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

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(Imagine the difference in texture between watercolor and oil-based paint.) As a result, the cornea tends to dry more quickly.

One of the most common eye diseases to obstruct lipid production by the Meibomian glands is blepharitis, an infection of the eyelid (see chapter 10). When the eyelid becomes infected, bacteria (and the immune reaction they trigger) cause the Meibomian glands to clog and shut down. Again, the result is a more watery (and less oily) product: tears that evaporate much more quickly from the eye. Even worse, as these lipid-lacking tears evaporate, they leave behind a greater-than-normal concentration of salt, and salt burns the eyes.

Another common cause of dry eye from lack of lipids is sleeping with your eyes open (nocturnal lagophthalmos). Sleep is the body’s great restorer, a chance for everything, including eye moisture, to be replenished. If you don’t close your eyes fully when you sleep, exposed parts of your eye tend to dry out. Symptoms are usually at their worst when you wake up, and get better during the day as normal blinking returns moisture to the eye. This is a fairly easy-to-treat problem; often, simply applying an artificial tear ointment before bedtime is enough to keep the eye moist overnight. (Nocturnal lagophthalmos is also a common problem for people with Bell’s palsy; the lid of the disabled eye doesn’t close at night, and this makes the already dry eye feel even worse. But taping the eye closed at night, along with the use of artificial tear ointments, can help replenish eye moisture.)

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Distribution Problems

With tears as with any complicated manufacturing system, the breakdown may come not in quality control or production but in shipping or distribution. Sometimes the tears themselves are just fine, and they’re made in adequate amounts, but the eye itself can’t get them where they need to go.

Irregularities on the surface of eyelids or corneas, for instance, can cause dryness even if tear production is adequate. If the eyelids are scarred significantly—a problem in chronic blepharitis—the lid can’t distribute tears evenly across the surface of the cornea; think of faulty wiper blades trying to sweep a car’s windshield. Similarly, if the cornea is scarred, the lid can’t do a good job of spreading tears. In either case, the tear-deprived surface of the cornea becomes parched.

Growing older can also cause changes in the musculature and shape of our eyelids, occasionally causing them to sag or turn outward (ectropion) or inward (entropion; see chapter 10). These problems too disrupt how tears are spread across the eye, and how they flow out of the eye. Often, when this happens, people experience symptoms of dryness. A person may also have tears that stream down his or her face. (This may sound like a flatout contradiction of a diagnosis of dry eyes: after all, how can your eyes be dry when they’re literally overflowing with tears?)

Finally, some people just don’t do a good job of blinking; consequently, tears don’t get spread across the eye as

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they should. With each complete blink, the upper lid should meet the lower lid. Partial blinking leaves the lower portion of the cornea constantly exposed and increases dryness over the course of the day.

Diagnosing Dry Eyes

The first step in diagnosing dry eyes is to measure both the quantity and the quality of your tears. Your eye doctor will probably begin a careful examination of your eyes with a slit lamp biomicroscope, a microscope that gives a three-dimensional magnified view of the front surface of your eye. The doctor will look for any irregularity on the surface of your cornea, any abnormality in the position and function of your eyelids, and any dysfunction of your Meibomian glands. The doctor may also use special stains—two types of dyes are used, fluorescein and rose bengal—to highlight damaged cells and dry spots on the surface of the cornea. (The principle here is similar to that behind those awful red dyes dentists sometimes use to illustrate where you’re not adequately brushing your teeth. In this case, areas of damage and dryness absorb the stains and pinpoint the trouble spots on your cornea.)

Next, your tears will be scrutinized for volume and quality. Are they relatively clean, or do they contain “ocular debris” (skin cells, airborne particles, and mucin strands)?

Are you blinking well? Your doctor will also check to make sure that your eyelids are adequately spreading tears across the surface of the eye.

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Tear volume can be measured with something called a Schirmer test. The description is worse than the actual test. “Schirmer strips” (sterile pieces of paper) are folded and hung over your lower eyelids. For five minutes they’ll soak up your tears; then your doctor will measure the saturated area of each strip to determine whether you’re making enough tears. Some doctors are convinced that the Schirmer test is very useful, while others question its value. We think that it actually does tell something useful about tear production.

Fluorescein dye, which sticks to the mucin layer of tears, may also be used to determine your “tear breakup time” (how well your tears maintain their integrity)—in other words, to find out whether your problem is an issue of tear quality. After putting a few drops of fluorescein in your eyes, your doctor will ask you to blink several times, to get an even distribution of your tears across the cornea. Next you’ll be asked not to blink, while your doctor observes and measures how long it takes before the tears evaporate and dry areas are observed on the cornea. The rose bengal test (described in chapter 3) is another test in which a dye placed in the eye can help doctors diagnose a dry eye.

For more specific tests, your doctor may need to send samples of tears or tissue (this is painless) from your eye to a laboratory. Tears can be tested for quantities of salt, electrolytes, and proteins to help pinpoint the cause of dryness, and conjunctival tissue can be biopsied to look for changes within the cell structure that may indicate the source of the problem.

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Treating Dry Eyes

Simply put, the basic goal in treating dry eyes is to keep the eye moist—in other words, to treat the symptoms, and not the cause. There are several ways to do this.

Tear Substitutes

Tear substitutes are used to rewet the ocular surface. Fortunately there are many good over-the-counter teardrops to choose from. Depending on why your eyes are dry, you’ll probably find that some tear supplements work better than others. Some people need a drop that “mimics” tears to add more quantity. Others need drops containing extra lubricants to enhance the mucin layer and improve tear quality.

