Ординатура / Офтальмология / Английские материалы / The Eye Care Sourcebook_Lavine_2001

T H E E Y E C A R E S O U R C E B O O K

as they spread over the surface of the retina. The branches of the central retinal artery supply the blood for the inner layers of the retina. Abnormalities of the blood vessels caused by diabetes, high blood pressure, and other diseases can cause leakage of fluid and hemorrhage into the retina, which in some cases can blur vision. The retina is also subject to numerous other problems, including detachment, degeneration, infection, inflammation, injuries, and rarely tumors.

The Optic Nerve

The optic nerve is a cranial nerve, which means that it is part of the central nervous system, an extension of the brain. Each optic nerve contains about 1.2 million individual nerve cells, all of which travel with the optic nerve out the back wall of the eye, across the

orbit, and into the brain. The nerve then courses through the brain, connecting with other cells, which ultimately reach the back

of the brain, the occipital cortex, where our consciousness becomes aware of what we are looking at. As the optic nerve fibers travel through the brain, they can be damaged by tumors, aneurysms, blood clots, high fluid pressure around the brain, and the effects of injuries. When damaged by problems such as these or by loss of circulation, certain vitamin deficiencies, or toxins, the optic nerve often loses its normal rosy color and becomes pale.

The portion of the optic nerve where it penetrates the back wall of the eye is called the optic disk. The center of the optic disk may contain a depressed area called the optic cup. Some people have no discernible optic cup, whereas others have fairly large ones. The optic cup is important because it usually increases in size when the optic nerve becomes damaged by glaucoma. Its appearance therefore helps in the diagnosis of glaucoma.

The External Eye Muscles

Six straplike muscles control eye movements. Four muscles are called rectus muscles: the superior rectus, which turns the eye upward; the inferior rectus, which turns the eye downward; the medical rectus, which turns the eye inward; and the

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lateral rectus, which turns the eye outward. The word rectus means “straight” in Latin, and these muscles travel in a straight path. They are attached to the bones at the back of the orbit and travel straight to the eye, where they attach to the sclera. These muscles work in combination so

that the eye can move in any direction.

The other two muscles are the oblique muscles, which have somewhat complex actions. The superior oblique can turn the eye down-

ward and rotate it inward, while the inferior oblique can turn the eye upward and rotate it outward. The reason for the rotating motion of the eyes is that when you tilt your head to the left or the right, the eyes have to rotate in the opposite direction to compensate somewhat for the head tilt.

Of course, the brain coordinates the movements of the eyes so that both eyes are always moving in tandem. If they did not work this way, you would see double. In fact, this is exactly what happens when a nerve controlling a particular muscle or a group of muscles becomes paralyzed. The eye muscles can be affected by many problems, including inflammation (orbital myositis, thyroid disease), muscle diseases like myasthenia gravis, injuries, and inherited muscular disorders.

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C H A P T E R F O U R

Eye History and

Examination

WHEN YOU SEE YOUR EYE DOCTOR FOR A SPECIFIC PROBLEM, you describe the nature of the symptoms you are having.

This is called the history of your present illness. Then your eyes are examined and appropriate tests performed. Although today’s examinations employ sophisticated instruments and other gadgetry, the importance of the history should not be underestimated. In many cases, it may be more helpful in arriving at a diagnosis than the examination is. So when the doctor asks you what the problem is, don’t say, “You tell me, you’re the doctor!” Instead, describe your symptoms as well as possible. Be as succinct as you can: In today’s health care environment, unfortunately the time you get with the doctor may be rationed. As Sergeant Joe Friday used to say,“Just the facts, ma’am.”

Let us now go over the main components of the medical history.

The History

Chief Complaint

Just because you have a chief complaint doesn’t mean you’re a chronic complainer. The words chief complaint simply refer to the main reason for the appointment (for anything other than a routine examination). Examples may

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T H E E Y E C A R E S O U R C E B O O K

be “I have pain in my right eye” or “My vision became blurry after I had the headache.” The doctor often records your chief complaint in your own words.

Present Illness

Present illness refers to the nature of your symptoms. After mentioning your chief complaint, you can go into more detail about your symptoms. Have you had a loss of vision or some change in your vision? Have you had pain, irritation, discharge from the eye, or light sensitivity? Have you been seeing floating spots or flashing lights in your field of vision? If you have pain, what is it like? Is it a sharp or dull pain? Exactly where is it located? Is it present all the time or just occasionally? How severe is it? Do you have any other symptoms while you are having the pain? How long has each of your symptoms been present? If you forget to mention anything relevant, your doctor should ask you about it.

Medical History

Many eye problems may be related to diseases of the body. It is especially important to know whether you have any history of diabetes or abnormal blood sugars, high blood pressure, arthritis, infectious diseases, immune system problems, cancer, or colitis. Needless to say, any previous eye problems should be fully disclosed.

