Ординатура / Офтальмология / Английские материалы / The Eye Care Sourcebook_Lavine_2001

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where the endothelium is located may reveal the presence of guttata, tiny dots, in that area. People with Fuchs’s dystrophy have such dense guttata formations that the back surface of the cornea has a beaten metal appearance. Thin, vertical wrinkles may also be visible in the endothelial layer. By shining the light of the slit lamp in at the correct angle and by using high magnification, the ophthalmologist can actually see the endothelial layer directly. It looks something like the tile floor in an old bathroom. If many endothelial cells have been lost, the remaining cells become enlarged and sometimes irregular in shape as they fill in the remaining space. A special instrument can also be used to actually estimate the number of endothelial cells in a given area. An indirect measure of how well the endothelial cells are doing their job is to measure the thickness of the cornea. It becomes thickened even before any edema becomes obvious, and this means that the endothelial cell function is compromised. Edema itself may be very subtle or quite obvious to the doctor, depending on its severity.

Treating Corneal Edema

If the edema is very mild, its effect on vision may be minimal. Any blurring or halos around lights may be most noticeable soon after you awaken in the morning. This occurs because less oxygen gets to the eyes while they are closed during sleep. One treatment you can try is to hold a hair dryer at arm’s length and direct air of moderate warmth toward the eyes. The heat causes a little of the water in the cornea to evaporate, thereby bringing about improvement in vision.

Another helpful technique is using over-the-counter eyedrops and ointment that contain hypertonic saline. Saline is nothing more than salt water that, in this case, comes in a 5 percent strength. Hypertonic saline may sting a little because of the high salt content, but it works by drawing water out of the cornea. The ointment, which can blur vision, is generally used only at bedtime. The drops can be instilled every few hours. Very frequent use, say, more often than every two hours, should be avoided because the chemical preservatives in the drops can be mildly toxic to the cornea. If the drops sting too much, a 2 percent strength is also available.

If the surface of the cornea has developed tiny blisters from the edema and is painful, a special soft contact lens called a bandage lens can be placed on the eye, where it remains continuously. Sometimes such a lens can even draw a little fluid out of the cornea. Unfortunately, in some cases it can make the edema

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worse, and there is always the risk of developing an infection in the cornea with such a lens in place.

Ultimately, if the blurring from the corneal edema is becoming disabling, a corneal transplant, a major operation, can be performed. The central part of the cornea, measuring less than a third of an inch across, is taken from the eye of someone who has donated his corneas and is sewn in place after the central cornea from the person receiving the transplant is removed. The operation has a high success rate, on the order of 90 percent,

but rejection or edema of the transplanted cornea, infections, and other complications can occur. A cataract operation with lens implant can be performed at the same time

in someone who also needs cataract surgery. For people who have previously had cataract surgery, the lens implant can remain in place, or it can be replaced with a different lens implant if the physician feels that the original implant was contributing to the decompensation (clouding) of the cornea. After a corneal transplant, the stitches must be left in for a long time, a year or even more. It usually takes at least a year for the eye to heal and for the vision to stabilize with this type of surgery. Sometimes, mild distortion of the cornea, depending on how it heals, may affect the final vision by causing astigmatism, but the blur caused by astigmatism can often be corrected by eyeglasses.

Other Corneal Problems That Cause Clouding

Many inherited conditions called dystrophies can affect the cornea. Fortunately, most of these are quite rare. A common but usually very mild condition is called map-dot-fingerprint dystrophy. It usually occurs in people of northern European descent. Its name is derived from

its appearance when the cornea is examined through the slit lamp. Near the center of the cornea, just deep to the surface layer of cells, one may see several fine, wavy lines reminis-

cent of a fingerprint. In other people, there may be an irregular area that looks like the outline of a country on a map. Sometimes, tiny, whitish dots may be seen as well. Map-dot-fingerprint dystrophy may affect vision in the most severe cases, but for most people, it is just a comfort problem. The irregularity

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near the surface of the cornea sometimes causes a slight breakdown in the cornea’s epithelium, and this may feel like a small scratch on the eye.

Other irritative eye problems, such as blepharitis and dry eye syndrome, may, if present, be contributing to the surface irregularity. Treating these other conditions may take care of the symptoms. A mild hypertonic saline eyedrop, as described earlier, may also help flare-ups to resolve more quickly. If you are told you have this type of dystrophy, it should not be a major cause for concern. Most people who have it are not even aware of it, and it is simply brought to their attention by a conscientious ophthalmologist who has taken the time to do a very careful examination.

Several dystrophies that affect the thick, middle layer of the cornea, the stroma, include granular, lattice, and macular dystrophies. These produce cloudy patches in the cornea that can affect vision. The macular form is the most severe of these, followed by lattice. In people in whom vision is severely affected, a corneal transplant operation may be necessary.

