Studies Find Dangers in Extended-Wear Contacts
Extended-wear contact lenses, introduced nine years ago and now worn by 4 million Americans, are more than 10 times as likely as other kinds of lenses to cause serious eye inflammations that can lead to blindness, according to studies published today in the New England Journal of Medicine.
Scientists have long suspected that the more hours a day patients wear contact lenses, the greater the risk to their eyes, even when the lenses are prescribed for extended use. But the New England Journal studies--sponsored by the major manufacturers of contact lenses and conducted by researchers at Harvard Medical School and the Massachusetts Eye and Ear Infirmary--are the first to document the extent of the danger facing those who wear soft contact lenses overnight or longer. Those users make up about one-fifth of all contact lens wearers.
“The risk of serious eye damage with any lens is minuscule--only two-tenths of 1%,” said Barbara Kelley, director of public affairs for Bausch & Lomb, the nation’s largest manufacturer of contact lenses and one of the members of the Contact Lens Institute, which sponsored the study.
Nonetheless, Kelley said, the risk was already perceived as being significant enough that Bausch & Lomb began in April telling users of its extended-wear lenses to limit wearing time to no more than seven days, after which lenses must be removed and cleaned according to manufacturer’s directions.
In May, the U.S. Food and Drug Administration, in anticipation of the publication of the New England Journal study, advised all contact lens manufacturers to inform patients that a previous 30-day limit on wearing time should be reduced immediately to seven days.
The studies documented what is considered the worst hazard of contact-lens wear--scratching or abrasion of the cornea that can lead to ulceration, which if untreated could cause permanent damage and even blindness. Precisely what causes the increased risk of eye damage in patients who wear lenses for long periods is not clear, according to the Massachusetts researchers.
One theory is that lenses worn around-the-clock result in hypoxia, or a decreased supply of oxygen to the cells of the cornea, which in turn makes the cornea more susceptible to abrasion and infection. Another theory is that extended wear--especially if the lenses are not cleaned regularly--increases the opportunity for growth of bacteria, which can endanger the health of the eye.
People who put lenses in their eyes and leave them there are being “seduced by the convenience . . . and simply don’t take care of their lenses,” said David Krasnow, a Santa Monica optometrist who specializes in fitting contact lenses.
Indeed, the Massachusetts researchers found in a survey of ophthalmologists in five New England states and in a detailed study of 99 patients with corneal ulcers, that the overall level of lens care among both patients and control subjects was “alarmingly low.”
“It is estimated,” the editors of the New England Journal said in an editorial, “that 50% of those who wear contact lenses care for them unhygienically.” They don’t clean the lenses as prescribed. They allow mold to grow on their cleaning equipment. They pop the lenses into their mouths to wet them.
One of the reasons for poor compliance with lens-care regimens, especially among extended-wear lens users, the editors said, is that there has been too little consumer education. Manufacturers have “overemphasized the convenient and carefree aspects of using overnight lenses. . . . The trivializing of contact lenses led one prominent ophthalmologist to say: ‘We are not buying panty hose here. This is a medical device.’ ”
Contact lenses were introduced on the market in the 1940s as hard, uncomfortable glass disks about the size of a quarter. Today, contacts are about the size of a fingernail. They are made of a variety of plastic products and are worn by about 7% of the U.S. population. The safest are thought to be those that are made of hard plastic or gas-permeable rigid plastic, but they are also the most uncomfortable.
By far the easiest to wear, although the most complicated to care for, are soft lenses, introduced in 1971 and made from a variety of porous, liquid-absorbing plastics. Extended-wear soft lenses were introduced in 1981 and disposable extended-wear lenses were introduced last year.
Each type of lens has advantages and disadvantages for correcting specific vision problems and for preferences and life styles of individual patients, but some eye-care specialists have become alarmed enough by the risks associated with extended-wear lenses that they have become less eager to prescribe them.
According to the studies, about two in every 10,000 people who wear standard hard contacts will get an abrasion on the cornea that leads to an inflamed ulcer. For those who wear gas-permeable hard lenses and those who wear soft lenses and remove them every night, the risk is about four in 10,000. But for those who wear contacts around-the-clock, the risk jumps to 21 in 10,000.
The researchers found that the longer patients wore their lenses, the greater their risk of problems. But the studies did not distinguish risk rates among different brands or types of extended-wear contacts. Some eye-care specialists are hopeful that extended-wear lenses that are disposable will have fewer risks because they do not require chemicals to clean and do not build up substances that may be implicated in serious hazards to the eye.
Months before the results of the New England Journal studies were made public, ophthalmologists at the Emory University Medical School eye clinic in Atlanta said they had stopped dispensing extended-wear contacts, even though they had been early enthusiasts for the lenses.
“Most people who wear contact lenses are unaware of the more serious risks associated with them,” the editors of the New England Journal said. The chemicals used to manufacture them and disinfect them can cause allergic reactions. Dirt and grit that work their way under the lens cause scratches and scarring of the eye.
“However, the most dreaded complication is microbial ulcerative keratitis or corneal ulcer, caused by bacterial invasion of the cornea. Left untreated, this infection can quickly advance and destroy the corneal stroma, resulting in corneal perforation and even loss of vision,” the editors said.
RISKS LINKED TO SOFT CONTACTS
Contact lenses float on a layer of tears over the cornea, a raised strip of transparent tissue covering the colored iris and pupil. The smaller contact lens, which covers only part of the cornea, is known as a rigid or hard lens and is worn by about one-third of the 20 million Americans who wear contact lenses. The larger lens, which covers the cornea plus a small portion of the sclera, or white of the eye, is a soft lens. About 11 million Americans wear soft lenses that they remove daily. But another 4 million wear soft lenses specially designed to be left in the eye for up to seven days at a time--and it is this group that appears to be at greater risk of corneal ulceration. Depending on the kind of extended-wear lens, it is either sterilized and put back in the eye or replaced with a new disposable lens.
