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

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the square. Now, some questions. How does the pattern of small squares look to you? Does any part of it seem to be missing, distorted, blurred, or warped? Which part? Distortion is an important warning sign; in most cases the distortion a patient sees matches a problem in the corresponding area of the retina.

Amsler grids can be administered at home as self-tests by patients who are considered likely to develop retinal problems. (Particularly at risk, for instance, are patients who have already had retinal trouble in one eye. For a more detailed discussion of retinal problems, see chapters 9 and 15.) Here’s how to use the grid at home: Post it someplace where you can easily see it every day—some hard-to-miss spot like the refrigerator door or bathroom mirror. It’s designed to be looked at, in modest light, from a distance of about a foot. If you wear glasses, contacts, or bifocals for reading, use them for this test, too.

It’s simple to use. First, cover one eye and study the grid with your other eye. Look straight ahead at the central dot and nowhere else!

Now, answer these questions:

•Can you see the dot in the center?

•Can you see all four corners of the grid?

•Are all the small squares the same size?

•Are all of the lines straight, or are some of the lines wavy? Are any parts of the graph missing?

•Is there any movement? Any color aberration?

Now, repeat the test using the other eye. If you notice any changes—distortion, blurring, discoloration, or a

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complete absence of any part of the grid—contact your eye doctor immediately for an examination. If you’re at high risk for macular or optic nerve problems—if you have advanced macular degeneration, for example—you should test yourself daily. Other people should consult their eye care specialist for a recommendation about how often they should perform this test.

Gonioscopy

A gonioscope, or gonioprism, is a device, about the size and shape of a thimble, that fits against the cornea. With the help of an anesthetic eye drop and a gooey drop to keep out air bubbles, the doctor can use this instrument to detect some kinds of glaucoma. An angled mirror inside the gonioscope—similar to the one your dentist uses—allows the slit lamp to focus “around a corner” into the space where the back of the cornea meets the front of the iris. (For more on these parts of the eye, see chapter 1.) This space is called the angle of the anterior chamber, and the angle itself is important: a narrow chamber angle may signal glaucoma.

Exophthalmometry

An exophthalmometer—one of our real tongue twisters—is a ruler with two arms that rest on the outer rims of the patient’s orbits. Its angled mirrors enable the doctor to check, basically, whether the eye sticks out, or projects, farther than it should. The exophthalmometer is used most often to measure the amount of abnormal eye protrusion (also known as exophthalmos) associated

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with thyroid disease, but it is also used to monitor other causes of protrusion of the eyes.

Tests of Tearing

Do you have dry eyes? (The problem of dry eyes is discussed in chapter 13.) Would artificial tears help you? There are several tests available to help us answer these questions. One of these tests for diagnosing “deficiency of lubricating tears”—in other words, dry eyes—involves using paper strips to measure tear production, often along with an anesthetic drop (which helps decrease reflex tear production during the test). This is called the Schirmer test. One end of each paper strip is bent to fit inside the lower lid; the rest of the strip hangs down over the cheek. The amount of the strip wetted by tears is measured after two to five minutes. Note: There’s a surprising amount of disagreement among ophthalmologists about the accuracy and usefulness of the paper strip test.

The rose bengal dye test provides another gauge of whether the patient has dry eyes and will find artificial tears useful. In this test a drop of dye is put inside the lower lid. The dye usually stings and is usually applied after application of anesthesia. If someone has a tearing deficiency, the dye leaves tiny pink-stained dots on the cornea and conjunctiva. The dots are visible with the slit lamp and represent areas where the corneal epithelial cells are either devitalized or missing. The doctor can tell by the patterns of dye staining whether there’s a problem with dry eyes. (Note: While these dots are not perma-

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nent, there is in this test a possibility of spilling the dye on clothing, where it probably is permanent, so be careful not to rub your eyes immediately after the test, and make sure your doctor carefully rinses this dye from your eyes before sending you home.)

Tests of Eye Coordination

Most people see a little better with both eyes than with either eye alone. When this seems not to be the case, the problem usually has to do with the coordination of the two eyes—how well they work together. The brain uses a highly sophisticated feedback system to keep our eyes coordinated and avoid double vision. This system can correct large amounts of horizontal drift, quite small amounts of vertical drift, and almost no amount of rotational drift (see chapters 1 and 2).

As with any complicated system, some problems are more fixable than others. A few examples: If it’s an eye muscle problem making someone see objects as level with one eye but tilted with the other eye, about all we can do is patch one eye and hope the other one will get better; or we can perform eye muscle surgery in an attempt to level the tilted eye. Much more common—and much more easily correctable—are small but annoying amounts of horizontal or vertical muscle imbalance. Such muscle imbalances are usually not detectable with an external exam, but we can distinguish them with tests such as the cover-uncover test, the alternate cover test, and a red glass test. Here’s how the red glass test works: When you look at a light, your brain knows you’re seeing just

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one light, and it works hard (but not cheerfully) to keep single vision. If, however, you hold a red glass in front of one eye, the brain relaxes its effort, and the white image seen by one eye separates from the red image seen by the other eye. The amount of this separation can be measured by the amount of prism necessary to line the two images up together. A prism lens can bend light in predictable amounts to compensate for eyes that cannot line up visual images by themselves. Putting a portion of the calculated amount of prism into the patient’s glasses is often very helpful in solving such problems of muscle imbalance.

Tests of Color Vision

Tests of color vision are mainly used to diagnose inherited genetic defects of color vision. Such testing is rarely done in adults but may be used in diagnosing some optic nerve and retinal problems completely unrelated to inherited color blindness (for example, in checking for possible toxicity—in other words, too much of a drug in the system—from Plaquenil, a drug used to treat rheumatoid arthritis). These tests consist of asking the patient to identify colored numbers lying in a field of another color, or arranging various color samples in a specified order (as at the paint store, when we are trying to find the perfect shade of blue for the living room walls). If someone has trouble distinguishing different colors, the tests will reveal the problem and identify the problem range—red and green, for example—in the color spectrum.