Keratoconus is a bulging, stretching, and thinning of the cornea. It occurs in teenagers and young adults and has a genetic basis. Affected individuals may have a history of seasonal allergies or may

have close relatives with such a history.

The irregularity in the cornea produced by keratoconus causes a focusing error called irregular astigmatism. Irregular astigmatism,

unlike regular astigmatism, cannot be fully corrected by eyeglasses. Therefore, people with keratoconus need to be fitted with rigid contact lenses if they desire to see more clearly. The fitting process can be difficult in more advanced cases, and special types of contact lenses are sometimes required. When contact lenses are no longer effective, corneal transplantation, with a success rate of well over 90 percent, can be done.

Corneal Infections and Ulcers

Infections of the cornea are quite serious because they threaten the entire eye. They may be caused by bacteria, viruses, fungi, and other organisms. The herpes viruses usually produce superficial infections, although they can still cause scarring and loss of vision. (See chapter 13.) Fungus infections are among the most dreaded but fortunately are fairly rare. Infections caused by

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bacteria have become more common in the past thirty years because of contact lens wear.

The cornea’s epithelium is the first barrier against infection, just like the skin. Usually a break must occur in this layer for infection to occur. Another defense against eye infection is the antibodies in the tears. That’s why people who have dry eye syndrome are at higher risk for infection.

A corneal abrasion can allow bacteria to enter and begin multiplying. A foreign body that lodges in the cornea also breaks the surface and can allow bacteria to enter.

People who wear contact lenses often suffer tiny abrasions that they may not even notice. The abrasions occur as the lenses are being inserted and removed. Soft contact lenses, which contain

water, may be contaminated by bacteria. Their use entails a higher risk of infection than does rigid contact lens wear. That is why proper disinfection techniques and han-

dling of contact lens solutions are so important. Wearing soft contact lenses on an extended wear basis, that is, not removing them at night, increases the risk. Being a smoker also increases the risk—possibly related to tars on the fingers (or on the lenses themselves) that encourage bacteria to stick to them.

How Ulcers Form

Once the bacteria start to grow in the cornea, a small, superficial cloudy spot called an infiltrate appears at the site of entry. This spot is caused by edema and the migration of white blood cells, part of the immune system, into the area. Soon the surface layer of cells sloughs off in the area over the infiltrate.

The infection then continues to eat away at the cornea, causing an ulcer. Corneal ulcers can become quite deep and, if left untreated, cause a perforation of the cornea.

If this happens, fluid from inside the eye leaks out, the bacteria gain entrance to the interior of the eye, and the eye may be lost. Thus, prompt recognition of the infection, identification of the cause of the infection, and treatment are essential.

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Determining the Cause of Infection

If an ulcer is already present,it must be cultured.An anesthetic eyedrop is instilled in the eye to numb it, and a thin platinum spatula that has been sterilized with a flame is used to scrape the surface of the ulcer. The scrapings are then smeared directly onto culture plates if available and sent to the laboratory. Otherwise, the scrapings can be sent to the laboratory in a special tube and then smeared onto the culture plates. The laboratory incubates the plates, storing them at a set temperature and watching closely for the growth of bacterial colonies. If any appear, the type of bacterium (or fungus) is identified, and special tests are performed to determine the antibiotics to which it is most sensitive. However,it can take twentyfour to forty-eight hours or more to obtain culture results, and we don’t want to wait that long to begin antibiotic treatment. Therefore, a little of the scrapings is smeared directly on a glass slide, treated with special stains, and viewed right away under the microscope. This can often give a clue as to which bacterium is causing the infection, and an appropriate antibiotic can then be selected.

Treating Corneal Ulcers

Systemic antibiotics—those taken by mouth or injected—are generally not helpful in treating corneal ulcers. Treatment consists of very frequent instillation of antibiotic eyedrops. In some cases, we may fortify standard eyedrops by adding very concentrated solutions of the antibiotic to them. This extra strength is sometimes needed to combat the infection. In addition, antibiotic solutions are sometimes given by injection, once or twice a day, under the conjunctiva, the clear membrane over the white of the eye. This sounds painful, and sometimes it can be. But these shots are only given until it is clear that the infection is being brought under control. The eye is examined once or twice a day, and if it appears that the ulcer crater is healing in, then we know that things are moving in the right direction and that the choice of antibiotic was correct. If things are not going well, then another antibiotic can be tried. The choice of antibiotic is then guided by the results of the culture.

Preventing Corneal Ulcers

The best approach to the problem of corneal ulcers is prevention. If you feel that you’ve scratched your eye, have it checked right away so that prophylactic sulfa or antibiotic treatment can be given. If you see a white spot on your

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cornea, have it checked out right away. If you wear contact lenses, disinfect them exactly as you are supposed to. Keep the case clean. Discard old or possibly contaminated solutions. Wash your hands thoroughly before inserting or removing the contacts. Enjoy your contacts, but remember that there is a risk to using them.

