contact lens care
Caring
for Silicone Hydrogel Contact Lenses — Part 2
BY SUSAN J. GROMACKI,
OD, MS, FAAO
Click here to view
part 1 and
part 3.
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.
Contact Lens Spectrum, Issue: June 2005