INTERACTIONS
Lens-Solution Interactions
The potential for corneal staining warrants
careful consideration and raises complex questions.
DR.
CORBIN: Several studies,
such as those by Jones,1 Garofalo2 and Andrasko,3
have examined lens-solution interactions. What are your thoughts on the interactions
between various solutions and lenses?
DR. LIEVENS:
Andrasko's work this year will be of significant importance. Some of the data on
marrying specific solutions with specific lenses are just staggering. In the near
future, I believe we'll have rules like, "If you're wearing this lens material,
then you need one of these solutions." We need to be very specific from now on.
DR. TOWNSEND:
When I look at these studies, I think the overwhelming piece of information is that
right now, the solutions containing POLYQUAD® have the highest degree
of biocompatibility with all lenses. Obviously, there are still some issues, but
it looks like the solutions with POLYQUAD® have a much lower rate
of bio-
incompatibility than any other general group of solutions at this time.
DR. CORBIN:
The data support what you're saying, but when new solutions are introduced, we need
to consider more than just the preservative. The cleaning ability and wettability
are critically important in the overall picture with different lens materials and
in the patient's wearing comfort.
DR.
TOWNSEND: We need to look
at all formulation properties of the solution. If you look at the formulations of
Aquify* compared to Equate*, the concentration of PHMB is identical. The staining
differences are influenced by other components in the formulation.
|
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■Acceptable staining (<10%)
■Marginal
staining (10%-20%)
■Unacceptable staining (>20%) |
LOOKING AT LENS PARAMETERS
DR. SINDT:
It's
interesting how different the silicone hydrogel lenses are from one another. The
electron micrographs of the surfaces emphasize this wide variability, specifically,
different amounts of exposed silicone on their surfaces. The various preservative
agents and wetting systems in a contact lens solution will react differently on
those lens surfaces, thus affecting the solution's performance.
DR. CORBIN:
Basically, we're acknowledging
the different silicone hydrogel surface treatments may cause different degrees of
staining.
If you look at the staining
profiles in some of these studies, they hit a peak typically at 2 to 4 hours. Let's
say you look at a patient after 2 hours and see a significant amount of corneal
staining, but no symptoms or compromised vision. You see that same patient again
at the end of the day, and the cornea looks significantly better. What does
that mean to you? And how would it affect your lens and solution prescriptions?
What are your concerns?
DR.
TOWNSEND: It mimics a
typical drug release curve. This definitely suggests the lens is acting as a depot
for antimicrobial agents. Products are formulated to kill microbes on the lens but
to be safe on ocular tissues. However, we may still see some chronic damaging effects
with certain products.
One study showed that if you
compare the original ReNu* to ReNu MultiPlus*, the amount of staining is twice as
high. In this study, it appears that the staining was proportional to the preservative
concentration.4
DR. LIEVENS:
Also, the Group 2 lenses have
been shown to have significantly more corneal staining with PHMB-preserved solutions.4–5
Lens materials used in conjunction with different solutions result in different
degrees of corneal staining. When you look at the staining grid (page 7) and how,
in clinical practice, we're allowing patients to buy anything they want, it's incomprehensible.
The amount of staining that can occur when some solutions are used with some lenses
is unacceptable. Both contact lens practitioners and patients need to better understand
the differences between lens solutions.
DEFINING "SIGNIFICANT"
CORNEAL STAINING
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Let's Discuss Labeling |
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DR. CORBIN: I see two different perspectives
in product labeling. One is what's important to the doctor, and the other is what's
important to the patient. Unfortunately, until now, most contact lens practitioners
have not taken an active role in prescribing contact lens products. Patients take
it upon themselves to read the labels and see what seems to attract them. You've
all said the product labeling is confusing. What issues do you see?
DR. SINDT: Regarding product labeling, manufacturers
have to substantiate label claims. For example, manufacturers need to provide data
to substantiate claims such as "reconditions the lens surface." What does it mean
to us, and does it change how we think about a product? It certainly affects how
we communicate to our patients on what solution they should use.
DR. TOWNSEND: It's difficult
for patients and contact lens practitioners to compare product ingredients. For
example, there are multiple names for PHMB, including Dymed* and Trischem*. They're
the same chemical, but that's not well known. People see different names and assume
the substance is unique to the disinfecting solution, when in fact, they're all
the same chemical structure and often the same concentration. What's more, I think
it might help us to put better documentation on the sides of the bottles, like,
"This is not a stand-alone product."
DR. SZCZOTKA-FLYNN:
There
are some advances, but we need a greater effort. I applaud Alcon and other companies
that have pursued specific labeling for silicone hydrogel contact lenses. That will
help practitioners select the right lens/solution combination. |
DR. CORBIN:
When
Bausch & Lomb took ReNu with MoistureLoc* off the worldwide market, company
spokesmen said they are confident the other ReNu* products are physically compatible
with all lens materials, including silicone hydrogel lenses.6 In light
of the corneal staining issues and concerns, what are your thoughts on that?