Conjunctivitis

Conjunctivitis is an inflammation of the conjunctiva, the nearly clear membrane that covers the white of the eye as well as the inside surface of the eyelids. The inflammation causes the blood vessels in the conjunctiva to dilate, giving the familiar appearance of bloodshot eyes.

Causes of Conjunctivitis

When we think of conjunctivitis, we usually think of infection, but allergies (see “Allergies and the Eye,” page 98) and various irritants can also cause inflammation. For example, injuries, foreign bodies, chemicals such as acids, and contact lens problems are other possible causes. But if your eyes become red and irritated and there’s no obvious reason, it’s a good bet that you’ve contracted an infection.

If we feel that an infection is present, we must first determine the type of infection. The term pinkeye that you may sometimes hear does not have a precise meaning, because any infection will cause a pink eye. Viruses, bacteria, and fungi can all infect the eye. The treatment depends on the type of infection, so we must first look for the clues that point us in the right direction.

Determining Whether an Infection Is Viral or Bacterial

Viral infections (viral conjunctivitis) are by far the most common type. They are often caused by the viruses that cause colds. The cold symptoms may occur before, during, or after the eye infection. Therefore, if someone with infected eyes has a sore throat or has had a sore throat in the preceding week or so, it’s likely that viral conjunctivitis is present. It’s also common to hear that one or more people in the person’s family or other immediate environment has had conjunctivitis or a cold recently.

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Viral conjunctivitis usually involves both eyes, but it may take several days before the second eye is involved. The second eye usually has milder symptoms than the first. The most common symptoms are burning, irritation, scratchiness, tearing, mild itching, light sensitivity, and a feeling of something in the eye. The eyelids may be crusted somewhat or even stuck shut when you awake in the morning, but the discharge during the day is watery, not puslike. With bacterial infections, in contrast, we often see a thick discharge during the day, although in some cases the discharge may be scanty.

When we examine the eyes, we look for a number of features that are characteristic of viral conjunctivitis. The eyes tend to have a glassy look because of the excess of tears. We feel for a little knot of

tissue called a lymph node (gland) just in front of the ear and below the arch of the upper jawbone. These lymph nodes, which

are part of the immune system and help fight infection, usually enlarge with viral infections but not with bacterial infections.

Sometimes we can actually feel the enlarged node; other times we may not actually feel it but may find that the area where the node should be is somewhat tender when we press on it. Next, we pull down the lower eyelid (something you can do also) and compare the degree of redness of the conjunctiva on the inside surface of the lid with that on the white of the eye. In viral conjunctivitis, the conjunctiva on the inside of the lid is often much redder. Not only that, but the conjunctiva lining the inside of the lid will have a granular appearance, as compared with the smooth, glassy appearance it normally has. When we examine it through the slit lamp, which magnifies its appearance, we see that the granular appearance is caused by the cropping up of numerous tiny, translucent bumps called follicles. These follicles contain lymphoid tissue, just as the lymph nodes do. Bacterial conjunctivitis usually does not cause significant lymph node enlargement or formation of follicles.

We also use the slit lamp to look more closely at the conjunctiva over the white of the eye. With some forms of viral conjunctivitis, we may see not only the dilated blood vessels but also small hemorrhages where a little blood has actually leaked out. Examination of the cornea of the eye is also important. Usually, no abnormalities are seen until we instill a little dye called fluorescein in the eye. It’s called fluorescein because it fluoresces and shows up as a bright green when a special blue light is shone on the eye. This dye is taken up by the cornea

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wherever the surface cells of the cornea have sloughed off. With viral infections, we sometimes see numerous pinpoint dots of fluorescein all across the cornea.

By combining the history (symptoms related by the patient) with what we find when we examine the eye, we can usually tell that a viral infection, as opposed to a bacterial infection, is present. That’s important, because

the treatment for the two types of infection is different. Of course, there will always be some infections that appear to be in a gray area and for which the cause is not obvious.

Treating Viral Conjunctivitis

For most viral infections, there is no specific treatment to eradicate the virus. The infection just has to run its course, and that is generally anywhere from four days to two weeks. Viral infections are usually highly contagious. They are generally spread by hand-to-hand contact. People with the infection rub their eye (or nose or mouth) and either touch someone else or touch something that someone else touches. So when we examine someone with such an infection, we make sure to clean off everything that person has touched, including the doorknob on the way in! We also advise the patient not to touch anyone else and not to share the same washcloth with anyone else. Treatment is symptomatic: Over-the-counter eyedrops such as artificial tear drops or decongestant eyedrops (the ones that reduce the redness) can be helpful. Holding a cool, moist washcloth over the closed eyelids can also be helpful.

