Silicone hydrogel allows toric contact lens' long-term wear

May 15, 2005

In a 24/7 world, the availability of the PureVision Toric Contact Lens (Bausch & Lomb) that incorporates an aspheric design is welcome news. The FDA approval in early April of the silicone hydrogel contact lens will offer patients who wear their lenses for long periods—even overnight—a healthy and more comfortable alternative to traditional hydroxyethylmethacrylate (HEMA) contact lenses.

The high oxygen permeability of balafilcon A, the company's silicone hydrogel material, allows 300% to 500% more oxygen transmission than traditional HEMA lenses, according to Dennis Ruskin, OD, FAAO, an optometrist with the Finch Midland Optometric Clinic in Toronto.

"Patients who work in an office setting could be wearing their lenses for 18 to 19 hours a day, particularly in the fast merry-go-round of activity between work and pleasure," Dr. Ruskin said. "This lens is well-suited for patients who wish to maximize their wearing schedule without affecting their eyes."

The PureVision Toric lens is indicated for the correction of refractive ametropia with astigmatism of up to 5 D. The lens is designed for monthly replacement, and approved for either daily wear or up to 30-day continuous wear.

"We bombard the lens with electrically charged gas molecules, and that changes the matrix of the material," said Bausch & Lomb's Lisa Fawcett, director of contact lens marketing, United States.

She compared the special surface treatment with bread crust. Fawcett explained that it will not flake off, unlike the analogy of car paint flaking from metal-where it is truly just on the surface. The PureVision Performa surface is embedded in the lens.

The material also has a high percentage of bound water so it does not dehydrate as quickly, Fawcett added.

Physicians who are accustomed to the SofLens66 Toric will be comfortable shifting to the PureVision Toric lens because they are familiar with the design, Dr. Ruskin said. While Johnson & Johnson also launched a silicone hydrogel toric lens (AcuVue Advance for Astigmatism) in March, Dr. Ruskin said he has little experience with it.

"SofLens66 Toric is an excellent lens for comfort and visual acuity, so they (Bausch & Lomb) took the design of that lens and moved it into a new-generation contact lens material so that patients who have a more demanding lifestyle can be a little happier and they can have fewer complications," he said.

Dr. Ruskin called the use of silicone hydrogel "a very significant move forward." Although patients are instructed not to wear their contact lenses around the clock, many do not comply, he said.

"The new lens offers a safety net because the material has a much higher breathability, and its potential for complications from infection or an inability to get the minimum amount of oxygen is far, far less than a conventional lens," Dr. Ruskin said.

Another attractive feature of the lens is its prism ballast design, which prevents the lens from rotating and helps it to stabilize quickly in the eye, reducing chair time. Eye-care practitioners no longer have to wait 20 to 30 minutes for a lens to "settle in" to determine the actual prescription necessary, Dr. Ruskin said.

"It removes a lot of the guesswork, because you can take the spherocylindrical record and convert that to a contact lens, and that is the first lens-and in many cases, that is the final lens," he explained.

Finally, the lens' aspheric design removes visual distortion in low-light situations when pupil sizes are larger; it "fine-tunes" visual quality, Fawcett said.