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

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or not see as well as you could, it doesn’t hurt your eyes not to wear glasses, and it is ultimately your decision.

External Examination

After vision and refraction comes the external exam- ination—what your doctor can learn simply by looking at your eyes without any specialized instruments. We may not write all of the observations down, or may do so very briskly, but we do pay attention to the following:

•The appearance and symmetry of the face

•The skin of the eyelids

•The edges of the lids and the lashes

•The position of the lids, and how well they open and close

•The clarity and shininess of the cornea, the irises, and the pupils, and their reaction to light

•The color, texture, and moisture of the conjunctiva (the slippery membrane on the front surface of the eye)

•The position, movements, and coordination of the eyes

This external exam can be done quickly. If there’s anything abnormal-looking or anything that needs to be looked at more carefully and in more detail, we generally notice it during the exam, even if we don’t always comment on it. If you think that your doctor missed something, or if you have a particular concern, by all means, ask! If, for example, you say, “What did you think of the black spot on my right eye?” your doctor may need to take another look—but more likely he or she has already formed an opinion about it.

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Pupillary Testing

The pupil is the black area of the eye, the part that is surrounded by color (the iris). All images must pass through the pupil before they are processed by the retina and perceived by the brain. The pupil, just like the aperture of a camera, opens and closes in response to light. In bright light the pupil gets small. In dim light it opens wide to allow more light to the back of the eye, to enhance the visual image. The shape and symmetry (or asymmetry) of your pupils and the way they react to light can give your doctor a lot of information about how you are seeing. Since the nerves that control pupil function have a relatively long course, including a circuitous route through the neck, abnormal pupil function can also provide clues about disease and other problems taking place elsewhere in your body, such as tumors, aneurysms, and vascular disease.

Examination of Important Structures within the Eye

Next, your doctor will examine your eyes with a slit lamp—a microscope with magnification of ten times (10x) to forty times (40x) or even higher. This lamp has a light source that can be used either to provide illumination or to produce a thin, controlled sheet of light. The intense line of light produced by this “slit” can illuminate a thin section of the cornea, the anterior chamber, or the lens. (For a look at these parts of the eye, see chapter 1.) These important structures of the eye are relatively

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transparent, so, like someone peering through a windowpane, we can look through one of them to focus on another. The slit lamp can also magnify and illuminate the iris, the conjunctiva, and the lids. With special stains and color filters, the slit lamp can reveal abnormalities of the cornea and conjunctiva from injuries or infections, or it can point out a deficiency of lubricating tears. With additional optics the slit lamp can also be used to examine the vitreous and retina.

Measurement of Intraocular Pressure

The measurement of intraocular pressure (pressure within the eye) is a routine part of the exam for adults, and often for younger patients as well. To measure intraocular pressure, the doctor must use a specially calibrated device. Several instruments have been designed for measuring intraocular pressure. Some use weights and look like small food scales, and others shoot a puff of air at the eye. The most commonly used instrument, however, is the applanation tonometer, which is mounted on the slit lamp. (This tool can swing out of the way when the slit lamp is being used to look at the eye.) Before using the applanation tonometer, the doctor will put a local anesthetic in the eye, as well as a dye called fluorescein, either separately or together. (These may sting briefly.)

When a cobalt blue filter is put on the light source, the fluorescein glows (or “fluoresces”) a bright, otherworldly green. The doctor or technician looks through the tonometer and turns a dial until the tonometer tip flat-

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tens a given amount of corneal surface. The amount of pressure in the eye is calculated using the relationship between (1) the force required to flatten the cornea and

(2) the area of cornea flattened. During this process the smooth plastic tonometer actually touches the front of the cornea, but the local anesthetic keeps the patient from feeling any discomfort. Finally, the doctor reads the dial of the applanation tonometer to find out how hard the tonometer had to work to flatten the cornea. This reading, the intraocular pressure, is registered in millimeters of mercury. The tonometer is an extremely useful instrument that makes it easy for ophthalmologists and optometrists to measure pressure within the eye.

