silicone hydrogel contact lenses to your armamentarium against dropouts. Here's
Holden, PhD, DSc, FAAO (Dipl), and Desmond Fonn, MOptom
lenses really haven't made the grade yet. Some 2.5 billion spectacle wearers around
the globe still outnumber contact wearers by a 25-to-1 ratio. As many as 500 million
people need and can afford contact lenses, yet only 100 million wear them, according
to data compiled in 2003 by the International Association of Contact Lens Educators.
do these numbers mean in the United States? For starters, an estimated 2 to 3 million
people drop out contact lens wear each year, representing up to 10% of the wearing
marketplace.1 Of course, it doesn't have to be this way, especially with
new materials that can help resolve discomfort.
Why Silicone Hydrogels?
One way to attack
the problem is to fit silicone hydrogel contact lenses, the wave of the future.
As you know, these lenses have almost eliminated hypoxia for most contact lens wearers.
Now, we need to start thinking about comfort at insertion, end-of-day comfort and
Patients generally report that a high water-content daily disposable lens can initially
be more comfortable than a silicone hydrogel lens. But we've found this initial
comfort decreases over time, until the silicone hydrogel becomes as comfortable,
if not more comfortable, than a conventional hydrogel lens.
by Sickenberger2 showed that significant numbers of patients were more
comfortable in silicone hydrogel daily wear than conventional daily wear after 12
hours of daily wear. And Schafer3 published a study of 267 patients showing
that the percentage of patients who reported no discomfort after 6 months increased
the longer they wore silicone hydrogels, even when they wore them longer than 12
hours a day.
evaluating three silicone hydrogel lenses at the University of New South Wales in
Sydney, Australia, we found that their performance seemed to
improve over time, primarily because
wearers experienced decreased dryness compared with conventional lenses. Fonn's
data were even more dramatic, demonstrating that most patients preferred daily wear
PureVision over low-Dk hydrogel lenses in terms of comfort and less dryness over
the long term.
As we better
appreciate what success silicone hydrogels can deliver to practice, how should we
respond? It's comforting to know that we have many options in the daily wear and
extended wear categories. However, even a lens that fits well will challenge us
in terms of how well we can make it perform.
may see staining associated with two factors when managing patients wearing silicone
hydrogel contact lenses:
Edges and Pressure Zones. We're back in the fitting business with silicone hydrogels.
Conjunctival staining produced by the edges of these lenses can cause chronic late-day
discomfort. We're back in the fitting business with silicone hydrogels. Manufacturers
should pay attention to the edge shape of these stiffer lenses, and practitioners
should make sure they've selected the appropriate diameter and base curve.
Solutions. My colleagues and I just conducted a fairly substantial study of groups
of 40 patients with about six different lens care systems. We're definitely entering
an era when interactions between solutions and silicone hydrogel lens materials
can augment or interfere with comfort, and differently with some patients. But in
general, what we found is hydrogen peroxide solutions cause the least amount of
staining with silicone hydrogel contact lenses.
the University of New South Wales, our research studied average comfort levels for
Night & Day, Dailies, PureVision, Proclear and Acuvue 1-Day. All of these lenses
were grouped at an initial comfort rating of about 80 on a scale of 1 to 100. Although
80 might seem like a good number, it really is not. We need to achieve near 100
to attract and then keep patients in contact lenses. It isn't good enough for most
of the patients because with a standard deviation of 10, some are at 60 and only
some are at 100.
& Lomb surveyed more than 2,000 contact lens dropouts in 2001 and found they
weren't wearing their lenses anymore because:
� The lenses weren't comfortable enough.
Eyeglasses were more convenient.
Patients couldn't get accustomed to contact lenses.
Contact lenses didn't provide optimal vision.
The cost was too high. (I believe this is not a factor anymore, except in developing
was far and away the leading reason why these patients stopped wearing their lenses.
the End of the Day
With all the
lenses we've tried, no matter how good the material, we've found that comfort is
compromised by the end of the day, but less so with silicone hydrogels. When considering
all the design and material factors and the ways in which the contact lens
field will need to move forward we see that we don't have a strategy to go
to the next order of magnitude in comfort.
summary, we gathered data involving 536 patients over 5 years. We found 13.8% of
adverse-event-related discontinuations (2.6% per year) were associated with continuous
wear of silicone hydrogels. We also found a 6.5% average increase in giant papillary
conjunctivitis (1.5% per year).
other symptoms and signs, such as discomfort, seemed to decrease as reasons for
discontinuation. It appears that when patients are still successfully wearing silicone
hydrogel contact lenses after
2 to 8 weeks, they do very well in the long term.
Where Do We Go
Can we reduce
the adverse responses some patients experience? Perhaps communicating better with
patients about how to care for their eyes and their contact lenses will help. In
a recent study,4 we found too many of our patients swam without goggles,
smoked, wore their contact lenses in the shower without shutting their eyes, and
didn't always wash their hands before handling their lenses. We found a microbial
keratitis rate of about 1 in 200 with conventional extended wear and 1 in 1,000
with continuous wear hydrogels; the adverse response rate was about 1 in 50. Studies
of antibacterial lenses will begin next year and should help us with these issues.
course, we'll need to make progress on many other fronts besides the development
of lens materials.
Fonn reminds us, every contact lens destabilizes the tear film. The work of Glasson5
showed us that tear breakup time on contact lenses is between 5 and 9 seconds for
60% of these lenses, which is only one-third of the average breakup time for the
eye. Today, we have the best lenses ever well-designed, with high oxygen
transmissibility and good surfaces. What we need on top of that is a tear film that
behaves as though the surface on the lens is like the eye's own surface.
indicates that the fundamental comfort barrier is creating a lubricious, wettable,
long-lasting surface on the new generation of contact lenses. If solutions can enhance
that layer, it will really make an impact on the future comfort of contact lens
wear. We're getting there, slowly but surely.
is Scientia Professor of the University of New South Wales; founder and director
of the Cornea and Contact Lens Research Unit at the School of Optometry and Vision
Science, University of New South Wales; and deputy CEO of the Vision Cooperative
1. Fonn D. Preventing
contact lens dropouts. Contact Lens Spectrum. 2002;17:26-32.
Sickenberger W. Are silicone hydrogels suitable for dry eye conditions in a daily
wear modality? http://www.siliconehydrogels.com February 2004.
Schafer J. A characterization of dryness symptoms with silicone hydrogel contact
lenses. American Academy of Optometry,
http://www.aaopt.org/ December 2003.
Preliminary data, Australia and New Zealand Microbial Keratitis Study, 2004.
Glasson MJ, Stapleton F, Keay L, et al. Differences in clinical parameters and tear
film of tolerant and intolerant contact lens wearers. Invest Ophthalmol Vis Sci.
Contact Lens Spectrum, Issue: April 2005