Patient Management
Continuous Wear: a Question of Safety
Today's new silicone hydrogel contact lenses have come remarkably close to eliminating the problems of the past.
By Susan J. Taub, M.D., F.A.C.S.

Once bitten, twice shy. Given all the problems surrounding use of the original extended-wear lenses of the 1980s, it's understandable that some ophthalmologists are wary of the new generation of extended-wear contact lenses. The new lenses, however, are very different from -- and far more advanced than -- the lenses of the '80s.

New lenses, new name

The new lenses go by a new name: continuous wear. Is the name change justified, or is it just a marketing ploy? Is it possible that we'll find out, as we did in the 1980s, that overnight wear means taking unacceptable safety risks? Will it turn out that optimal safety requires more frequent contact lens removal and replacement?

We don't know for sure, but the good news is that even some of ophthalmology's most skeptical and conservative clinicians and researchers have confirmed the wisdom of the FDA's recent approval of CIBA Vision's Focus NIGHT & DAY lenses and Bausch & Lomb's PureVision lenses for up to 30 days and nights of wear.

The FDA and the two manufacturers were neither quick nor cavalier about introducing these lenses. The amount of research devoted to them is impressive.

Novartis says it spent more than $100 million to develop its lens, which is now prescribed in more than 42 countries worldwide. According to Novartis, by the time of its FDA submission, NIGHT & DAY was the best researched contact lens in the world. Adding to that mountain of data was Bausch & Lomb's research. (In fact, it was the industry trade organization, the Contact Lens Institute, that funded the Harvard University research that established the safety risks of the original extended-wear lenses and caused their market demise.)

Demonstrating safety

In 1986, at the height of the extended-wear scare, researchers were trying to figure out why extended-wear patients had a higher prevalence of microbial keratitis (MK). Extended wear seemed to increase the rate of bacterial binding, which is a risk factor for MK. Most researchers thought that lens disposability would solve this problem, but even today, half of the contact lens wearers diagnosed with MK are daily-wear patients.

What researchers discovered is that pseudomonas binds preferentially to damaged sections of the epithelium. The link to the contact lenses turned out to be oxygen permeability; insufficient oxygen can cause epithelial degradation.

The new lenses have largely resolved this issue. Testing has demonstrated that high-Dk materials, because of their excellent oxygen transmissibility, don't cause epithelial degradation or its accompanying risk of increased bacterial binding. Lenses with a Dk/t of 125 limit overnight corneal edema to 3.2 percent; NIGHT & DAY lenses have a Dk/t of 175.

In fact, when comparing patients wearing high-Dk materials continuously for 6 nights to patients wearing NIGHT & DAY lenses continuously for up to 30 nights, the data reportedly are indistinguishable. Moreover, research suggests that with "super-Dk" materials, the risks actually decrease over time.

Here are some other noteworthy statistics:

• According to the Cooperative Research Centre for Eye Research and Technology in Sydney, Australia, about 350,000 people around the world wear high-Dk lenses. So far, 13 cases of microbial keratitis have been reported among these patients. Although zero cases would be ideal, 13 cases out of 350,000 wearers is 38 times lower than the rate of MK cases found among low-Dk lens wearers.
• In Australia, about 52,000 contact lens wearers currently wear a high-Dk lens. Out of these patients, we know of four cases of MK. (Final data is still missing regarding one more suspected case). Three of these patients developed the problem after swimming in the ocean. Also, three of them cultured positive, but not with pseudomonas. Two of the cases resolved with 20/25 vision and two resolved with no effect on vision.
• According to the Australian center, the chance of losing significant vision (i.e., losing two lines) is about one in 40,000 for daily-wear patients, one in 12,000 for extended-wear patients, and one in 32 for LASIK patients.

The compliance factor

I sleep better at night knowing that my patients who want to sleep in their contact lenses can now do so safely with these new products. That safety is crucial because, despite endless warnings, I know that some patients won't comply with prescribed wearing regimens. If a patient wears her contacts with relative comfort for a week, it's just too easy to say, "What's the harm of another couple of days?" The secondary gains in cost savings and convenience put many patients on a slippery slope toward corneal disaster.

And these aren't just my patients. Industry data show that the number of contact lenses consumed per wearer each year has declined about 3% annually for a number of years. The reason? Patients are stretching out their wearing schedules.

Just ask your patients for their candid answer: How often do they really take out or change their contact lenses? Or, look over their lens purchase histories in your practice. If your patients are like mine, they're probably sleeping in hydrogel lenses longer than they should -- and certainly longer than you would like for the health of their eyes.

Unfortunately, it's not possible to guarantee that patients won't do this. But at least these new lenses will help to minimize the odds of damage if patients do wear their lenses longer than they should.

Convenience: It's hard to beat

With the safety of continuous-wear lenses established, I expect them to surge in popularity. Convenience drives the LASIK market, and I believe it will also drive the market for these new lenses.

Consider this: In the 1980s, before the adverse risks were fully understood, more than a third of all contact lens patients were wearing extended-wear lenses. Even more significant, those lenses doubled the contact lens population, from roughly 10 million in the United States at the start of the 1980s to 20 million by the start of the 1990s. Today's patients still want convenience, ease of use, and the pleasure of awakening with sight, so I believe there's a good chance that history will repeat itself.

In my practice, high-Dk/t silicone hydrogel lenses are proving themselves daily. To date, I've seen no infections and no corneal edema or pannus. At the same time, I've seen several migrating prescriptions stabilize. And our patients are ecstatic!

We now offer these lenses to all of our new and existing contact lens wearers.

Dr. Taub is Assistant Professor of Ophthalmology at Northwestern University in Chicago and medical director of the Taub Eye Centers.