Keeping an Eye on Contact Lenses
Safety, Options Shape Contact Lens Decisions
by Dixie Farley
Imagine wearing your contact lenses for a few hours and then, after you pop
them out, still seeing clearly for a portion of the day. For certain individuals
with nearsightedness, that image can be reality, thanks to a new lens the Food
and Drug Administration recently cleared for marketing.
The OK rigid gas-permeable contact lens, made by ConTEX, Sherman Oaks,
Calif., is the first lens designed to correct nearsightedness by temporarily
reshaping the transparent tissue known as the cornea that covers the iris and
pupil. It is just one of many choices for the 28 million Americans who wear
contact lenses.
These medical devices, sold under more than 350 brand names, offer numerous
options, including rigid-lens handling ease, soft-lens comfort, bifocal vision,
a rainbow of colors, no-fuss disposables, and even protective help against
ultraviolet radiation.
Shaping Up
The idea behind the OK lens is not new. Since the early 1960s, some
optometrists have used conventional daily-wear rigid lenses to reshape corneas.
This procedure is called orthokeratology, or Ortho-K. FDA considers such
treatment of an individual patient to be the practice of medicine and therefore
not subject to regulation. Selling contacts not cleared for Ortho-K to
practitioners for this use is illegal marketing, however, so the agency is
helping manufacturers obtain clearances specifically for Ortho-K. (See "Buyer
Beware.")
Studies before FDA began regulating contact lenses, in 1976, show that
Ortho-K appears to be safe, says James Saviola, O.D., chief of the vitreoretinal
and extraocular devices branch at FDA's Center for Devices and Radiological
Health. "The lower your amount of nearsightedness, the greater your
probability of success with Ortho-K," he says.
Ortho-K reshaping involves the use of a series of lenses that apply pressure
to the cornea. Once the desired result is achieved, use of daily-wear
maintenance lenses is crucial to retain the reshaping. If you wear the
maintenance lenses faithfully, Saviola says, "you may only need to wear the
lenses for a portion of the day."
However, Ortho-K does not work for everyone. Some people do not experience
any significant reduction in nearsightedness. "An individual's response is
difficult to predict," Saviola says. "It may take weeks or months to
have an effect."
Safety Concerns
The most serious safety concern with any contact lens is related to overnight
use. Extended-wear (overnight) contact lenses--rigid or soft--increase the risk
of corneal ulcers, infection-caused eruptions on the cornea that can lead to
blindness. Symptoms include vision changes, eye redness, eye discomfort or pain,
and excessive tearing.
The risk of corneal ulcers for people who keep extended-wear lenses in
overnight is 10 to 15 times greater than for those who use daily-wear lenses
only while awake, says James Saviola, O.D., chief of the vitreoretinal and
extraocular devices branch at FDA's Center for Devices and Radiological Health.
When the eyes are open, he explains, tears carry adequate oxygen to the
cornea to keep it healthy. But during sleep, the eye produces fewer tears,
causing the cornea to swell. Under the binding down of a rigid contact lens
during sleep, the flow of tears and oxygen to the cornea is further reduced.
This lack of oxygen leaves the eye vulnerable to infection.
Extended-wear rigid lenses also can cause unexpected, sometimes undesirable,
reshaping of the cornea.
Soft extended-wear lenses also bind down on the closed eye, but they are
porous and allow some tears through during sleep. Because they have so little
form, their binding has little effect on the shape of the eye.
FDA has approved extended-wear lenses for use up to seven days before removal
for cleaning. Still, there are risks with use of extended-wear lenses,
"even if it's just one night," Saviola says. Daily-wear lenses are
removed daily for cleaning and are a safer choice, provided they aren't worn
during sleep.
Another sight-threatening concern is the infection Acanthamoeba keratitis,
caused by improper lens care. This difficult-to-treat parasitic infection's
symptoms are similar to those of corneal ulcers.
The use of homemade saline from salt tablets is one of the biggest
contributors to Acanthamoeba keratitis in contact lens wearers. "FDA no
longer condones the use of salt tablets, and neither should a concerned
pharmacist," writes Janet Engle, Pharm.D., in the 1996 Handbook of
Nonprescription Drugs. Engle is associate dean for academic affairs and clinical
associate professor of pharmacy practice at the University of Illinois in
Chicago.
