Harvard Health Letter
Each of our eyes comes equipped with a lens tucked behind the pupil that focuses light on the retina in the back of the eye. When we're young, those lenses are quite clear. But with age and exposure to light and other harmful factors, they have a tendency to cloud up, as the proteins in the watery mixture inside the lens clump up. Clouding of the lens is called a cataract.
Cataracts are typically small to begin with and in the center of the lens. Both lenses tend to be affected, although often one is more clouded than the other. Symptoms include blurry vision and difficulty with glare at night.
In many cases, there's an increase in nearsightedness well before there's any detectable clouding of the lens. This "myopic shift" can be treated with a new prescription for glasses or contact lenses that correct the change in vision.
Cataracts tend to get worse and, if left untreated, can result in blindness. In the poorer countries of the world, untreated cataracts are a leading cause of blindness. But elsewhere, as the lens gets cloudier and vision problems increase, surgery prevents that from happening. The procedure typically involves removing the clouded lens and replacing it with an artificial one made of clear plastic.
Cataract surgery is now one of the most common, safest, and most effective operations performed in the United States. It's usually performed on an outpatient basis and with local anesthesia. According to government health statistics, about 20 million Americans -- 17 percent of those 40 and older -- have a cataract in one or both eyes, and about 6 million (5.1 percent of this age group) have had cataract surgery.
WILL LASER SURGERY BE WORTH THE EXTRA COST?The lens is surrounded by a thin, envelope-like capsule. Currently, most cataract surgery involves making an incision in the capsule, using ultrasonic energy to break up the lens into small pieces, and then vacuuming those pieces out so a new artificial lens can be put back into the capsule.
Ophthalmologists have been using high-speed lasers for some time to perform the LASIK procedures that reshape the cornea so that people no longer need to wear glasses. Now some are using similar technology to perform cataract surgery. Very fast femtosecond lasers -- a femtosecond is one quadrillionth of a second -- are used to open up the capsule and to break up the lens.
Proponents say these lasers, which are guided by computers, will make cataract surgery that much safer for two reasons: The incisions are more precise, and lower levels of ultrasonic energy are needed to break up the lens because the laser softens them up. These computer-assisted lasers can make a perfectly circular incision in the capsule that his trained hand cannot match, notes Dr. Bradford J. Shingleton, an associate clinical professor at Harvard Medical School and a prominent Boston eye surgeon who specializes in cataracts.
But, so far, these are just claims without a great deal of quality evidence to back them, and nothing remotely close to the results from a large, well-designed clinical trial that would be definitive. Still, Shingleton says laser surgery could potentially be one of those technologies that sweeps away old techniques and the equipment used to perform them.
One question, though, is whether the technical improvements in the operation will translate into significantly better outcomes. There isn't that much room for improvement, Shingleton says. "You are taking an A-plus operation and maybe making it an A-plus-plus operation."
But say there are better outcomes. Then the question becomes whether they are worth the additional cost. How much pricier the laser cataract surgery will be than conventional cataract surgery is hard to say at this point. But the laser setups are expensive, and the ophthalmology practices that buy them will have to recoup their investment.
Another big unknown is whether Medicare and other insurance will provide coverage. Right now, surgeons can't charge Medicare extra for doing cataract surgery with a laser. Until they can, laser cataract surgery may be slow to catch on.
Once cataract-damaged lenses are removed, several different types of artificial ones can be used to replace them. Here are some of the choices:
Monofocal lenses As the name suggests, monofocal lenses are designed to focus at one set distance. Shingleton says they are a "no brainer" for cataract patients whose primary concern is clear, sharp vision. You can try the monovision approach: a replacement lens calibrated for distance vision is implanted in one eye and a lens set for near vision implanted in the other eye. The brain learns how to process the visual information so you may no longer need to wear glasses. But there is an adjustment period, and some people continue to have some difficulty, so monovision isn't for everybody.
Monofocal lenses are the least expensive choice among the lenses. Medicare pays for cataract surgery, but caps coverage of the lenses; only monofocal lenses are fully covered.
Toric lenses Toric lenses are shaped to compensate for astigmatism and the football-shaped cornea that causes it. They may not completely correct astigmatism, so people still need to wear glasses, but there's enough of a correction so most people notice they can see much better without glasses. Shingleton says he is a "real believer" in toric lenses and views them as a major advance in cataract surgery. They do carry a higher cost that may not be covered by Medicare or other health insurance.
Accommodating lenses Accommodation is the ophthalmic term for the ability of the eye's own lens to change shape so we can change focus, seeing up close and far away. Accommodation tends to decline with age. In 2003, the FDA approved the Crystalens replacement lens, which is supposed to emulate the flexible, accommodating natural lenses of younger eyes. The Crystalens has hinges on its sides, so the contraction and relaxation of the muscles in the ciliary body of the eye can change the position of the lens.
Crystalens lenses give patients excellent distance vision, but they are not proving to be quite as good for near vision, so some patients who get them end up needing to wear reading glasses, according to Shingleton.
Cost is an issue, also. A Crystalens lens is between $2,000 and $3,000 more expensive than a monofocal lens, and Medicare doesn't cover the additional expense.
Multifocal lenses Similar to the bifocal or progressive lenses used in glasses, some areas of the multifocal lens are for distance vision, and others are for intermediate and near vision. But unlike the lenses in glasses, the different areas are organized in concentric circles, rather than from top to bottom. The two main brands on the market are Restor and Tecnis. The major drawback of the multifocal lenses is that they sometimes make it more difficult to see at night. The tiny ridges in the lenses can distort bright light, so there's glare and a halo effect. However, Shingleton says most people's eyes (and brains) adapt so they don't notice much of a problem. In general, he says, the quality of the vision is not quite as sharp with the multifocal lenses as it is with monofocal lenses.