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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.
Contact Lens Spectrum, Issue: February 2007