contact lens materials
Introducing the Latest
lens has joined the ranks in the silicone hydrogel market. The Acuvue Oasys (Vistakon)
now adds to a class of lens materials that many believe will replace traditional
hydrogel products in
the not-so-distant future.
Acuvue Oasys is made of senofilcon
A, a 38 percent water content lens that has more silicone, less water and more Hydraclear
than Vistakon's Acuvue Advance galyfilcon A material. Hydraclear is an internal
wetting agent that eliminates the need for a surface treatment, as other lenses
in this class require. The company claims that the Hydraclear material is more compressed
in the senofilcon A product, creating a smoother, wettable surface that approaches
the smoothness and wetness of the cornea.
The Dk value of Acuvue Oasys is
103, which provides a Dk/t value of 147 at a center thickness of 0.07mm for minus
powers. Currently, the FDA has cleared Vistakon's 510(k) application for daily wear of senofilcon
Comparing Apples to
Table 1 shows how the available
silicone hydrogel lenses stack up to one another. Remember that industry reported
Dk/t values simply provide the transmissibility through the thinnest portion of
a –3.00D lens. The Dk/t will vary across any lens, with significantly diminished
values in the periphery of a high-minus lens or in the center
of a plus lens. Note that manufacturers have expanded many of the silicone hydrogel
parameters since their initial launch, with available sphere powers now from +8.00D
Silicone Hydrogel Advantages
Compared to traditional
hydrogels, silicone hydrogel materials have lower water contents, higher bound water
and greater oxygen transmissibility, providing more than 95 percent oxygen availability
to the cornea in the open eye state, according to Brennan.
Not only are silicone hydrogels the lenses
of choice for overnight use, but they may soon be positioned for patients who suffer
from situational dryness and exposure to constant or occasional adverse environments.
These include computer use (because of low blink rate and larger palpebral aperture),
TABLE 1 - Currently
Available Silicone Hydrogel Lenses
||+6.00 to –10.00
||+6.00 to –12.00
||+8.00 to –12.00
is an associate professor at Case Western Reserve University Dept. of Ophthalmology
and is director of the Contact Lens Service at University Hospitals of Cleveland.
Contact Lens Spectrum, Issue: August 2005