Examination of the Retina

The slit lamp can also be used to illuminate the retina, but most doctors prefer an ophthalmoscope for this important part of the examination. There are two basic varieties. The direct ophthalmoscope is a hand-held instrument; the doctor holds it up to his or her own eye and then shines the light into the patient’s eye. The indirect ophthalmoscope looks like the classic miner’s lamp, with the light fastened to a headband. This light shines through a lens, held by the doctor in front of the patient’s eye. The lens focuses the light reflected back out of the patient’s eye into an optical image. The indirect ophthalmoscope can explore a larger area of retina, allowing the doctor to see farther into the peripheral retina, and in three dimensions. Ophthalmoscopes can reveal most abnormalities of the retina; in addition, they’re used to

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examine the optic nerve, the vitreous, and the blood vessels of the retina. (For a description of these structures, see figure 1.5.)

The retina is best viewed through a dilated pupil. Pupils are dilated by instilling dilating drops (see Appendix) into the patient’s eyes and waiting fifteen to thirty minutes for the drops to be fully effective. (In people whose irises are a dark color, this may take longer.) These drops affect each person differently and last longer for some people than for others, depending on the type and strength of the drop or drops used. In general, pupil dilation will also be accompanied by a loss of accommodation, or the ability to see things up close. Most people maintain adequate distance vision, so they can see to drive home; but they will need to wear their distance glasses if they usually do so for driving. Sunglasses may also be necessary, especially on a bright day.

If you are uncertain about how dilating drops will affect you, the safest approach is to bring someone along with you to the eye examination—a designated driver. Usually the effects of the dilating eye drops wear off after a few hours, but in very rare instances these effects can take days to go away. Eye doctors must be very careful when using drops to dilate the pupils, since these drops can bring on acute closed-angle glaucoma in people with a narrow anterior chamber angle (see chapter 8).

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Additional Tests You May Need

What we’ve just covered are the basic parts of the standard eye examination: your medical history, the measurement of visual acuity, refraction, the external examination, examination of the internal structures, the measurement of intraocular pressure, and the retinal exam. Remember the beginning of this chapter, where we said that an eye exam could be fairly simple or more involved? Well, of all the many tests that can be done on eyes, some, like these, are done always and are considered routine.

Some additional tests, however, are done often but not always; many others are done only occasionally, unless the doctor has a special interest in, or specializes in diagnosing and treating, a specific type of problem.

This second group of tests—those that are done often but not always—includes measurement of visual fields, gonioscopy, exophthalmometry, and tests of tearing, of eye coordination, and of color vision. Let’s go over these.

Measurement of Visual Fields

Your visual field is pretty much what it sounds like: the total area, up, down, and sideways, that you can see with one eye. It is also the drawing or diagram that represents what you can see. A visual field drawing indicates what size or color object you can see, at what distance from straight ahead, diagramed as odd-shaped circles. To get a better idea of how this works, see figure 3.3. People see

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Image not available.

Fig. 3.4. Amsler grid

best straight ahead, with the macula, and then less well the farther the object is from “fixation,” or dead center— in other words, at the outer edges of our visual field, or what we can glimpse from “the corner of the eye.”

Like nearly everything else in our high-tech world, visual field testing has become much more complicated and expensive over the last decade or so—but also better, in this case with the use of automated, computerized “perimeters,” or visual-field-testing machines. These usually measure how high or how bright a light has to be

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in order for you to see it at a given position. Some of the more elaborate tests, involving hundreds of spots of light, can be tiring, but most are reasonably brief. Your doctor can also measure your visual field by having you observe a light at a certain spot getting brighter, or a light of fixed size moving in from the periphery toward your center of vision.

As a means of quick screening, to see whether someone’s visual field warrants further study, a simpler test can be done. In this test your eye doctor might ask you to focus on his or her face and then would note at what point you’re able to see a pencil or finger coming into view from below, above, and the sides. This type of “confrontation” field is a good way of determining whether your visual fields are normal or not. However, tests of this type are useless for detecting glaucoma; and because such tests do not accurately diagram any abnormality, they can’t tell us anything about whether a specific condition is getting worse.

Another, specialized type of visual field test, called an Amsler grid, is a square with a pattern of small squares (like a piece of graph paper) and a dot in the middle (see figure 3.4). It was designed by Professor Marc Amsler as a rapid self-test to detect changes in the central 20 degrees of the visual field. The test is particularly helpful at identifying diseases of the macula and optic nerve that affect vision.

Here’s how it works: First, you’ll be asked to focus your gaze (using one eye at a time) on the dot in the center of