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Other, Less Common, Tests

Still other diagnostic tests, used much less commonly, are retinal photography and retinal fluorescein angiography. As with angiography of the heart, this is a series of pictures of the blood vessels—in this case, those within the retina—taken using a luminous dye. Pictures are taken as this dye, injected into the vein of the arm, moves through the arteries, capillaries, and veins of the eye. These pictures can reveal specific problems inside the eye such as age-related macular degeneration and diabetic retinopathy.

Another test occasionally needed is an ultrasound examination of the eye. This painless, noninvasive test—just like the ultrasound imaging commonly used in preg- nancy—creates a picture with sound waves. When used in the eye, it can detect abnormalities such as tumors or retinal detachments (when, for example, bleeding in the eye or a dense cataract makes them impossible to detect during an optical examination). Examinations of the eyes by other imaging means, including X-ray, computerized tomography (CT) scans, or magnetic resonance imaging (MRI), can also be helpful in some cases. If one of these tests is necessary, it will usually be performed by a subspecialist, preferably someone recommended by your ophthalmologist or internist.

In summary: Most eye exams are quick and simple; a few are long and complicated. Knowing which tests to do under specific circumstances requires the doctor to be

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well educated and trained, to listen well, and to consider carefully what’s best for the patient.

Some Questions You May Have about Eye Exams

I’m getting my eyes dilated today. Will I be able to drive myself home?

Probably. Most people are able to drive after getting their eyes dilated, but everyone reacts differently.

Dilating drops work by enlarging your pupils and relaxing your accommodation (see chapter 2). If you’re nearsighted, or if you don’t normally wear glasses, you may have trouble with bright sunlight and glare, especially if there’s snow on the ground. (If you need them, your doctor will probably provide a pair of plastic sunglasses to help cut the glare.) Also, this temporary loss of accommodation usually makes such up-close work as reading a bit more challenging. (If you need to read soon after getting your eyes dilated, it might help to remove your glasses or contacts.) But you probably won’t have trouble driving; the eye drops shouldn’t hamper your distance vision.

If you’re farsighted, however, you may have some trouble temporarily—just for an hour or two, depending on the particular eye drops and their strength. Because the drops affect the eye’s ability to accommodate, and your eyes work by using accommodation to see things far away, it’s possible that your distance vision could be disrupted for a short while.

If you’re concerned about your ability to drive home,

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discuss this beforehand with your eye doctor. This part of the exam may not be necessary, or you may be able to postpone it to another visit. Or you could bring a “designated driver” to help you get home.

My husband’s doctor said that he’s legally blind. What does that mean?

Legal blindness is a confusing term. It’s not so much a particular diagnosis as a purely legal definition that enables sight-impaired people to qualify for helpful serv- ices—many of which are free—including “low-vision” assistance, occupational therapy, and tax benefits.

Every state has its own guidelines for legal blindness. To learn more about these, and to explore the range of services for which you may be eligible, call your state’s Department of Social Services.

According to federal guidelines, you’re “partially blind” if your vision in the better eye, when best corrected with glasses or contact lenses, is 20/200 or worse. For example, if you have macular degeneration with a visual acuity of 20/200 in one eye and 20/400 in the other, this would apply to you. (If, however, your vision is terrible in both eyes without glasses but you see 20/20 with glasses, then you’d be ineligible.) If your vision is better than 20/200 but your field of vision (see above) is severely limited—as if, with no peripheral vision, you were constantly looking at the world through a tube or tun- nel—you may also be considered legally blind.

If your spouse is classified as legally blind, they may be eligible to receive an extra deduction on their federal in-

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come taxes. To qualify for a legal-blindness deduction on their federal income taxes, they’ll need to attach to their tax return a written statement from their eye doctor, indicating their visual acuity or field of vision. (They should be sure to keep a copy for their own records as well.) If their condition will never improve, they can file an eye doctor’s statement to this effect with the Internal Revenue Service. This will be on permanent record for all future tax returns.

Are headaches often due to eye problems?

Not as often as you might think. Headaches (see chapter 18) come in many forms. Some are mild, some severe; some are fleeting, while others linger for days. Some go away with a couple of aspirin; others require much stronger, prescription medication. But very few of these are actually caused by eye problems. Discomfort around the eyes can be related to eyestrain and the need for glasses, but this usually results from using your eyes for long periods—especially for close work—and is often relieved by a simple change in activity or by an over-the- counter pain reliever.

Note: If you’re having frequent or severe headaches, see your eye doctor and your family physician or internist. They will want to rule out other health problems. Other factors that can cause headaches include tension, allergies, sinusitis, and temporal or giant cell arteritis (see chapters 17 and 18); migraines and other systemic disorders may also need to be considered.

4

All about Eyeglasses

Many of us are all too familiar with the concept of a “vision correction”—usually eyeglasses or contact lenses, but increasingly refractive surgery as well—because we’ve dealt with less-than-perfect eyesight for years. But there are just as many first-timers out there who are new to all this: adults, often in their forties and fifties, who suddenly find themselves needing extra help to see better. This prospect and all that it might represent, including the inevitability of growing older, can be, at the very least, unsettling.

But take heart. Your timing couldn’t be better! Never before has there been such a wide and remarkable range of options, including choices that might have seemed like science fiction even twenty years ago.

Major technological advances in the way eyeglasses and contacts are manufactured now allow us to see better with fewer compromises to lifestyle and appearance. Today surgery is a possibility for correcting some vision