contacts did exceptionally well and better than those who wore soft bifocal contacts (another option; see below).
A major advantage to monovision is that you can view up-close objects from any angle. Say you go to the grocery store and you’re wearing bifocal glasses. You want to read a product label that’s at or above eye level. Well, you probably can’t without first taking the product off the shelf and holding it at the appropriate angle. With monovision, though, you just look up and read the label, just as you did before you had bifocals.
The compromise with monovision is that your vision is generally not as sharp as it is with your glasses. You lose what’s referred to as binocular enhancement, the enhanced visual image you see when both eyes work together. For the most part this is a concern only under specific circumstances, such as driving at night—in which case you can resolve the problem by using driving glasses. (You wear them over your monovision contacts to offset the near-vision contact lens and bring that eye back to a distance prescription. The other side is a nonprescription lens.)
Also, with monovision there can be a compromise to intermediate vision, if you’re accustomed to wearing trifocals or progressive addition bifocals. Some people resolve this by replacing the near contact lens with a pro-
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gressive addition bifocal contact lens that will provide good vision close up but will extend your working distance to allow for good intermediate vision.
The last option is bifocal contact lenses. These are designed either as simultaneous-vision or translating-vi- sion lenses. A simultaneous-vision lens has both distance and near optics that focus light into the eye at the same time: when you’re looking at a distance, your brain learns to ignore visual information from the up-close part of the contact lens, and vice versa. Simultaneous-vision designs are accomplished either by creating different distance and near zones within the lens or by varying the power of the lens from the center to the edge. (This is akin to the way progressive bifocal eyeglasses vary the power from top to bottom.) Many of these lens designs provide 20/20 vision, but the quality of that vision may be reduced from the loss of contrast, and the things you see might not seem sharp or well defined. One advantage, as with monovision contacts, is that you can read up-close objects at any angle. The compromise is that although you use both eyes together, the vision is still not always as good as it is with your glasses.
A translating bifocal contact lens works like traditional bifocal glasses: there’s a tiny line that separates the distance prescription at the top from the reading segment at the bottom. (A built-in stabilization system makes sure that the lens always sits the right way in your eye so that the distance part is always at the top.) When you glance down, the lens should move, or “translate,” up, placing the reading area in front of your pupil so that
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you can see up close. Soft translating bifocal contact lenses tend not to work well, because these lenses generally can’t move enough to bring the near optics where you want them, in front of your pupil.
The best of these designs are made in RGP materials; they can provide excellent vision that can match or even surpass your glasses. However, they also have the same limitations as standard bifocal glasses. When you glance down at the floor, it’s blurry; to see anything clearly up close, you have to hold the object down at a certain angle, just as you would with glasses. So if you work at a computer and your monitor sits at eye level, for example, you won’t be able to use the near optics of your contact lens to see the computer monitor. If you can’t adjust your work area, then this lens design might prove more of a hassle than a help.
Why does my lens just stick to my finger whenever I try to put it in? Why won’t it stay on my eye?
No matter what kind of contact lens you have, when you insert it, the inside surface—the side that rests on your eye—is wet enough to “pull” the lens onto your eye. This works because fluid is naturally drawn to fluid; a wet lens naturally wants to stick to your wet eye. But if your finger is too wet, there’s too much “fluid attraction,” and the lens sticks to your finger instead of your eye.
When you’re putting in soft contacts, make sure that only the bottom of the lens (not the edge) is resting on your finger. Next, open your eyelids wide enough to provide a clear shot at your eye, so that the lens won’t be
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waylaid by your lashes. Don’t poke your eye, and don’t press so hard that you just push the lens back onto your finger. Simply get the lens within striking distance—close enough that it can “work off ” of your finger and onto your eye. If you can’t get the hang of it, go back to your eye doctor or lens fitter for a refresher lesson. After all, the contact can’t help you much if it stays on your finger!
How can I tell if my contact lens is inside out?
It’s almost impossible to turn an RGP lens inside out. However, it can be done. You’ll know something’s not right, because your lens will look almost flat, and if you can put it on your eye, it probably won’t stay on. If you manage to turn the lens right side out again, it will most likely be too warped to wear, and you’ll need to get a new one.
If you have soft contacts and aren’t sure if a lens is inside out, look at the lens, invert it, and look at it again. (Often it’s difficult to tell by just looking at the lens one way; by comparing both views, you’ll have a more accurate assessment.) If the lens is as it should be, right side out, the edges will point up and the lens will form a bowl. If it’s inside out, the edges will point more out to the sides than up to the skies, and the lens will appear “flared,” like a champagne glass.
A second way to tell is to place the lens in the crease of your palm and gently cup your hand so that it starts to fold the lens. If the edges roll into each other, like a taco shell or clam shell, the lens is right side out. If the edges
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start to fold back, away from the center, the lens is inside out.
If you place an inside-out soft contact lens on your eye, your vision might still be clear. However, you will feel uncomfortable, and you’ll probably feel that the lens is going to fall out. If you have this sensation, try removing the lens, inverting it, rinsing with saline, and reinserting it. If the lens feels fine, you’ve solved the problem. If it feels worse, it’s likely that you had inserted the lens right side out the first time, and that either you had some debris on the lens that altered the fit or there’s a nick or tear in the lens. If you can’t get it to fit so that it feels right, let your eye doctor or lens fitter take a look at it.
Can I wear my contacts if I have hay fever? Can I use allergy eye drops with my contacts?
It depends on your symptoms. If hay fever for you means irritated, dry, and itchy eyes, then you might not be able to wear contact lenses during allergy season; the lenses might make your eyes feel drier and increase your itching. Also, some allergy medications can make the problem worse by drying out your eyes even more, making contact lenses uncomfortable.
However, if you get relief from one of the many allergy eye drops available, you might still be able to wear your contact lenses during allergy season. Note: These drops should not be inserted while your contact lenses are in your eyes. Soft contacts, especially, will soak up the drops