If burning is a problem, you can find drops that are hypotonic (containing less salt than natural tears). If your problem is more severe and you need drops particularly often (several times an hour), you may prefer preservative-free tear supplements, which are often easier on the eye. Tear ointments are especially useful for people who wake up at night or in the morning with dry, gritty, irritated eyes. They are inserted in the eyes at bedtime.

Note: Be careful using drops designed to “get the red out” and improve the cosmetic appearance of your eyes.

These treat a different problem. Often these drops contain ocular decongestants and vasoconstrictors that shrink the dilated blood vessels that show up when your eyes are dry. These additional ingredients can affect mucin production, so although your eyes may look better, they’ll

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still feel dry. Also, as many of us have learned the hard way with similarly acting nasal sprays, constant use of vasoconstrictors can lead to a temporary “rebound” reaction, in which these blood vessels actually dilate more and your eye looks even redder than it did before you used the eye drop. If your eyes are red because they’re dry, appropriately rewetting them with an artificial tear supplement usually takes care of the redness as well.

Procedures to Fix Your Tear-Drainage System

If tear supplements don’t ease all your symptoms, your doctor may suggest methods of making more use of the tears you have, by keeping them in your eye longer.

One approach is to close the puncta (the eye’s “tear drain”) to slow or lessen drainage of tears into the nose. Remember, you’ve got two of these in each eye, one on the lower eyelid, one on the upper. Your doctor may want to close only the one on the lower lid to reduce the outflow of most of your tears, but leave the upper lid’s puncta open. One bonus here is that this procedure doesn’t have to be permanent; your puncta can be closed temporarily, as a test to see whether such treatment will help or not. Your doctor can close the puncta with collagen plugs, which will slowly dissolve over the next few days. (If the plugs work and the dryness improves, then you can talk about more permanent treatment.) If the collagen plugs don’t last long enough for you to measure the effectiveness of this approach to treatment, your doctor can use silicone plugs (which will close the puncta until they’re removed). Then, if you and your doctor de-

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that’s certainly one reason for tearing. When eye doctors use the term, we simply mean “making too many tears” —in other words, having watery eyes.

Ideally the eye maintains a delicate balance between tear production and drainage. To review briefly: Most tears are secreted by glands in the upper eyelid onto the cornea, where they act as the eye’s “window-washer” fluid, constantly bathing the cornea (see figure 13.2). They either evaporate or collect in the “gutter” created by the lower eyelid, called the inferior cul-de-sac. Blinking pumps the tears in this gutter ever downward toward the nose; first they drain through the puncta in each eyelid, into a common aqueduct to the nasolacrimal sac. From here tears flow into the nose and then to the back of the mouth, where they mix with saliva and are swallowed.

Many things can cause excess tearing. Most common are foreign particles (specks of dust, for instance) that get blown into the eye; the eye jump-starts its tear production in an attempt to wash out these invaders and cleanse itself. Eye infection, emotional stimuli (such as, literally, the “tear-jerker” movie), wind, smoke, and fumes—all of these can cause more tears to be made. Ironically, as mentioned above, even dryness in the eye can cause increased tearing.

But tearing can also result from poor drainage of tears from the eye—think of rain that pools in a blocked gutter. Sometimes irregularities in the shape of the eyelid can hamper tear drainage or hinder blinking (a critical means of keeping tears moving through the drainage

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system). A deformed punctal opening or blocked tear duct—this sometimes happens with aging—may also cause a buildup of tears. In this case, as a simple outpatient procedure, your doctor can dilate, probe, and irrigate or flush the nasolacrimal drainage system and reopen this passage. If this does not work, then thin silicone tubing can be used to dilate and reestablish the flow of tears through this system.

One important but often overlooked cause of teardraining problems is an infection in the nasolacrimal sac called dacryocystitis. Remember, tears drain into this sac before they pass downward into the nose and throat. Sometimes bacteria find their way here as well, and the resulting infection can be difficult to treat because the sac is located so deep within the tissues around the eye. The nasolacrimal sac is hard to reach with topical drops, and oral antibiotics are often needed to knock out the infection.

The biggest problem here, however, is that because of the often-elusive nature of such infections, they can go undiagnosed for months—leading to scarring of the nasolacrimal sac and chronic tearing problems. When this occurs it may be necessary to open the scarred sac surgically. (This procedure is known as a dacryocystorhinostomy, or DCR.) Patients with tearing difficulty due to dacryocystitis must weigh their degree of discomfort against the anxiety, inconvenience, and cost of undergoing surgery. You may decide that having too many tears isn’t so bad after all. As one patient points out, “It’s better than having a dry eye.”

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Some Questions You May Have about Dry Eyes

Sometimes my vision gets blurry, but I can clear it with a few blinks. What’s the problem?

If your eye is dry, the surface of your cornea can lose some of its smoothness. Dry patches form on the cornea, and this tends to blur vision in between blinks. But by blinking several times in a row—think of applying a roller of paint to a rough wall—you fill in those dry patches with tears and clear your vision. This problem is much improved too by artificial tear supplements, which help heal the dry patches and maintain more consistent vision.

Why do my eyes burn when I work at my computer?

You know that daze you feel sometimes when you stare at the computer for hours on end? You’re not imagining it; many of us really do go into a kind of trance after prolonged computer use. We blink less, for one thing. Then, with a lower tear supply, the moisture in our eyes starts evaporating. When this happens, the normal amount of salt in our tears builds up, becomes more concentrated, and starts burning. Using an artificial tear supplement that is hypotonic (containing less salt than natural tears) helps ease this symptom. (It may also help if you make an effort to blink more often while you’re working on the computer.)