Microorganisms may also be present in distilled water, so always use
commercial sterile saline solutions to dissolve enzyme tablets. Heat
disinfection is the only method effective against Acanthamoeba, and it also
kills organisms in and on the lens case. (See "Proper
Care Gives Safer Wear.")
The Options
Soft lenses are much more comfortable than rigid lenses, thanks to their ability
to conform to the eye and absorb and hold water. You can get used to soft lenses
within days, compared with several weeks for rigid. An added benefit is that
soft lenses aren't as likely as rigid lenses to pop out or capture foreign
material like dust underneath. Extra-thin soft lenses are available for very
sensitive people.
While the ability to hold water increases oxygen permeability of soft lenses,
it increases their fragility as well.
Rigid lenses generally give clearer vision. They can be marked to show which
lens is for which eye. They don't rip or tear, so they're easy to handle.
Also, rigid lenses don't absorb chemicals, unlike soft lenses, which Saviola
says are like sponges. "They'll suck up any residues on your hands--soap,
lotion, whatever."
Both soft and rigid lenses offer bifocal correction. In some models, each
lens corrects for near and distance vision. In others, one lens is for near
vision, and the other is for distance. Middle-aged people who have good distance
vision but need help for reading can get a monovision reading lens for one eye.
Soft lenses additionally come as disposable products (defined by FDA as used
once and discarded) or as planned-replacement lenses.
With planned-replacement lenses, the practitioner works out a replacement
schedule tailored to each patient's needs, says Byron Tart, director of
promotion and advertising policy at FDA's devices center. "For patients who
produce a higher level of protein in their eyes or don't take as good care of
their lenses, it might be healthier to replace the lenses more frequently,"
he says.
Some practitioners prescribe disposables as planned-replacement lenses, which
are removed, disinfected and reused before being discarded. Saviola cautions
that lenses labeled "disposable" don't come with instructions for
cleaning and disinfecting, while those labeled specifically for planned
replacement do. Whatever lenses your practitioner prescribes, be sure to ask for
written instructions and follow them carefully.
In the U.S. contact lens marketplace, 82 percent wear soft lenses, 16 percent
wear rigid gas-permeable, and 2 percent wear hard. Although very few people wear
hard lenses, they are available for people who have adapted to them and want
them. Hard lenses are not the same as rigid gas-permeable lenses, since they do
not allow oxygen transmission through the lens.
Contacts Not for Everyone
People with inadequate tearing (dry eye syndrome) usually can't tolerate
contacts, says Donna Lochner, chief of the intraocular and corneal implants
branch of FDA's devices center. In addition, Lochner says, "Severe
nearsightedness often can't be corrected effectively with contact lenses."
Saviola notes that certain working conditions, such as exposure to chemical
fumes, may be undesirable for contact-lens wearers. Contacts may be ruled out by
allergy to lens-care products or by corneal problems, such as a history of viral
infection of the cornea. "Extra caution," he says, "should be
exercised with diabetics, because they're susceptible to infection and have
trouble healing."
Cosmetic use of contacts is limited in children. Adolescence is the youngest
age as a rule to consider contact lenses, says Saviola, but some practitioners
do fit 9- to 11-year-olds. "You may prescribe for a younger child who has
the motor skills and responsibility to handle contact lenses."
For some people who haven't been able to wear contacts and want to,
implantable lenses may be an option in the future.
Doctors are studying ring segments, "shaped like parentheses,"
Lochner says, which are implanted in the cornea. "They flatten out the
cornea, changing the shape to give the correct optical power." Lenses that
are implanted inside the eye are also being studied to correct refractive error,
she says.
Correcting vision is not the only use for contact lenses.
Some soft contacts are used as bandage lenses after photorefractive
keratectomy laser surgery for nearsightedness. The surgery removes the outer
cell layer of the cornea, creating a large abrasion on the eye. "It's
excruciatingly painful," Saviola says, "if you don't have a protective
covering on the cornea after the anesthetic wears off."
Collagen eye shields are used as bandage lenses to relieve pain from other
abrasions or sores on the cornea. They dissolve in a couple of days.
Comparison Shopping
Companies that sell contact lenses compete stiffly for business, offering
discounts and premiums such as a second set free.
But a discount for the lenses might not save you money if the price doesn't
include other needed products and services, such as a thorough eye examination,
lens-care kit, and follow-up visits to make sure you're adapting. A moderate
cost for a package that has everything you need may be the best deal.
Before you make an appointment, ask the practitioner these questions:
