Lifting the clouds of cataracts


You're approaching retirement, feeling healthy and looking forward to many more active and productive years. But then your vision begins to grow cloudy. Everything you look at has a yellowish tint. Simple tasks like reading or driving a car become difficult. Street signs and faces aren't as sharp as they once were. Bright sun and auto headlights hurt your eyes. New eyeglass prescriptions improve vision for a while -- but eventually they no longer help.

The culprit is cataracts, a condition that will beset most people if they live long enough. This disorder affects 60 percent of people older than 60 and occurs when the normally clear, aspirin-sized lens of the eye starts to become cloudy, impairing vision.

Until recently, anyone who developed cataracts and needed surgery faced a procedure that involved pain and often less than satisfactory results. Until the late 1970s, doctors removed the cloudy lens in a surgical procedure that required a hospital stay of five to seven days. Afterward, the patient had to wear thick "Coke bottle" glasses or contact lenses -- neither of which could completely restore vision to its previous level.

Today, there's little need for such complicated treatment. Advances in medicine have made cataracts much less worrisome. Now, the clouded lens is surgically removed and replaced with a plastic intraocular lens (IOL) in an hour-long operation that often requires no hospitalization.

"The intraocular lens has revolutionized the treatment of cataracts," says Carl Kupfer, M.D., director of the National Eye Institute in Bethesda, Md. "Implantation of the lens is one of the most successful operations in medicine."

How a Cataract Forms
A cataract forms in the eye's lens, the transparent structure behind the iris (the colored membrane surrounding the pupil). The lens focuses light on the retina, the light-sensitive membrane at the back of the eye which converts light impulses into nerve signals to produce clear visual images. Clouding of the lens -- much like smearing grease over the lens of a camera -- can develop at any age but most often appears in people older than 42.

Most cataracts are caused by a change in the chemical composition of the lens. In a small percentage of cases, the chemical changes are caused by a hereditary enzyme defect, trauma to the eye, diabetes, or use of certain drugs, such as the steroid prednisone.

Precisely why cataracts occur with age is unknown, but ultraviolet radiation, particularly from the sun, is thought to play a major role in creating the chemical change in the lens responsible for most cataracts. Experimental evidence suggests that ultraviolet radiation can cloud the lens by forming highly reactive chemical fragments called "free radicals." These, in turn, disrupt the delicate structure of the lens. The type of ultraviolet radiation from the sun called UVB -- the kind that causes blistering sunburn and skin cancer -- is thought to be a major factor because the lens absorbs these rays.

Indeed, in a study of 838 Chesapeake Bay professional fishermen, Hugh Taylor, M.D., of Johns Hopkins Hospital in Baltimore, Md., found a strong association between ultraviolet radiation and cataract formation. Fishermen with the highest levels of ultraviolet radiation exposure had three times the risk of contracting cataracts compared with those with the least exposure. Those with cataracts had 20 percent more exposure to sunlight in every year of life. Taylor's studies suggest that cataracts can be prevented by avoiding sun exposure between 10 a.m. and 4 p.m., when sunlight is strongest, and by wearing a wide-brimmed hat and sunglasses.

A cataract can develop so slowly that a person may not even know it's there. If the cataract is on the outer edge of the lens, no change in vision may be noticeable. Cloudiness near the center of the lens, however, usually interferes with clear sight.

Symptoms of developing cataracts include double or blurred vision, sensitivity to light and glare (which may make driving difficult), less vivid perception of color, and frequent changes in eyeglass prescriptions. As the cataract grows worse, stronger glasses no longer improve sight, although holding objects nearer to the eye may help reading and close-up work. The pupil, which normally appears black, may undergo noticeable color changes and appear to be yellowish or white, says Peter Hersh, M.D., an assistant surgeon at Boston's Massachusetts Eye and Ear Infirmary.

Cataracts are typically detected through a medical eye examination. The usual test for visual acuity, the letter eye chart, may not, however, reflect the true nature of visual loss, says the American Academy of Ophthalmology. Other tests -- which measure glare sensitivity, contrast sensitivity, night vision, color vision, and side or central vision --help nail down the diagnosis.

