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

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Strokes

Here’s what happens in a stroke: Blood, which normally courses through an artery, suddenly can’t get where it needs to go. It’s blocked by a clog in the artery. Suddenly the tissue on the other side of the obstruc- tion—which needs the oxygen and nutrients in blood to stay alive—begins to die; it becomes ischemic, or oxygenstarved. If the clog opens in time, the tissue survives. If not, it dies.

We’ve already discussed strokes inside the eye (see “When the Eye’s Blood Supply Is Blocked” in chapter 15). These blockages of blood flow can also occur outside the eye, at sites along the visual pathways including the optic nerves, the chiasm (the meeting place at which the nerve fibers from each eye come together), and the cerebral cortex. Also, strokes can occur deeper in the brain; of these, the ones most commonly affecting eyesight occur in the parietal, temporal, and occipital lobes.

All strokes are not equal: the location of a blockage is crucial in determining the extent of the damage. A shutoff of blood supply to the retina or optic nerve—such as amaurosis fugax or ischemic optic neuropathy (see below), or a tumor along the optic nerve up to the chi- asm—usually results in partial or total loss of sight in one eye. Like two roads that intersect, optic nerve fibers meet at the chiasm before continuing on their journey toward the occipital lobe (see figure 1.8). An injury or stroke here at the chiasm or even deeper in the brain injures visual fibers of both eyes—and may result in partial

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loss of vision in both eyes, also called bilateral vision loss. A blockage or stroke in the parietal or temporal lobe can also result in partial loss of vision in both eyes. To make matters worse, the blow to eyesight usually isn’t the only damage. Most strokes here also cause specific neurologic problems, depending on the area of the brain that’s damaged. (In fact, the particular symptoms help

doctors pinpoint the exact location of the stroke.)

A parietal lobe stroke usually produces a similar pattern of visual field or peripheral vision loss in each eye, concentrated in the lower half of the field of vision. Also, the degree of loss usually varies; one eye may have more damage than the other. After a parietal lobe stroke, someone may also have difficulty with spatial orientation— becoming disoriented in a familiar place, for example, or having trouble reaching for a glass of water.

An occipital lobe stroke usually causes each eye to lose one-quarter or one-half of its field of vision, or to lose sight in the central visual field. Unlike parietal and temporal lobe strokes, this particular loss is often highly symmetrical—the damage in one eye is a carbon copy of that in the other. (This is because in the occipital lobe, both eyes’ nerve fibers exist almost side by side and may be equally affected by ischemia.) A temporal lobe stroke can cause partial vision loss, too. As with all strokes, the damage caused by those that affect eyesight may improve somewhat with time. Usually, however, at least some of the damage is permanent.

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Tumors

Tumors can also harm eyesight. These, like strokes, may occur anywhere, from the optic nerve in the front to the occipital cortex at the back of the brain. Here too the specific visual and neurologic problems can help pinpoint the area of damage.

Among the most common and significant of the tumors that affect eyesight are pituitary tumors. The pituitary gland is located below the optic chiasm, the place where the two sets of optic nerves come together. Think of the optic chiasm as a crossroads: The nerve fibers from one part of each eye’s retina (the temporal portion) pass straight through, on their way to the brain’s occipital lobe. The fibers from another part of the retina, the nasal portion (the fibers that transmit images from our peripheral vision), cross here.

If a pituitary tumor grows large enough to press on the chiasm, it can disrupt these crossed fibers and cause someone to lose side vision. If your doctor suspects that you might have a pituitary tumor, you’ll probably need visual field testing (see chapter 3) and a brain-imaging test such as an MRI scan. The good news here is that there are several good treatments for pituitary tumors, including medication and surgery. Bromocriptine is a medication that is very effective for treating prolactin-se- creting pituitary tumors. Many people are able to return to normal activity—including driving and playing sports —and many have a near-complete restoration of their vision.