The eyelids and eyelashes should also be kept as clean as possible. Antibiotics are ineffective against viral infections

Why not treat with antibiotic or sulfa eyedrops? Very simple—these drops only fight off infections caused by bacteria, not those caused by viruses. Using such drops when they are not needed is not only a waste of time and money but can also be harmful in a number of ways. First, people can develop allergies to antibiotics when they use them in their eyes. That prevents them from being able to use the same antibiotic in the future. There may also be toxic reactions to some antibiotics. Second, if an infected eye stays red, it may be hard to determine whether it is still red because the infection is not going away or because an allergic reaction to the drops is occurring. Third, we should

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remember that just as we don’t like to use antibiotics by mouth unnecessarily for fear of destroying the “good” bacteria that live in our intestines, we also don’t want to get rid of the “good” bacteria that live in the conjunctiva of our eyes. Getting rid of such good bacteria can allow bad bacteria to multiply, and we may then have a much more serious infection to deal with. Fourth, use of antibiotics when they are not needed helps bacteria develop resistance to antibiotics, which then become useless when we really need them. That’s why you should never ask your doctor to prescribe an antibiotic for you if you don’t really need it. Finally, use of antibiotic drops can lead to a false sense of security that the infection is being treated. The infected person may then touch other people and continue to spread the infection.

A common dilemma occurs when children in school who develop viral conjunctivitis are sent home and told they can only return once they have begun treatment with antibiotic eyedrops. Unfortunately, such drops usually end up being prescribed. This should not be

done for all of the reasons just mentioned. Teachers, school nurses, and others (including some doctors) need to be educated about the appropriate treatment of viral infections.

Eyedrops that contain corticosteroids (cortisone) should not be used to treat viral conjunctivitis. They impair the immune system and allow the virus to remain alive and active for a longer period of time.

Furthermore, a herpes simplex type of viral conjunctivitis may be indistinguishable from the usual types of viral infections, and using a cortico- steroid-containing eyedrop in the presence of herpes simplex definitely worsens the prognosis. In the specific situations in which corticosteroid eyedrops are indicated, they should be prescribed only by an ophthalmologist, although they are abused by many ophthalmologists as well.

What If the Conjunctivitis Does Not Get Better?

If the conjunctivitis does not get better in the expected two weeks, we may suspect another type of infection. For example, there are eye infections caused by a primitive type of bacterium called chlamydia. It may look very similar to a viral conjunctivitis, but rather than resolve on its own, it continues on as a chronic infection. The conjunctiva lining the inside of the eyelid can be

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swabbed and a special test performed to confirm the diagnosis. Chlamydia is usually transmitted as a venereal disease, and it may also be seen in newborns to whom it is transmitted as they pass through the birth canal. Chlamydial infection is usually treated with antibiotics by mouth. This clears up not only the eye infection but also any chlamydial infections elsewhere in the body.

If someone with conjunctivitis has been using an eyedrop for symptomatic relief, it is also possible that an allergy to some component of the drop has developed. If we suspect that this is occurring, we discontinue use of the eyedrop and see whether the eye then improves.

Treating Bacterial Conjunctivitis

Many cases of bacterial conjunctivitis resolve on their own without treatment. The body’s immune system takes over and eradicates the infection. Nevertheless, we usually treat these infections to make them go away more quickly. However, infections caused by the staphylococcus (or staph) bacterium may not resolve on their own. This type of infection is often associated with chronic blepharitis, a low-grade chronic inflammation of the oil glands in the eyelids.

The oil glands tend to harbor the staph bacteria. If a staph infection of the eye is not treated, it may become chronic, and then it is much more difficult to eradicate in the future. Another exception

would be certain very virulent bacteria, such as the one that causes gonorrhea. Bacterial infections such as these require intensive treatment.

If the bacterial conjunctivitis is related to chronic blepharitis, we often see very little discharge. Treatment of the underlying blepharitis is the key here. (See “Blepharitis,” page 59, in chapter 6.) The conjunctivitis component is generally treated as well with either sulfa or antibiotic eyedrops.

Sulfa eyedrops are often effective because they are available in high strengths for use in the eyes. However, they have some disadvantages. First, sulfa drugs are inactivated by a chemical (para-aminobenzoic acid) found in puslike discharge, so they may not be a good choice if much discharge is present. Second, some people are allergic to sulfa drugs. Finally, these drops tend to sting a bit.

Many antibiotic eyedrops are available, and they are all fairly effective. Cost factors as well as the chance of toxic or allergic side effects help dictate the choice. If the discharge is smeared on a glass slide for analysis under the microscope

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