Current Medications

When you are asked what medications you are taking, give a complete list, not just prescription drugs but also vitamins, herbs, and any other supplements. Vitamins in large doses can sometimes act like drugs, and herbal supplements can interact with many prescription medications. You should give the name of each medication, the dose, how many times a day you take it, what you take it for, and any other relevant information. If you take a large number of medications, bring a list containing all of this information to your appointment. That way, the doctor or the assistant can either photocopy it or transcribe it into your record, and completeness is ensured.

Many prescription drugs can affect your eyes. For example, the cortisone type of medication can cause cataracts or increase the pressure in your eyes, a

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large number of medications can cause dryness of the eyes, and others sometimes have a direct toxic effect on certain structures of the eye.

Medication Allergies and Sensitivities

This is a very important category, because you don’t want to be prescribed products that contain medications to which you are allergic. Allergies to sulfa drugs, antibiotics, and adhesive on surgical tape should be mentioned. Anything that has caused hives or wheezing is especially important. You should also mention side effects you’ve suffered other than allergy, for example, stomach upset from penicillin or erythromycin, nausea and vomiting from codeine, and so on.

Family History

Many eye conditions are more common in some families than in others. Have any of your close relatives been diagnosed with glaucoma? Do people in your family tend to get cataracts when they are in their forties or fifties? Have any relatives had a retinal detachment? It is also important to know whether diabetes, high blood pressure, or allergies run in your family.

Social History

Many personal factors may have a bearing on your eye health. Do you smoke? Do you drink alcohol? If so, what kind and how much? What is your diet like? What are your current living arrangements like? Is anyone available who could help you instill eye medications, change your bandage, or help you get around after surgery?

The Eye Examination

Some procedures are used in virtually every eye examination, whereas some specialized procedures are used only on people who have certain problems. Of course, the completeness of the examination varies greatly from one ophthalmologist to another. Once you know what should be included in your examination, you can know how complete an examination you have had.

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Visual Acuity

Visual acuity is a measure of how well you can see. It is an important part of every examination of the eye. Visual acuity measures the clarity of your vision, that is, your ability to see details when you look straight ahead at something. It does not measure your peripheral (side) vision.Visual acuity is tested at a distance, usually twenty feet (or the equivalent in a room equipped with mirrors), and can also be tested up close at the reading distance, especially in people over the age of forty.

Distance visual acuity can be measured in a number of ways. Most commonly, an eye chart with letters of the alphabet is used. A disadvantage of this method is that some letters are easier to discern than other letters of the same size. There are also number charts that feature the numerals from zero to nine. For children who are not yet able to read letters, the E game is used. The letter E on the chart is oriented in any of four positions, and the child must point to show which way the “arms” on the E are pointing. To test near vision, we generally use reading material with print of different sizes.

Distance visual acuity is typically tested with each eye individually: The right eye is tested first with the left eye covered up, and then the process is reversed. If you are wearing glasses, we generally test with the glasses on. You hold a device called an occluder to cover the eye not being tested. It is important to keep your face pointed straight ahead during this test, because it is very easy to use the covered eye without knowing it. As you read the letters on the chart, do not squint but do try to read them even if they are not clear. You will usually be right more often than you would expect.

After reading the eye chart, with or without your glasses, you will often be asked to look at the same letters through a little device called a pinhole. You may be surprised to find that the letters look much clearer through the pinhole. Improvement in vision as you look through the pinhole usually means that you need a change in glasses prescription (or glasses if you do not have them now). The pinhole lets in only the rays of light that are least affected by one’s refractive error (nearsightedness, farsightedness, or astigmatism). Therefore, only the light rays providing the clearest image reach the eye. However, other eye problems, such as cataracts and scars on the cornea, can sometimes also allow improvement of vision with the pinhole.

The way you read the eye chart may provide other important clues. For example, if you consistently don’t see letters on the right side, this may indi-

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cate a problem with the right side of your peripheral vision. There may be a serious underlying problem, such as a blind area caused by a stroke, a tumor, or an aneurysm.

Distance visual acuity is recorded as a fraction, with 20/20 being considered the standard for normal vision. The first number in the fraction refers to the distance at which the visual acuity was

measured. If the first number is 20, then the person was standing twenty feet away from the eye chart. If a person’s visual acuity is 20/40, that means that the smallest letters that

person can see are twice the size of the letters that a person with 20/20 vision can see. Although 20/20 is considered the standard, most younger individuals with healthy eyes have better than 20/20 visual acuity either with or without glasses. For example, they may have a visual acuity of 20/15, 20/13, or even 20/10, which is about as good as it gets. If you have 20/10 visual acuity, you can see letters that are half the size of those on the 20/20 line.

If you do not have at least 20/200 visual acuity with your better eye while you are wearing the best possible glasses, then you are legally blind. Some people mistakenly say they are legally blind without their glasses, but of course they are not legally blind. Occasionally, one hears of an ophthalmologist who tells a patient that he or she is legally blind in one eye. Obviously, such an individual does not know the definition of legal blindness.

