Optimizing GP Wettability and Performance
BY EDWARD S. BENNETT, OD, MSED
The GP industry is a dynamic one that benefits from the ongoing introduction of new materials. From the days of PMMA corneal design lenses in the 1950s through 1970s to the siliconeacrylate lens materials of the 1980s to the fluorosiliconeacrylate (FSA) materials from the mid-1980s to the present, GP materials have continued to evolve.
Two companies that have recently introduced FSA materials purported to have optimum surface wettability are Contamac US, Inc. with its Optimum lens family and Lagado Corporation with its Onsi-56 and Tyro-97.
Optimum Lens Family
The Optimum family of materials includes Optimum Classic (Dk = 26), Optimum Comfort (Dk = 65), Optimum Extra (Dk = 100) and Optimum Extreme (Dk = 125). Optimum Classic is the mainstream lens that offers optimum stability and lends itself to producing unusual lens geometries as well as very thin designs. Contamac polymerizes its lens materials via a proprietary new technology process that claims to not induce stress into the finished product. These are modified FSA materials that incorporate HEMA to optimize surface wettability. One study (Knutson et al) that appeared in the May 2005 issue reported on refitting 103 GP wearers into these materials. At minimum, four out of five patients preferred the Optimum material to their previous one; one-third indicated that the new lenses were much better than their old ones, and only five participants wanted to return to their old lenses. Contamac recommends Optimum, by Lobob, GP solutions for these materials.
Onsi-56 and Tyro-97
The Lagado Corporation has introduced Onsi-56 and, most recently, Tyro-97. These lenses also contain HEMA and are modified FSA lens materials. Although Lagado has used the term "rigid silicone hydrogel" in promoting them, it's important to note that the FDA hasn't established any such category.
These materials achieve their surface wettability via a combination of HEMA and a high proportion of fluoromonomer within the polymer formulation. Water is attracted to the lens surface but not absorbed into the interior of the lens. These materials have no temporary surface modification or treatment and are also available in toric and bifocal designs. Lagado recommends Onsi-56 (Dk = 56) for all standard cases (daily wear myopes) and Tyro-97 (Dk = 97) for wearers who need higher oxygen permeability and thicker lens designs.
Eef van der Worp (2005) reported on 29 patients who were refit into Onsi-56 (termed Comfort O2 in the Netherlands); 96 percent of these patients reported similar or better comfort with their new lenses. For the entire patient sample, researchers found a statistically significant increase of 15.7 percent in comfort. Optimum Solutions are recommended for these materials as well.
See for Yourself
It's important to downplay the promotional efforts as they pertain to low wetting angles with these materials. Your best approach is twofold: First, try these materials on patients who exhibit dryness and deposit-related problems with their current GP and soft lenses. Second, obtain feedback from colleagues you trust who have experience with any of these new materials.
It's evident that advances in material polymer chemistry are occurring today, and I compliment Contamac US and Lagado Corporation for continuing to push the envelope in GP material performance.
For references, please visit www.clspectrum.com/references.asp and click on document #123.
Dr. Bennett is an associate professor of optometry at the University of Missouri-St. Louis and is executive director of the GP Lens Institute.