Ординатура / Офтальмология / Английские материалы / The Eye Care Sourcebook_Lavine_2001

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the condition of the retina is usually the limiting factor that determines how well the eye sees after cataract surgery. In some cases, this may mean that no improvement in vision occurs after cataract

surgery, and any surgery performed in such a situation will have been in vain.

To determine whether improvement in vision is likely after cataract surgery, the

physician must carefully evaluate the cataractous lens to determine whether the cloudiness is sufficient to cause the patient’s complaints. One way to do this is to look into the eye through an undilated pupil with an ophthalmoscope, the instrument used for examining the retina. If what a person sees through an eye seems blurred, then what the physician sees looking into the eye should be blurred as well. The macula must also be carefully checked for changes in its appearance that would signify the presence of macular degeneration.

In short, cataract surgery is indicated if a person, even with the best possible glasses, is unable to see well enough to perform everyday activities, and only if the cataract is severe enough to explain the poor vision, with no other disorder in the eye that would prevent improvement of vision. Clearly, if these criteria were followed, the number of cataract surgeries performed would be a fraction of what they are today.

My recommendation is that when your doctor discusses the possibility of cataract surgery, get a second opinion. From whom? From yourself! Because only you can decide when you should have

the surgery. Remember, any surgery can have complications. If you are functioning well with the vision you have and the cataract

symptoms are only a mild annoyance or minor inconvenience, surgery is inadvisable. However, if the vision problems are interfering significantly with your work, driving, reading, or ability to function in general, then you should consider the surgery. Except in rare situations (such as mature or totally opaque cataracts), there is no medical necessity or urgency for the surgery.

Alternatives to Surgery

No medication can reverse the cloudiness caused by cataract. However, with the posterior subcapsular type of cataract, which often begins with a small, cloudy spot located centrally, a mild dilating type of eyedrop can often produce

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a nice improvement in vision. Enlarging the pupil in this way often allows the light rays entering the eye to bypass the central cloudy spot. Of course, this is only a temporary solution that will no longer work when the cataract becomes more advanced. It may also be less practical for people who live in very sunny climates. But it is useful when the patient would like to “buy some time” before undergoing surgery.

Glare problems caused by cataract can sometimes be mitigated by wearing sunglasses, or at least tinted glasses that block out the blue wavelengths of light. Some people object to the yellowish tint that these glasses

impart. And since cataract often reduces the amount of light entering the eye, tinted glasses may aggravate the vision problem under some circumstances, e.g., at night.

Finally, remember that if the vision problem is mainly at the reading distance, the reading glasses or the reading portion of the bifocals can often be strengthened. This will make you hold your reading material closer to your face, but many people do not mind doing that if it allows them to avoid surgery.

How Cataract Surgery Is Done

Cataract surgery means removal of the lens. It is a surgical technique and is not performed using a laser, although that is a common misconception. Don’t make the mistake of choosing a surgeon on the basis of the method of cataract removal. All current methods of removal are highly effective. All that matters are the conscientiousness, skill, and dedication of the ophthalmologist in whose care you have entrusted yourself. Does it really matter whether one stitch, two, or none at all is used? What mat-

ters are that the surgery is well done and there is no leakage from the incision afterward. Does it matter how the surgeon numbs the

eye? Avoid individuals who advertise that they perform this or that technique with the implication that it is superior to the techniques used by other surgeons. These are just marketing gimmicks employed to lure in the gullible.

Cataract surgery is usually performed by what we call an extracapsular technique. This means that rather than removing the entire lens intact in one piece, as was usually done prior to 1980, the surgeon removes the lens piecemeal. A

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small incision is made in the eye, and an opening is then created in the anterior capsule, the front part of the envelope that surrounds the lens. The nucleus, or central portion of the lens, can then be removed in one piece, or, more commonly today, a technique called phacoemulsification is used to pulverize the lens using an instrument that employs ultrasound (high-frequency inaudible sound waves). The nucleus remains in its normal position in this eye as it is pulverized, and the fragments are removed from the eye by a suction-producing vacuumlike instrument. After removal of the nucleus, the remaining cortex of the lens is then removed with suction, with care being taken not to cause any rents in the portion of the lens capsule that remains. This back portion of the lens capsule is left intact because it is safer for the eye, especially the retina, that way.

Remember that the function of the lens is to focus incoming light rays onto the retina. Removal of the lens makes the eye extremely hyperopic (farsighted). A lens in eyeglasses that would correct this hyperopia is quite thick, has a magnifying effect (about 25 percent), and tends to distort things in your peripheral vision. Because of the magnification, it cannot be used together with an eye that has not undergone cataract surgery. Although glasses can be used to correct vision in people who have had cataractous lenses removed from both eyes, many people do not like the quality of vision they obtain with “cataract glasses.”