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Collagen Vascular Diseases (Arthritis and

Its Relatives)

The broad term collagen vascular diseases encompasses many disorders, all linked because they cause inflammation and scarring of connective tissue (the cells and fibers that make up the body’s framework and system of sup- port—things like cartilage, bone, and elastic tissue). In many of these disorders the body appears to attack itself. This autoimmune reaction usually occurs throughout the body, and it frequently involves the eye—which is why regular eye examinations and prompt attention to any eye problems are essential. Here are some of the most common of these diseases and their consequences in the eye (these symptoms are covered separately elsewhere in this book):

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Thyroid Disease

The thyroid gland sits in the neck, over the trachea, just below the larynx, or “Adam’s apple.” It has two halves, one on each side of the trachea, connected by a thin isthmus of tissue. (Most people can’t feel their thyroid. But as a diseased thyroid gets bigger, it can become easier to feel, especially when you swallow. A massively enlarged thyroid, also known as a goiter, is hard to miss.)

The thyroid gland secretes thyroid hormone, which is crucial for metabolism and body regulation. Its intricate effects on the body are too numerous to describe here, but the thyroid keeps us at an even keel. Basically, producing too much thyroid hormone (a condition called hyperthyroidism) makes someone anxious and overactive; producing too little (hypothyroidism) makes someone tired and lethargic.

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How does the eye become involved? Well, in thyroid disease, as in collagen vascular diseases, the body turns on itself; it creates antibodies (cells designed to fight off infection and disease) that act against normal tissue. In thyroid disease, the body’s confused immune system attempts to protect or immunize itself against normal thyroid tissue. The consequences of this “mistaken identity” can be serious, for as the body fights its own thyroid gland, it also attacks other tissues—perhaps mistaking them for thyroid tissue as well. Some of these chemical weapons specifically target the eye. This leads to an inflammatory reaction in the connective tissue of the eye’s muscles, fat, and soft tissues. The result: fibrous scarring and fluid swelling.

There are many medical names for what’s happening in the eye, including Graves’ ophthalmopathy, or Graves’ disease (after one of the early investigators of this condition), infiltrative ophthalmopathy, endocrine ophthalmopathy, and thyroid eye disease. There are also many symptoms, including bulging eyes (called proptosis); edema, or swelling, of the eyelids; retraction of the eyelids; swelling of the conjunctiva; drying and ulceration of the cornea; problems with double vision; and optic nerve damage.

Most people with thyroid eye disease—about 80 per- cent—are hyperthyroid. (Up to 40 percent of people with hyperthyroidism eventually develop some degree of eye trouble.) The disease affects more women than men, and it usually strikes people in their thirties and forties.

Thyroid eye disease is very unpredictable in its onset,

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progression, severity, and duration. Often it moves slowly, with remissions and advances lasting from months to years. But sometimes it’s fast and relentless. One of the most frustrating aspects of thyroid eye dis- ease—and the most difficult feature for doctors as well as patients to understand—is that regulating the thyroid gland itself often has little or no effect on the course of the eye disease. In fact, the eyes can become affected even decades after the thyroid disease has been under control. Thus, if you have thyroid disease, regular eye examinations are crucial!

One means of organizing and cataloging the thyroid’s degree of ocular involvement is called the NOSPECS classification:

Class 0: No physical signs or symptoms of thyroid eye disease

Class 1: Only signs (but no noticeable symptoms) Class 2: Soft-tissue involvement

Class 3: Proptosis (bulging eyes)

Class 4: Extraocular muscle involvement Class 5: Corneal involvement

Class 6: Sight loss (due to optic nerve involvement)

In Class 1 disease, patients don’t have any noticeable symptoms, but eye doctors can detect early signs of thyroid eye disease. One such sign is a tightening of the upper eyelid so that it can’t close all the way, all the time, producing problems with dryness. Another is “lid lag,” in which the eyelid can’t close quickly, as in a blink, but seems to shut in slow motion.

