contact lens care
Caring for Silicone Hydrogel Contact Lenses Part 2
In 1979, the FDA devised a classification system (Groups I, II, III and IV) to aid practitioners in contact lens-solution interaction and care. Interestingly, the four silicone hydrogel contact lens materials fall into two different groups. Most of us agree that they're more alike than not. However, questions remain, such as, "Do they deserve their own, new classification group, or are they dissimilar enough to form three or four new groups?"
Available Silicone Hydrogels
PureVision (balafilcon A, Bausch & Lomb) was the first silicone hydrogel contact lens introduced in the United States (1999). It was temporarily unavailable because of a patent infringement lawsuit by CIBA Vision, but made its return on April 27, 2005 for up to 30 days of continuous wear.
PureVision has a 110 Dk/t for a –3.00D lens and 36 percent water content, placing it in the FDA Group III (low water, ionic). To render the lens surface hydrophilic, PureVision contact lenses undergo plasma treatment that results in a wettable surface that can't be stripped away, which transforms the silicone components on the surface into silicate compounds. These glassy "islands" bridge over the hydrophobic underlying material, forming a permanent part of the lens.
Night & Day (lotrafilcon A, CIBA Vision) also has approval for 30 days of continuous wear. It has a 175 Dk/t and a water content of 24 percent, positioning it in Group I (low water, nonionic). To add hydrophilicity, Night & Day's lens surface undergoes incorporation of plasma, which can't be stripped away from the base material.
O2Optix (lotrafilcon B, CIBA Vision) is a two-week disposable lens approved for up to six nights of extended wear. It's also a Group I lens with a 137 Dk/t and water content of 33 percent. This lens's plasma surface treatment is similar to that of Night & Day's.
Acuvue Advance (galyfilcon A, Vistakon), another silicone hydrogel member of Group I, is a two-week disposable lens with an 86 Dk/t and 47 percent water content. The only silicone hydrogel on the market with UV blocking, its hydrophilicity is provided by Hydraclear, an internal wetting agent.
Go With What You Know
These materials are so new that we aren't yet aware of all solution-material-eye interactions. For the FDA to approve a contact lens, it need be tested with only one multipurpose solution (of the lens manufacturer's choosing). A solution must be tested with one Group I and one Group IV lens for approval. As written above, even within Group I, silicone hydrogels vary greatly in composition and properties from hydrogels and from each other.
As a result, it's important to consider that only these solutions have specific approval for use with silicone hydrogel lenses: Opti-Free Express (Alcon), Clear Care (CIBA) and Aquify 5 Minute Multi-Purpose Solution (CIBA). It's imperative in all situations, but especially in this one, to specifically instruct patients to make no substitutions. We don't know enough yet about all potential interactions. What we do know, I'll discuss in my next column.
Dr. Gromacki is in group practice in Burke, Virginia, and has served as a faculty member at the University of Michigan Department of Ophthalmology and Visual Sciences.