Because most cataracts associated with aging develop slowly, many patients may not notice their visual loss until it has become severe. Some cataracts remain small and never need treatment; others grow more quickly and progressively larger. Only when a cataract seriously interferes with normal activities is it time to consider surgery, doctors say. People who depend on their eyes for work, play and other activities may want their cataracts removed earlier than those whose needs are less demanding.

Some experts estimate that about 88 of every 100 persons receiving IOLs will achieve 20/40 vision or better. (An individual with 20/40 vision can read letters on an eye chart from 20 feet away, while a person with normal 20/20 vision can read the chart from 40 feet away; 20/40 vision is good enough to get a driver's license in most states.) Among those who do not have other eye diseases, about 94 of 100 will achieve 20/40 vision.

Treatment Options
During the diagnostic examination, an ophthalmologist will carefully measure the shape, size and general health of the eye to determine whether a lens implant will be effective. In the relatively small number of cases where it won't be, eyeglasses or contact lenses will improve vision after traditional cataract surgery. Glasses, while used for years, have drawbacks. Their extreme thickness makes them unattractive and heavy. Magnification and distortion of the visual image causes objects to appear closer and 25 percent larger than they are. Peripheral vision may be reduced. Contact lenses provide fairly good vision, but many elderly people have trouble inserting, removing and cleaning them.

An implanted IOL is usually the best replacement. Because the implant is placed in or near the original position of the removed natural lens, vision is restored with good peripheral vision and depth perception yet with minimal magnification and distortion.

Getting an IOL
IOLs remain permanently in place, require no maintenance or handling, and are neither felt by the patient nor noticed by others. Eyeglasses with thin lenses for near or distant viewing may still be required, but thick glasses are not necessary. A doctor can determine the appropriate implant prescription with an ultrasound device that measures eye length and corneal curvature. These measurements are combined by computer to calculate the lens power required.

The standard surgical procedure, which ranges in cost from $3,000 to $5,000, is performed in a hospital or doctor's office. Peering through an operating microscope, the surgeon makes a minute, curved incision in the cornea -- the surface of the eye. Then the clouded lens is cut loose with a thin needle and suctioned out, leaving intact the rear wall of the transparent capsule that encloses the lens.

The surgeon enlarges the original incision, and the new lens -- a clear hard plastic disc -- is then slipped in behind the iris and up against the back wall of the capsule. Two tiny "c" shaped arms attached to the lens eventually become scarred into the side of the eye and hold the lens firmly in place. The incision is closed with 7 to 10 nearly invisible stitches of fine nylon or silk.

In a newer method, an ultrasonic probe enters the cut in the cornea and high-speed vibrations break the lens into microscopic flecks that are then removed by suction. A folded flexible plastic lens one-quarter of an inch in diameter can be inserted through the cut with a scissors-like device called an injector and positioned behind the pupil against the capsule wall. Once in place, the injector is removed and the lens opens.

The procedure to remove the natural lens and replace it with a synthetic one is done under a general or local anesthesia with injections made in muscles around the eye. Recovery takes several hours in the hospital; in a few cases, it may require an overnight stay. The patient wears a metal shield over the eye. at night; wraparound sunglasses are recommended during the day.

Within a few days of the operation, most people are back at work. In several office visits during the first six to eight weeks after surgery, the doctor will check for infections or other complications and fit the patient for reading glasses. Vision is significantly improved in 95 to 98 percent of cases.

However, results of the operation aren't always worry free. After the IOL implantation, a clouding of the lens capsule, known as a "secondary cataract," occurs in roughly 40 percent of cases. To restore vision, a pulsed yttrium, aluminum, garnet (YAG) laser is used to produce a hole non-thermally, by "optical breakdown," in the capsule to allow the normal passage of light rays back to the retina. This painless procedure takes a few minutes; improvement usually is immediate. Other problems that may occur in a small percentage of patients include swelling of the cornea, glaucoma, and swelling of the retina, which distorts vision. Overall, though, IOLs "have turned out to be much better than anyone ever expected," says Nancy Brogden, chief of the Food and Drug Administration's IOL branch.

DIAGRAM: IOL Implantation; In IOL Implantation, the clouded natural lens (diagram on left) is removed and replaced by an implanted lens (diagram on right).


by Ellen Hale

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