Near visual acuity, which tests vision at the reading distance, is generally tested on both eyes at the same time. Thus, no occluder is used. If you wear reading glasses or bifocals, you should wear them for this test, which determines the smallest size of print you can read. Near visual acuity may not be routinely tested in younger people but should be in people over the age of forty, especially people complaining of difficulty reading. If you complain of difficulty reading and your near visual acuity is not tested as part of your eye examination, head for the nearest exit! I have reviewed the records of people who sought an eye examination because of difficulty reading but who never had their reading vision checked during the examination. Instead, they were simply told they needed cataract surgery! Believe it or not, this is not a rare occurrence.

The way you read the near vision chart may shed some light on the nature of your problems. For example, if you read easily at first, but the letters then

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start to become blurry, or if you have to blink your eyes repeatedly to read clearly, you may have a type of dry eye problem.

Differences between one’s distance and near visual acuities may also provide information about underlying eye problems. Some types of cataract, for example, affect distance visual acuity more than near, whereas age-related macular degeneration may do the opposite. In some people who have both of these problems, it may be difficult to decide whether the reduction in vision is due primarily to the cataract or to the macular degeneration, and this is one way of determining which problem predominates.

Refraction

Refraction is the process by which your refractive error is determined. Your refractive error is essentially your glasses prescription for distance. If you have perfect vision at distance without glasses, then you have no refractive error. If a person with an eye problem has less than normal vision in each eye, the ophthalmologist often performs a refraction even if glasses are not going to be prescribed. The reason is that, in evaluating eye problems, it is often important to know just how well each eye is capable of seeing. The only way of accomplishing that is by performing a refraction.

Nearsightedness is the common term for the refractive error known as myopia. Nearsighted people can see things at close range, but beyond a certain point, everything appears blurry, and the farther into the distance they are looking, the blurrier things get. In a normal eye, the light rays entering the eye come to a focus on the retina in the back of the eye, just as a movie projector might focus an image on a screen. But in a myopic eye, the light rays come to a focus in front of the retina inside the eye.

Farsightedness is a misleading term commonly used for the refractive error called hyperopia.A hyperopic eye is out of focus at all distances, but the blurriness is worse at distance than at near. The problem is that the light rays coming from an object come to a focus behind the retina rather than right on the retina. Yet most hyperopic individuals see clearly when they are younger and only develop the blurriness as they become older. How can this be? Although the eye at rest is set to focus at distance, a focusing muscle (the ciliary muscle) in the eye acts like the zoom lens in a camera. When this muscle contracts, it changes the shape of the lens inside the eye and thereby changes the way the eye focuses. The eye

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uses this mechanism, called accommodation, to change its focus from far to near. As we become older, the ciliary muscle becomes weaker and weaker until it hardly works at all. This loss of ability to change focus with age is called presbyopia (described later). A young person, however, can use this focusing muscle to eliminate the blur caused by the hyperopia. By contracting this focusing muscle even when looking in the distance, that person can change the way the light rays focus in the eyes so that they focus on the retina and not behind it. But as the person becomes older and the focusing muscle weakens, the eyes lose the ability to compensate for the hyperopia, either partially or fully, and eyeglasses are then needed.

Sometimes older children or young adults, especially when under some tension, complain of blurry vision at distance and may appear to be myopic when a refraction is performed. However, they may be suffering from a spasm of accommodation. This occurs when the ciliary muscle has a certain degree of tightness or spasm. These individuals are accommodating, that is, using their near focusing mechanism even though they are looking into the distance. The diagnosis is suspected when they give variable answers as the refraction is performed. They seem to be focusing in and out, and they often remark as they look at the letters on the chart that they can sometimes see the letters for an instant but that the letters then blur up again. Spasm of accommodation can be confirmed by dilating the pupils with drops that temporarily paralyze the ciliary muscle (cycloplegic drops) and then performing another refraction. If spasm of accommodation is present, the apparent myopia should disappear. It is important not to overcorrect myopia or to prescribe glasses for people suffering from accommodative spasm, because that only strains the eyes. Reassurance and muscle relaxation exercises, as one might recommend for muscle tension headache, may be the best approach.

Astigmatism refers to another refractive error that may be present in either myopic or hyperopic individuals. Astigmatism is caused by the shape of the eye. Although the curvature of the front surface of the eye is almost perfectly rounded in a normal eye, the surface of the astigmatic eye curves more sharply in one direction than another. Thus, it is shaped more like a football than like a basketball. The result is that the light rays coming from all points on a given object you are viewing do not focus together on the retina, and this causes blurring. Fortunately, eyeglass lenses can correct the blurring.

Presbyopia, which you might call oldsightedness, refers to the gradual decline in ability to change the focus of the eye from distance to near. As mentioned

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