discovering
dry eye
Dry Eye
News From the BCLA
BY
JASON J. NICHOLS, OD, MPH, PHD
For those of you unfamiliar with the British
Contact Lens Association (BCLA), it's an organization that strives to promote the
clinical practice and science of contact lenses. At this year's meeting,
there were more than 1,200 participants from more than 40 countries. Following are
some highlights of significant research or events related to the tear film, dry
eye and contact lenses from this year's meeting.
Studying Tear Mixing
Dr. Ken Polse gave the BCLA Medal address, presenting an account
of his research that originally centered on corneal hypoxia related to lens wear
and has more recently focused on "tear mixing." The main goal of the tear mixing
lab at the University of California is to understand factors that control tear mixing
under a contact lens, such as post-lens tear film thickness, lateral and transverse
lens motion, material modulus and overall diameter. The lab has also focused on
the impact of lens fenestrations relative to improving tear exchange.
Silicone Hydrogel News
Vistakon announced the launch of its Acuvue Oasys (senofilcon
A) and 1-Day Acuvue Moist contact lenses. Oasys is a new silicone hydrogel lens
that Vistakon is targeting for the contact lens-related dry eye population. It has
a Dk/t of 147 and doesn't have a surface treatment, but rather incorporates polyvinyl
pyrolidone (PVP), which may improve wettability. The 1-Day Acuvue Moist is a daily
disposable lens that is similarly targeted for the contact lens-related dry eye
population.
Coopervision announced the development of its new silicone hydrogel
material, comfilcon A. While maintaining a significant Dk/t, the material is "naturally
wettable" and doesn't have a surface treatment or wetting agents. Further, the material
has a lower modulus and higher water content than other available silicone hydrogel
materials, which may improve wearing comfort.
Drs. Brian Tighe and Lyndon Jones independently presented scientific
research on biocompatibility and wettability of silicone hydrogels. Dr. Tighe's
group reported that the new Acuvue PVP-associated materials had lower advancing
contact angles when fully hydrated and low coefficients of friction in comparison
with the other silicone hydrogels, and that CIBA Vision's Focus Dailies (nelfilcon
A) can release polyvinyl alcohol (PVA), which should, in theory, improve lens and
tear film interaction.
Dr. Jones's group, based at the University of Waterloo, showed
that traditional hydrogel lenses were associated with good initial comfort, but
end-of-day discomfort corresponding to decreased wettability. Silicone hydrogel
contact angles were initially high, but decreased over the day's wear; various multipurpose
solutions as well as protein and lipid deposits can also significantly impact these
contact angles.
Surfactant Action
Research from Alcon Laboratories showed that the use of surfactants
(particularly tetronic 1304) in multipurpose solutions has a significant impact
on hydrogel lens wettability. Surfactants work by reducing the surface tension of
a film, allowing for an even and uniform spread of the tear film over a lens.
Strides in Tear Film Analysis
Drs. Kelly Nichols and Franz Grus independently presented new
mass spectrometry-based analytical methods for analyzing tear film lipids and proteins,
respectively. These methods have significant promise in targeting biomarkers associated
with dry eye disease in general, or potentially for the contact lens wearer. Manufacturers
may then target these biomarkers relative to specific pharmaceuticals or lens care
cleaning products.
A Clear Goal in Mind
As this and other scientific work translates into patient care,
it's clear that the contact lens field as a whole is aimed at targeting contact
lens-related dry eye.
Dr. Nichols is assistant
professor of optometry and vision science at The Ohio State University College of
Optometry.
Contact Lens Spectrum, Issue: September 2005