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In Class 2, the soft tissue begins to swell, or have edema. The eyes may look puffy and may appear to have bags below them. The conjunctiva may appear watery, swollen, or thickened.

In Class 3, proptosis, or bulging eyes, becomes a problem. (This is largely due to the concentration of the thyroid antibody in the extraocular muscle and the inflammation this causes.) As these muscles enlarge, they push the eye out from behind, making it shift forward so that it appears to be bulging out of the socket. This can happen in both eyes, or in one.

In Class 4, as the extraocular muscles become increasingly swollen and inflamed, it becomes harder to move them; it’s particularly difficult to look up. Double vision also becomes common as the eyes lose their ability to move together. (Ultrasound, a painless imaging technique, may be helpful in determining the extent of this problem.)

In Class 5, severe dryness is common, because the eyelids are no longer able to cover the bulging eye. This causes exposure keratitis, which can range from mild dry spots on the cornea to ulcers on an extremely parched cornea. Compounding the dryness problem, the eye’s ability to make tears is hampered as inflammation and scarring encompass the lacrimal, or tear-making, glands. Treatment at this stage involves the use of lubricants for the dryness, and sometimes surgery to help the eyelids close.

In Class 6—a degree of ocular involvement experienced by fewer than 5 percent of patients with thyroid

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eye disease—the optic nerve may be damaged by the prolonged inflammation and swelling, and sight may be damaged or lost. (The optic nerve can be damaged even if the eyes aren’t noticeably bulging—another reason why regular eye examinations are essential.)

Treatment: The first task is to get the thyroid under control. However, if you have any kind of thyroid irregularity, your eyes may still be at risk; thyroid eye disease can occur even in people with normal or low levels of thyroid hormone. Thyroid eye disease can occur in people with normal thyroid function; in this case it is called euthyroid Graves’.

In the early stages of thyroid eye disease, lubrication with tear-substitute drops and ointments, along with increased humidity (see chapter 13), can be very helpful in easing symptoms. More lubrication may be needed if the eyes begin to bulge. Taping the eyelids shut at night may help keep the eyes from drying out during sleep; in some cases, special goggles can help keep the eyes moist. If the eyelid’s ability to close is poor, then tarsorrhaphy, a surgical technique that partially closes the eye, may also help. In advanced cases, oral steroids, radiation, and surgery for decompression and lid positioning may help.

Acne Rosacea

Acne rosacea—a skin condition different from the acne most of us suffered as teenagers—mainly targets the forehead, nose, cheeks, and chin. But the eyelids have skin too, and they’re not immune from this annoying

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problem. (Eyelid acne is often seen in people with facial acne.) The symptoms here can range from mildly irritating to disabling. Many people with this condition develop a chronic blepharitis with a mild conjunctivitis (see the discussion of conjunctivitis in chapter 12); but if the problem isn’t treated, it can lead to corneal scarring and new blood vessel growth, which may eventually impair vision.

Rosacea of the eyelids is very difficult to treat, and treatment usually takes months. An oral antibiotic, such as tetracycline, is often prescribed, along with lid “shampoos,” warm compresses, and an antibiotic eye drop or ointment. (See the discussion of blepharitis in chapter 10.) Even after the condition is under control, you may need to continue this daily regimen for years.

Parkinson’s Disease

Parkinson’s disease is characterized by progressive, involuntary tremors, caused by a loss of chemical-produc- ing nerve cells in the brain. People with this disease develop a “wooden” face, with decreased blinking, little eye movement, and the appearance of a fixed stare. Because blinking is one of the eye’s ways of maintaining moisture, a perpetual lack of blinking causes dryness. Tear substitutes (drops and ointments), along with increased humidity, can be very helpful here. Another problem, stemming from the decrease in head and eye movement, is difficulty in using bifocals. Many people with Parkinson’s disease find it helpful to keep two pairs of eye-