Silicone hydrogels: a new day for 30-day continuous wear

Over the years, practitioners have been reticent to endorse 30-day extended-wear contact lenses, largely due to repeated failures in implementing this modality. This skepticism, prompted by the high complication rate of the so-called “first-generation” extended-wear lenses, continues to taint the outlook of many optometrists regarding modern continuous-wear lenses.

“A lot of practitioners were burned by this in the past,” said Jennifer L. Smythe, OD, MS, FAAO, an associate professor of optometry and coordinator of the Cornea and Contact Lens residency at Pacific University College of Optometry. “So now they are going to tread cautiously, and that is a very pragmatic approach. I think there is a lot of hesitation.”

Although this hesitation is founded on valid concerns, practitioners are now urged to be open-minded regarding the potential of today’s silicone hydrogel contact lenses.

“I would encourage colleagues not to be shy in prescribing this modality,” said Joseph P. Shovlin, OD, FAAO, of the Northeastern Eye Institute, Scranton, Pa. “They are a completely different material — a hybrid material. We are talking about a significant increase in the amount of oxygen.”

Earlier versions: ultimately disappointing

The first extended-wear lenses were introduced in the late 1970s, according to Lyndon W. Jones, PhD, FCOptom, FAAO, associate director of the Centre for Contact Lens Research at the University of Waterloo.

These high-water content lenses were worn by patients for up to 3 months, Dr. Jones said. By around 1984, it became apparent that the lenses were causing complications, such as microbial keratitis. A study by the Contact Lens Institute was conducted in 1986, Dr. Jones said, and by 1989, the Food and Drug Administration reduced the accepted duration of wear to 7 days.

“And so we knew that the first generation of extended-wear lenses basically produced higher levels of microbial keratitis than if the same lenses were worn on a daily-wear basis,” Dr. Jones said.

The conclusion drawn from this information was that the lenses were accumulating Pseudomonas from patient handling. This Pseudomonas was thought to have been causing the microbial keratitis, Dr. Jones said.

This generated the idea of disposable extended-wear lenses, which were worn for 7 days and then replaced, Dr. Jones said. For a second time, extended-wear lenses were touted as safe. By the early 1990s, however, it became apparent that disposable lenses were not working either.

“The number of patients developing microbial keratitis while sleeping in a disposable extended-wear lens was still too high,” Dr. Jones said. “So, unfortunately, the contact lens industry was wrong again.”

Today’s silicone hydrogels

The issue of oxygen permeability is crucial when it comes to extended-wear contact lenses. It has been known for some time how much oxygen is needed to stop corneal swelling overnight, Dr. Jones said.

“When you close your eyes at night, you starve your cornea of oxygen, and your cornea swells by about 4% or 5%,” he said. “So, on top of the 4% that you get from just closing your eye, we add another 6% to that from wearing a conventional contact lens.”

Silicone hydrogel lenses transmit five to six times more oxygen than conventional lenses, Dr. Jones said, resulting in no extra corneal swelling. “You still get the 4% that you get from simply closing your eye,” he said, “but no additional swelling. So if you put a conventional lens on one eye, and a silicone hydrogel on the other, in the morning, you would have 10% swelling in one eye and 4% swelling in the other.”

Dr. Jones cited work by H. Dwight Cavanagh, MD, in Texas that suggests that the increased incidence of microbial keratitis with extended-wear contact lenses is related to a lack of oxygen. “If you compromise the cornea by cutting back the amount of oxygen, something happens to the surface of your corneal epithelium that makes bugs bind to it,” Dr. Jones said. “ If you swell the cornea in any way at all, the epithelium binds more bugs. So if you induce no extra swelling, then the bugs that are floating around in your eye can’t bind to the eye.”

Dr. Jones said because silicone hydrogel lenses supply more oxygen and reduce corneal swelling, there is a significantly lower incidence of microbial keratitis. “We will still see microbial keratitis with patients who wear silicone hydrogel lenses. To date, 14 cases have been recorded worldwide,” he said. “But there is no question that, at this moment in time, the numbers indicate that if you sleep in a silicone hydrogel lens for 30 nights, your chance of developing microbial keratitis is no greater than with regular daily wear.”

Prescribing extended wear

The question of how to prescribe continuous-wear silicone hydrogel lenses is not one that is dealt with uniformly among practitioners. For many, this issue is addressed on a case-by-case basis.

“We allow them and their eyes to decide how long they can wear it,” said Peter Donshik, MD, a contact lens specialist and published author located in Bloomfield, Conn. “We usually follow them during the first month at 1 day, 1 week and 3 to 4 weeks. Then, we can usually tell whether they are able to wear it for the full 30 days or close to 30 days.”

Dr. Donshik said about 75% of his extended-wear patients are able to wear the lenses for between 21 and 30 days. He said he also sometimes prescribes the lenses for daily wear, “especially in those patients who have problems with dry eye, who show evidence of epithelial edema with regular lenses or who want to wear them on a flexible schedule,” he said. “We give them that option.”

