Cataract surgery

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Figuratively speaking, age may help us to see things more clearly. Literally, it has the opposite effect. By mid-life, the lenses of our eyes have cloudy patches; by age 65, 95% of us have some degree of cataract. Moreover, for reasons that aren't well understood, cataracts occur 13% more frequently in women than in men. While the majority of people can live with their cataracts, surgery has become a ready option for those with significant visual impairment. New equipment and surgical techniques, as well as widespread acceptance by insurers, have made cataract extraction one of the most widely performed and least risky operations today.

What is a cataract?
The lens is a convex structure that helps to focus light onto the retina, where an image is formed; it is uniquely equipped for the task because it is composed of transparent cells. Like other body cells, those in the lens begin life crammed with tiny structures called organelles that take care of maintenance and housekeeping. As these cells mature, they shed all of their organelles, leaving only crystalline proteins.

Like the skin and many other tissues, the lens acquires new cells on the surface throughout life. However, the older lens fiber cells do not slough off as skin cells do, but migrate into the center of the lens. Over a lifetime, the components of the long-lived cells are subject to a variety of oxidative reactions, both from processes within the body and from environmental sources. These reactions, which are similar to those that turn iron to rust, break down the crystalline lens proteins. The proteins coagulate, giving the cells an opaque, yellowish appearance. When these cloudy cells block the transmission of light enough to disturb vision, a person is said to have a cataract.

People who have cataracts are often bothered by glare caused by scattered light -- an effect akin to that of looking at automobile headlights through a dirty windshield. Images may be blurred, especially at close range. Cataracts may also distort images by making straight edges appear wavy or curved. The yellowed lens may alter color perception.

Who gets cataracts?
Time alone increases the likelihood of developing cataracts. Smoking, drinking alcohol, and taking corticosteroid medications also add to the risk. Exposure to ultraviolet light from hours in the sun and ionizing radiation, principally from gamma rays and x-rays that are used in medical diagnosis and treatment, have also been shown to cause cataracts. On the other hand, microwave radiation, though linked with cataracts in the laboratory, has not been demonstrated to cause cataracts in humans. Certain conditions, such as diabetes, obesity, and hypoparathyroidism are associated also with increased risk.

Cataract extraction
The only effective treatment at present for cataracts is surgical extraction. There are several ways to remove a cataract. In the past, both the lens and the clear capsule that holds it in place were removed. This so-called intracapsular procedure has been largely replaced by extracapsular extraction, in which the capsule is retained. The capsule helps to protect the retina and to support an artificial lens, which is usually placed during the operation.

During extracapsular extraction, the ophthalmologist makes a small, 1/3-1/2-inch incision in the white part of the eye. Using a microscope to magnify the operating field, he or she cuts away the center, or nucleus, of the lens. Gently pressing the eye with special instruments, the ophthalmologist expresses the nucleus through the incision. (See illustration.) Then the remainder of the lens is sucked up through a tiny vacuum tube and the area is irrigated.

Once the natural lens is removed, the eye loses a large portion of its ability to focus light rays, so a plastic intraocular lens implant (IOL) is placed inside the eye. The wound may be stitched with several tiny sutures. Occasionally, an IOL cannot be placed during surgery, and may be inserted in a subsequent operation or a contact lens can be fitted.

A newer technique, phacoemulsification, employs ultrasound energy to dissolve the lens so it can be vacuumed up, as shown on next page. This procedure can be performed through a much smaller incision -- only about 1/8 inch. A foldable IOL developed for use following phacoemulsification is inserted through the incision and re-expands inside the eye. Because the incision is so small, the wound heals faster. When a standard IOL is used following phacoemulsification, the incision must be expanded.

Complications of cataract surgery, especially with the newer techniques and improved IOLs, are uncommon. When they do occur, the most frequent are infection, bleeding within the eye, blocked blood vessels, glaucoma, loss of corneal clarity, inability to dilate the pupil, dislocation of the IOL, retinal detachment, and swelling of the macula -- the area of the retina responsible for central vision.

What to expect
Only cataracts that significantly disrupt vision require treatment. When there is also an abnormality in another part of the eye -- for example, the cornea or retina -- as well as a cataract, lens extraction may not correct the problem. Therefore, if you have a cataract, it is important to determine whether your sight is diminished enough to warrant surgery and whether the cataract alone is responsible for most of the problem.

The ophthalmologist uses a number of tests to make these determinations. He or she usually begins with the familiar Snellen chart that contains letters of decreasing size to measure visual acuity in both light and darkness. The next step is a thorough eye exam with an ophthalmoscope as well as a slit lamp, which combines a microscope and a special light source. This exam can determine the location and extent of the cataract, as well as rule out diseases in other parts of the eye that may contribute to impaired vision. In addition, the ophthalmologist will test for glaucoma, also a common cause of diminished visual acuity, by measuring intraocular pressure. He or she will also use specialized ultrasound equipment to measure the length of the eye to determine the power that the IOL should have and, occasionally, to "see" behind an opaque cataract.

Once you have decided to undergo surgery, you should see your primary-care clinician for a pre-operative physical exam to determine whether you have any conditions that may increase your risk of complications from surgery. Your ophthalmologist may require blood tests and an electrocardiogram prior to surgery. You should not eat or drink after supper the night before surgery, but can take your regular medications with water the next morning.

Cataract surgery may be performed in a day surgical unit or a free-standing ambulatory surgical center. Only patients who have serious underlying medical conditions require overnight hospitalization.

Just prior to surgery, an intravenous (IV) catheter will be placed in your arm and heart monitors applied. You will probably be given a sedative to relieve anxiety. Topical drops may be placed on your eye to anesthetize it, or you may receive an injection below your eye to numb it. During surgery, your head may be taped to the table to stabilize it. The operation usually takes about 30 minutes.

If local anesthesia is used, you should be able to eat, drink, and walk about shortly after surgery. You must arrange for someone else to drive you home afterward, and you should rest at home for the remainder of the day.

You will be given antibiotic and steroid eyedrops to diminish inflammation, prevent infection, and moisten the eye after surgery. You should avoid touching or rubbing your eye, and you may be asked to wear an eyeshield at night for 2 to 3 weeks. You may be advised to wear UV-protective lenses to reduce glare from outdoor light.

You should be able to resume most of your activities within a day or two of surgery, but should avoid strenuous exercise and heavy lifting, at least for the first several weeks. You may need to take medications to prevent constipation, coughing, or wheezing, which put pressure on the eye. If you have a sedentary job, you can be back to work in a week.

If your surgery was performed with topical anesthesia, you should have some useful vision immediately after the operation, but full recovery takes several weeks. If you have had an injection below the eye, you will wear a patch for a day. After 4-8 weeks, when the surgical wound has healed sufficiently, your ophthalmologist will test your vision. Even though you have received a new lens, you will probably need eyeglasses to further correct your vision. Your eye may continue to heal over the next few months, and your eyeglass prescription may need to be modified.

Cataract prevention
There are no proven strategies for preventing cataracts in healthy adults. For diabetics, controlling blood glucose levels reduces the rate and extent of cataract formation. If you're taking medications containing steroids for asthma or inflammatory diseases, talk to your doctor about minimizing the dose. Protect your eyes from UV radiation by wearing protective sunglasses outdoors. Drink alcohol only in moderation. If you smoke, stop.

Scientists are still looking for medical therapies to delay or prevent cataract formation. Among the most promising are the antioxidant vitamins, which appear to retard cataract formation in animals. However, they have not been demonstrated to have similar effects in humans. For now, it makes sense to follow the National Research Council's advice and consume one's antioxidants by eating five servings of fruits and vegetables a day.

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