contact
lens materials
Battling
the Misconceptions of Silicone Hydrogel Lenses
BY N. REX GHORMLEY, OD,
FAAO
I've participated in numerous silicone
hydrogel symposiums across the United States in the last year. At the events, we
asked participants, "Do you still fit PMMA lenses on your new contact lens patients?" The surprising result:
25 percent to 30 percent in several cities answered "yes." In addition, 50 percent
had fit fewer than 50 patients with silicone hydrogel contact lenses.
Currently, four spherical silicone
hydrogel contact lenses (Acuvue Advance [Vistakon], Night & Day and O2Optix
[CIBA Vision] and PureVision [Bausch & Lomb]) are available in the United
States. Later this year, Vistakon will introduce the Acuvue Oasys in the United
States. The major lens companies are currently doing almost all research with silicone
hydrogel technology. I believe the future of contact lenses is definitely with
these new materials.
So why are many practitioners slow
to adapt to them? Let me address some of the most common "excuses" for not fitting
silicone hydrogel lenses.
1. If it's Not Broken, Don't
Fix it
Chronic hypoxia can cause
corneal edema, neovascularization, ocular redness, endothelial polymegethism, changes
in corneal topography, myopic creep and reduced contact lens wearing time. It's our responsibility
to be proactive and prescribe the "best" lenses for our patients.
Primary care physicians
discuss the serious complications of smoking with all patients who smoke —
even when these patients don't yet have complications from smoking. Why should we
avoid treating our patients who similarly may develop serious complications from
wearing a low-Dk contact lens?
2. They're too Expensive
The most expensive silicone
hydrogel lens is less expensive than a toric or a bifocal soft contact lens. In
my practice, specialty lens patients don't complain about costs because they know
and appreciate the benefits of these lenses. If you educate your patients about
the many benefits of these lenses, then price isn't an issue.
3. They're Uncomfortable
When silicone hydrogel lenses
first entered the US market, only one base curve was available and the lens materials
had a "stiff" modulus. We now have several base curves, diameters and lens materials of differing
modulus available. With proper fitting, patients should find the lenses comfortable.
In addition, patients may experience a "rebound effect" resulting from an end to
chronic hypoxia, in which for a short time patients may have more sensitive corneas
because of the additional oxygen. Again, educate your patients that they may have
some adaptation to these new materials, and comfort won't be an issue.
4. Parameters are Limited
We now have silicone hydrogel
lens powers from +8.00D to –12.00D, several different diameters and base curves
and materials with different modulus. In addition, by this summer we'll have three
toric silicone hydrogel lenses. At least one manufacturer plans to release a bifocal
silicone hydrogel in the United States. So, are parameters a problem? No! By the
end of this decade, I predict that we'll have color silicone hydrogel lenses,
numerous bifocal lens designs and single-use silicone hydrogel lenses.
No More Excuses
When Canadians at a symposium
responded to that same question, no one answered "yes." Maybe
Canadians "get it" because they have had this technology longer.
I
do hope my US colleagues "wake up" and start using this new technology
soon!
Dr. Ghormley is
in private practice in St. Louis, MO. He is a past president of the American Academy
of Optometry and is a Diplomate of its Cornea & Contact Lens Section. He is
also a consultant to CIBA Vision.
Contact Lens Spectrum, Issue: June 2005