Contact lenses after cataract surgery only magnify what you see about 10 percent, and there is no distorting effect. However, many older people cannot or do not want to deal with contact lenses.

Therefore, the lens implant was developed. An intraocular lens implant, which is an artificial lens with flexible loops that wedge the lens in place, is inserted at the time of

cataract surgery into the remaining portion of the lens capsule inside the eye, where it can focus incoming light rays just as the eye’s natural lens did. Prior to the surgery, special measurements of the eye are done to estimate what power of lens to insert in the eye. But it is only an estimate, and glasses may be needed afterward to “fine-tune” the vision. Generally, these are bifocals.

Significance of the Incision Size

In the long run, the incision size does not matter much. In the short run, a shorter incision allows the eye to achieve stable, clear vision much more

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quickly than a larger incision does. However, the end result is usually excellent in either case. One reason for using a larger incision would be an eye with a small pupil that dilates poorly. A larger inci-

sion would allow more room in which to operate and may be safer for the eye.

Cataract surgery with both large and small incisions has been associated with long-term

lowering of the intraocular pressure, a definite boon to people who have glaucoma or might develop it in the future. However, in my hands, extracapsular cataract surgery with the larger incision has resulted in a greater lowering of the pressure than is generally seen in patients who have undergone phacoemulsification with the smaller incision.

Complications of Cataract Surgery

Cataract surgery is one of the most successful types of surgery, and at least 95 percent of the time, improvement in vision is achieved. But, as with any surgery, there can be complications, even total loss of vision or of the eye. Occasionally, additional operations are required. That is why you should not have the surgery unless you really need it.

One major complication is infection inside the eye, which occurs in 1 out of every 500 operations and results in loss of the eye about half the time. About 1 percent of the time, clouding of the

cornea occurs, a complication that requires another major operation, a corneal transplant. Retinal detachment, also with a 1 percent incidence, requires surgery that is successful 90 percent of the time. It can occur right away or

many years after a cataract operation. Bleeding in the eye, continued inflammation, glaucoma, double vision, dislocation of lens implants, and cystoid macular edema (fluid buildup in the center of the retina that blurs and distorts the vision) are other possible complications.

Recall that the surgery is performed in such a way as to leave the back portion of the capsule that surrounds the lens intact. However, should a tear in this part of the capsule occur during the operation, the vitreous (gel-like substance) that fills the inside of the back part of the eye may come forward. This

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problem, called vitreous loss, greatly increases the risk of many of the complications just mentioned. To minimize the risk, this extruded vitreous must be removed very carefully from the front of the eye, and if insufficient support from the remaining lens capsule is left, sometimes a different style of lens implant must be inserted. An even more chal-

lenging problem arises if parts of the central core of the lens, the nucleus, fall back through the tear in the capsule. They must then be carefully recovered using special techniques.

Although not a true complication, clouding of the posterior capsule, the portion of the lens capsule that remains in place behind the lens implant, occurs in up to 50 percent of people within a few years of the cataract surgery. This is called secondary cataract, and it causes blurring very similar to that caused by the original cataract. The blurring can be eliminated by creating a hole in the center of the cloudy capsule with a special laser called a neodymium: YAG laser. Such a treatment will slightly increase the risk of developing a retinal detachment or macular edema, two of the complications mentioned earlier.

This discussion of possible complications is not meant to scare you. It is simply to let you know that any surgery, from the most minor on up, can have complications.

Summary and Recommendations

When chemical changes occur in the proteins of the eye’s crystalline lens, the lens loses its clarity, a condition we call cataract. These changes appear to be triggered by a series of oxidation reactions. The lens and the fluid surrounding it maintain high levels of antioxidants, which can help keep the lens healthy. Over time, however, the oxidative stresses in the lens’s environment can overcome the eye’s defense mechanisms. Preventing cataract may be a matter of keeping the antioxidant systems finely tuned and in top working condition. Since antioxidants are derived from the diet, a nutritional approach seems the most natural and may prove effective.

Lutein, a yellow antioxidant pigment in many dark, leafy green vegetables, may help prevent cataract. Consuming at least one serving a day of these

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vegetables is recommended. Vitamins C and E and other antioxidants in vegetables and fruits are felt to play an important role as well. People who consume more vegetables and fruits are at lower risk for cataract and other degenerative problems. Consuming at least eight servings a day is recommended. For people over age sixty-five, a daily multivitamin/multimineral supplement may also be helpful.

Cataract surgery is highly successful but should be considered only when you feel it is necessary to improve your vision. Even with perfectly performed surgery, the eye is never quite the same as it was before the cataract developed.

