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Cataracts
Cataracts
What is a cataract?
Cataracts are clouding of the lens portion of the eye. The result is much like smearing grease over the lens of a camera and impairs normal vision. 
Cataracts will affect 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.
Experts estimate that over 1.2 million Americans are diagnosed annually with cataracts that require treatment. As their is are growing numbers of elderly in the United States, the incidence of cataracts is increasing. These persons often want to continue driving cars, reading and traveling-activities for which clear sight is vital.
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 hourlong 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 does a cataract form?
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 UV 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. (See "Shielding Your Eyes from the Sun" below).
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.
What are the symptoms of cataracts?
Symptoms of developing cataracts include double or blurred vision, sensitivity to light and glare (such as bright sun or auto headlights), less vivid perception of color, and frequent changes in eye-glass 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.
How are cataracts diagnosed?
Cataracts are typically detected through a medical eye examination. The doctor can see the abnormal lens using a hand-held viewing instrument (ophthalmoscope). 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.
What are the 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, eye-glasses 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.
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.
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.
What is the procedure for implantation of an IOL?
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.
There are three types of surgery to remove lenses that have a cataract: - Extracapsular surgery. The eye surgeon removes the lens, leaving behind the back half of the capsule (the outer covering of the lens).
- Phacoemulsification (pronounced FAY-co-ee-mul-sih-fih-CAY-shun). In this type of extracapsular surgery, the surgeon softens the lens with sound waves and removes it through a needle. The back half of the lens capsule is left behind.
- Intracapsular surgery. The surgeon removes the entire lens, including the capsule. This method is rarely used.
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.
Some manufacturers are also developing bifocal IOLS, which may eliminate the need in some patients for prescription glasses after surgery.
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; wrap-around sunglasses are recommended during the day.
What happens after the IOL procedure?
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.
At a time when more older Americans than ever before are looking forward to years of active life ahead of them, IOLs clearly offer hope and a better life.
Why should I shield my eyes from the sun?...Prevention
Headed for the ski slopes or beach? These pleasures can pose dangers to your eyes unless you take precautions against the sun's harmful rays.
Ultraviolet radiation is invisible and cannot be felt, yet long-term exposure to it may be associated with development of cataracts. Short-term exposure to very intense ultraviolet light- such as you get on a ski slope-can produce photokeratitis, also called actinic keratopathy or snow blindness. There is even some evidence ultraviolet radiation may damage the eye's retina.
By spring of 1990, a new voluntary labeling program developed by the Sunglass Association of America in cooperation with the Food and Drug Administration is expected to be in place to tell consumers how much UV protection they can expect from nonprescription sunglasses. (Prescription sunglasses already meet standards of protection against UV radiation and are not included in this labeling program.)
The voluntary labeling program calls for manufacturers to attach a tag to sunglasses that specifies the level of protection from the two types of ultraviolet rays: the longer wavelength ultraviolet A (UVA) radiation and the shorter wavelength ultraviolet B (UVB) rays. The standards were developed in 1986 by the American National Standards Institute in New York City through consultation with eye-care professionals and educators, research scientists, industry, and military and other government agencies. The labeling standards are the only recognized statement on the properties and performance of sunglasses.
The different categories describe minimum levels of protection and are designed to help consumers pick the best glasses for the types of activities they plan: - Cosmetic: For non-harsh sunlight and around-town uses such as shopping. These will block at least 70 percent of UVB, 20 percent of UVA, and less than 60 percent of visible light.
- General Purpose: For most outdoor activities such as boating, flying, hiking, picnicking, and beach outings. They also can be used for snow settings. They will block at least 95 percent of UVB, at least 60 percent of UVA, and from 60 to 92 percent of visible light.
- Special Purpose: For very bright environments such as tropical beaches and ski slopes and for activities like mountain climbing. They will block at least 99 percent of UVB and 60 percent of UVA, in addition to from 20 to 97 percent of visible light.
The amount of visible light-glare blocked by sunglasses depends on the darkness of the lenses. The darker shades of special- purpose sunglasses are intended for a high level of brightness, while the lighter shades can be used for less bright situations-like skiing on a cloudy day.
In addition, within the categories, look for the actual percentage of the sun's UV radiation that each particular model of glasses claims to block. The greater the blockage, the lower the risk of UV damage to the eye.
Thomas Loomis, technical director of the Sunglass Association of America, offers this advice when buying non- prescription sunglasses:
First, decide on the purpose, color and fashion you want. Once you've made a selection, hold the sunglasses up at arm's length and look through them at an object with a straight border, such as a window or door frame. Move the glasses slowly across the line. If it seems to wiggle, sway or curve, the lenses contain an optical defect and should be replaced with another pair.
Since 8 percent of males and 3 percent of females have a vision color defect, be sure the glasses don't distort the colors of a traffic signal. Pay for the glasses, says Loomis, walk outside the store and conduct your own test. If they distort the colors, exchange them for another pair. - Cataracts will affect most people if they live long enough.
- Symptoms of cataracts include double or blurred vision and sensitivity to light and glare.
- Cataracts can be diagnosed when the doctor examines the eyes with a viewing instrument.
- The ideal treatment for cataracts is surgical implantation of a new lens.
- Sunglasses can help to prevent cataracts.
This article is in part based in information from the U.S. Food and Drug Administration (FDA).
Last updated on 05/15/2008
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