contact lens materials

Introducing a Made-to-Order Silicone Hydrogel Lens
BY LYNDON JONES, PHD, FCOPTOM, FAAO, KATHY DUMBLETON, MSC, MCOPTOM, FAAO, & JILL WOODS, BSC, MCOPTOM

One disadvantage of most currently available silicone hydrogel lenses is that they're available only in a limited number of parameters. While these parameters are adequate for many patients, there are inevitably occasions in which practitioners can't fit patients who would ideally benefit from the oxygen performance of a silicone hydrogel.

A Custom Option

CIBA Vision has recently introduced O₂Optix Custom, a silicone hydrogel material in a made-to-order design. It's available in a wide range of base curves and diameters as well as an extensive power range (Table 1).

While initially limited to a single-vision spherical design, CIBA plans to over time make this lens material available in extended designs, including torics and bifocals. A made-to-order silicone hydrogel will greatly aid practitioners when fitting patients who have abnormally small or large, or flat or steep eyes and for patients whose prescription is outside the power range currently available.

Similarities and Differences

What remains unchanged between the new lens and other CIBA silicone hydrogel products is the biaspheric design, the plasma surface treatment (which produces a high-refractive-index, 25nm-thick plasma coating on the lens surface) and that the lens can be used with all available care products.

What is novel is the manufacturing process. Almost all spherical frequent replacement lenses made since the early 1990s have been molded. However, custom lenses need to be manufactured via a lathing process. This has been difficult to achieve because most silicone-containing polymers are too rubbery to lathe.

CIBA Vision overcame this problem by developing a latheable polymer called sifilcon A, with a water content of 32 percent and Dk of 82. CIBA manufactures the O₂Optix Custom lens via its patented InnoLathe process, which produces a rounded edge profile for better comfort.

O₂Optix Custom is initially available only for daily wear and quarterly replacement. CIBA plans to seek overnight approval in the future.

More to Come

Our next column will describe when and how to fit the lens and how it performs in challenging cases.

For references, please visit www.clspectrum.com/references.asp and click on document #135.

Dr. Jones is the associate director of the Centre for Contact Lens Research and a professor at the School of Optometry at the University of Waterloo, Ontario, Canada. Dr. Dumbleton is a senior clinical scientist at the Centre for Contact Lens Research. Jill Woods is a clinical scientist at the Centre for Contact Lens Research.