Silicone Hydrogels -- Are They Really That Different?
BY JOSEPH T. BARR, OD, MS, FAAO, EDITOR
Rarely do I talk in my editorial about topics that appear in the same issue. I usually consider that readers want more -- not just a rehash of what we're running this month. Neal Bailey, OD, PhD, taught me this principle years ago, and I've tried to remain true to it.
For this month, Loretta Szczotka-Flynn, OD, MS, FAAO, has written a column about a proposed new contact lens classification. She discusses and converses with Ralph Stone, PhD, the author of the "FDA's" four lens groups in that he used four lens properties (low and high water, ionic and nonionic) to create the current FDA contact lens classification system:
- Group 1 -- low water, nonionic
- Group 2 -- high water, nonionic
- Group 3 -- low water, ionic
- Group 4 -- high water, ionic
I have for the past few years agreed with these groupings. But now I'm not sure. Clearly, silicone hydrogel lenses don't act similarly. They don't react the same with lens care solutions. They may or may not have surface treatments. They may have either high or low water content. Others will inevitably arise. As Dr. Szczotka-Flynn says, you need to know that they react differently to different situations.
Maybe Dr. Stone had it right in the beginning. Even though the lens chemistry situation gets more and more complicated and even though the current system isn't perfect, we need more time to make sure we get the next classification right.
Contact Lens Spectrum, Issue: February 2005