Dr. Smythe said she has addressed the topic of extended wear with groups of practitioners during interactive meetings and usually finds that about half of the optometrists polled prescribe the lenses for a full 30 days.

“I usually do a head count, and it’s about 50/50,” she said. “Some practitioners are hesitant to jump right in with the idea of continuous wear.”

Of those practitioners who are currently fitting the lenses, Dr. Smythe said a portion of them started out prescribing them as daily wear and, once comfortable, went on to prescribe them as extended wear. “Once they see that this is very different from the old extended wear, they are more comfortable recommending it to patients,” she said.

According to Dr. Shovlin, extended wear is not for every patient, and so he assesses each case carefully. “Depending on how we view their status when they come in for a progress check, we will go anywhere from daily wear up to 30 days, with a good number of patients removing them on a weekly basis,” he said. “Some patients will remove them after 15 days, and a fair number of patients do make it for the full 30 days, assuming that all is going well.”

Dr. Shovlin added that, unlike extended-wear lenses of the past, silicone hydrogel lenses are probably not “dose-related” in terms of complications.

“In the past, if you were an extended-wear patient with the first generation, with the HEMA materials, there was a significant increase in corneal morbidity if you wore those lenses beyond 7 days,” he said. “That is why the FDA rolled back the number of days from 30 to 7, because it was shown that the increased risk of infection was dose-related beyond 7 days.”

With the current silicone hydrogel lenses, no data indicate any sort of dose-related problems. “That hasn’t been proven with these lenses. In fact, it is the opposite,” Dr. Shovlin said. “The FDA is giving the practitioner and the patient reasonable assurance of safety and efficacy. And there is a clinical post-market surveillance showing impressive results for 30-day wear.”

Getting started

Dr. Smythe recommended that, when beginning to prescribe continuous-wear lenses, practitioners should put together their own small “study” for observation purposes.

“I suggest trying to get 10 patients in the lenses as continuous wear, and use that as a mini-clinical study of your own,” she said. “That is how you gain the confidence — by seeing the patients, how much healthier their eyes are and how happy they are.”

The future of extended wear

Dr. Donshik believes that continuous-wear silicone hydrogel lenses are emerging as a viable alternative to LASIK and other refractive surgeries.

“It is an alternative form of vision correction,” he said. “Anybody who is thinking about undergoing LASIK should be told about this as an option, because for most patients who have the appropriate refractive error, this gives you everything LASIK does without the surgery.”

Dr. Jones said a few obstacles need to be worked out if extended-wear lenses are to reach their full potential. “One is the cost,” he said. “We need to drive the cost down. These are brand-new, very complicated lenses. Once we can get the manufacturing worked out, that will drop the cost.”

In addition, Dr. Jones pointed out that supply and demand will also drop the cost of the lenses. “That will help grow the market enormously,” he said.

The fact that the lenses are surface-treated is another aspect that should be improved, according to Dr. Jones. “For the first time ever, we have a lens with a very different bulk chemistry from its surface chemistry, so these lenses need to be surface-treated,” he said. “The surface treatments need to be improved, ideally to the point where we can get a tear break-up time over the lenses that is about the same time as the tear break-up over the cornea. When we do that, this will literally change contact lenses forever.”

For Your Information:

• Jennifer L. Smythe, OD, MS, FAAO, writes a regular column for Primary Care Optometry News on the subject of contact lenses and is an Editorial Board member. She is an associate professor of optometry and coordinator of the Cornea and Contact Lens residency at Pacific University College of Optometry. Dr. Smythe also sees patients in private group practice at Murrayhill Eyecare in Beaverton, Ore. She can be reached at Pacific University College of Optometry, 2043 College Way, Forest Grove, OR 97116; (503) 359-2770; fax: (503) 359-2929; e-mail: smythej@pacificu.edu. Dr. Smythe has no direct financial interest in the products mentioned in this article, nor is she a paid consultant for any companies mentioned.
• Joseph P. Shovlin, OD, FAAO, is a Primary Care Optometry News Editorial Board member and practitioner at the Northeastern Eye Institute. He can be reached at 200 Mifflin Ave., Scranton, PA 18503; (570) 342-3145; fax: (570) 344-1309; e-mail: jshovlin@aol.com. Dr. Shovlin has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
• Peter Donshik, MD, is a contact lens specialist located in Bloomfield, Conn. He can be reached at 47 Jolley Dr., Bloomfield, CT 06002; (860) 286-5448; fax: (860) 286-5449. Dr. Donshik has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned, but he has received research funds from CIBA.
• Lyndon W. Jones, PhD, FCOptom, FAAO, is the associate director of the Centre for Contact Lens Research (CCLR) at the University of Waterloo in Ontario, Canada. He can be reached at the CCLR, School of Optometry, University of Waterloo, Waterloo, ON N2l 3G1 Canada; (519) 888-4567; fax: (519) 884-8769. Dr. Jones has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned. Some of the research conducted at the CCLR is sponsored by manufacturers of silicone hydrogels.