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Glaucoma

GLAUCOMA IS A DETERIORATION OF THE OPTIC NERVE THAT progresses slowly over time. The optic nerve, which carries messages from the eye to the brain so that you can “picture” what is around

you, consists of over one million nerve fibers. In glaucoma, these nerve fibers gradually die off, resulting in blind spots in the field of vision (area of seeing) and, in the final stage, blindness. A great deal of damage must occur before the blind spots appear. Even when they do, you usually do not notice them until they become severe. At this point, most of the optic nerve is already gone, irreversibly so. You might compare it to the invasion of a wood frame house by termites. A great deal of destruction can occur without being detected by the untrained observer. By the time the damage is noticeable, the house is on the verge of collapse. Some people have also compared glaucoma to jumping out of a ten-story window. Everything feels fine—until you hit bottom.

Many people mistakenly believe that having their eye pressure checked will tell them whether they have glaucoma. Although a high pressure of the fluid inside the eye is

the main risk factor for glaucoma, about 25 percent of glaucoma patients have what we call low-tension glaucoma. In these people, the pressure in the eye, no matter when it is checked, is always in what we consider the normal

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range. Therefore, a pressure check is most certainly not a glaucoma test, that is, a test that tells whether you have glaucoma. Not only are there many people with glaucoma who have normal eye pressures, there are also many people who have high eye pressures but who do not show any evidence of damage to the optic nerve. These individuals are said to be ocular hypertensives or glaucoma suspects. Clearly, there is much more to diagnosing glaucoma than simply checking the pressure. If that were the only test done, many cases of glaucoma would be overlooked. In practice, that is exactly what happens to many people who undergo inadequate eye examinations. Their glaucoma may become far advanced before it is diagnosed and treatment is begun.

A Careful Examination: The Key to Diagnosis

The most crucial part of the eye examination for diagnosing glaucoma is not a pressure check but a very careful examination of the optic nerve where it enters the back of the eye. In this area, the optic nerve appears as a disk, oval in shape, pinkish in color, and surrounded by the retina. This portion of the optic nerve is called the optic disk. All of the nerve fibers on the surface of the retina come together at the optic disk and then follow the optic nerve to the brain. The center of the optic disk usually

contains a craterlike area that we call the cup, which can vary greatly in size from one person to another. The first sign of glaucoma is often a change in the appearance of this cup. It enlarges and sometimes extends close to

the rim of the optic disk in one area. If the glaucoma is developing at a different rate in the two eyes, there may be a marked difference in the size of the cups in the two eyes.

The physician examining the eye notes what we call the cup/disk ratio. This is simply the distance across the cup divided by the distance across the whole optic disk. The average cup/disk ratio for normal eyes is about 0.3, which means that the distance across the cup is 30 percent (almost one-third) of the distance across the optic disk. The important thing, though, is whether a change in the size of the cup occurs over time. For this reason, we sometimes take photographs of the optic disks in people who are glaucoma suspects so

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that we will be able to detect any changes in the size of the cups. Changes in the appearance of the optic nerve often occur before any blind spots appear in a person’s field of vision.

A less common finding in glaucoma patients is a small hemorrhage (blood spot) on the surface of the optic disk. This is a strong sign that damage is occurring to the disk. Therefore, it can aid in diagnosing glaucoma as well as in determining whether the treatment being given is adequate.

It should now be apparent why careful examination of the optic nerve is the most important part of the eye examination for glaucoma. A very slight change in the appearance of the optic disk

can arouse the physician’s suspicion that glaucoma might be present, regardless of what the pressure is in the eye. Further testing and follow-up checks can then be arranged.

Visual field testing, also called perimetry, is a way of measuring the completeness of the field of vision. When we speak of the visual field, we are talking about the entire area in a person’s vision, both centrally (straight ahead) and peripherally (to the side). We often compare the visual field to a mountainous island of vision in a sea of darkness. In the periphery (side) of our visual field, corresponding to the outlying, low areas of the mountain slope, we can make out basic forms and shapes but cannot discern fine details. As we move toward the center of our visual field, climbing up the slope of the mountain toward its peak, our sharpness of vision increases, and we can soon make out every detail in the object at which we’re looking. If a trench or a crater occurs in one part of the mountain (loss of optic nerve fibers), we may not be able to see quite as well in one area, and this is what visual field testing measures.

There are two main types of perimeters (visual field testing machines). The first is the Goldmann perimeter, which has been the standard for many years. In this type of examination, the patient sits in front of a large white bowl and with his or her gaze fixed on a spot in the center of the bowl. The physician or an assistant causes a white circle of light, the size and brightness of which can be changed, to move along the bowl until the patient signals that it is visible. This process is repeated many times until the field of vision is mapped out. Goldmann perimetry (visual field testing) depends greatly on the skill and knowledge of the examiner. The perimeter is merely a tool in the examiner’s hands, much as a scalpel is a tool in the hands of a surgeon.

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