DR. SINDT:
We've seen multiple studies
that show ReNu MultiPlus* has a higher proportion of staining in PureVision* lens
wearers.
DR. CORBIN:
When asked if corneal staining
is a problem with ReNu MultiPlus* Solution, company spokesmen answered that in 10
years of clinical evaluations, there was "no problem or issue with corneal staining
in ReNu MultiPlus" and "no clinically significant difference between ReNu MultiPlus
and any other lens care solution." They went on to say, "Extensive clinical evaluations
have shown corneal response to ReNu MultiPlus is clinically acceptable and similar
to other lens care solutions, and over 10 years of field observations have shown
ReNu MultiPlus to be safe and effective."6
DR.
TOWNSEND: That's ignoring
the numerous studies from Jones and others showing that ReNu MultiPlus* causes
significant staining with silicone hydrogel lenses in addition to some hydrogel
lenses.
DR.
SINDT: Just to play devil's
advocate, what is considered significant? Is 5% significant? 10%? 20%? What level
do we reach before everyone says, "I agree. That's significant staining." At what
level can we all agree? That's left up to us. Do we have to get all the way up to
71% using Equate* (currently the same formulation as ReNu MultiPlus*) and PureVision*?
DR. LIEVENS:
It's a very convenient way to
answer a very complicated question. Statistical significance is one thing, but clinical
significance is something altogether different. The paper7 I published
earlier this year did not include contact lenses at all. Subjects self-dosed the
treatment eye with various multipurpose solutions. In discussions with B&L after
that paper was published, they asked, "Statistics are one thing, but do you think
this is clinically significant?" And my response was, "When patients' tear breakup
times were near normal, and then the mean tear breakup time in the treatment eye
was around 3 seconds at 4 weeks of dosing, that's clinically significant to me.
When I see patients in a dry-eye practice with a tear breakup time of 3 seconds,
that causes me to act."
DR.
TOWNSEND: We've all seen
a definite staining problem with ReNu MultiPlus in silicone hydrogels in our
practices, and we've heard Lyndon Jones speak and read his article in Optometry
& Vision Science. A lot of patients who use ReNu MultiPlus with silicone hydrogel
lenses have — I wouldn't say "clinically significant" — but I would say
a dramatic degree of staining.
LOOKING CLOSELY AT "COMPATIBILITY"
DR. LIEVENS:
What about the physical compatibility statement? What does that refer to?
DR. SINDT:
It doesn't affect the diameter, the base curve, the power, or any physical measurements
of the contact lens. In contrast, Acuvue Advance* lenses and SoloCare* were reported
to actually change the parameters of the lens using this combination.
DR. CORBIN:
When companies multipurpose solutions are approved for use with silicone hydrogel
lenses, they cite laboratory studies showing the solutions are "physically compatible
with all soft lenses, including the leading silicone hydrogel lenses."
DR.
SINDT: We need to think critically
about the word "compatible" with any solution. We might be thinking corneas, and
they might be thinking base curves. In this case, it's compatible inasmuch as it
doesn't change the physical lens parameters.
DR.
CORBIN: I agree with you.
If the question were corneal compatibility, the answer would have to change. And
although we may not have a definition for what's clinically significant in terms
of corneal staining, there's certainly enough concern in the contact lens world
to make us examine these issues very closely. Until we have the answers, we certainly
want to reduce our patients' risk to the lowest level possible.
*Trademarks are the property of their respective owners.
REFERENCES
1. Jones L, MacDougall N, Sorbara LG. Asymptomatic
corneal staining associated with the use of balafilcon silicone-hydrogel contact
lenses disinfected with a polyaminopropyl biguanide-preserved care regimen. Optom
& Vis Sci. 2002. 79;12:753-761.
2. Garofalo RJ, Dassanayake N, Carey C, et al. Corneal staining
and subjective symptoms with multipurpose solutions as a function of time. Eye
& Contact Lens. 2005;31:166-174.
3. Andrasko GJ, Ryen KA, Garofalo RJ, Lemp JM. Compatibility of
Silicone Hydrogel Lenses With Multi-Purpose Solutions. Poster presented at ARVO
2006,
Ft. Lauderdale, Fla.
4. Young G, Pritchard N, Hunt C, Coleman S. Evaluation of Corneal
Staining Related to Multipurpose Disinfecting Systems, Poster presented at BCLA
2001.
5. Stiegemeier MJ, Cedrone R, Evans D, et al. Clinical Performance
of 'no rub' Multi-Purpose Solutions. Contact Lens Ant Eye. 2004:27:65-74.
6. Bausch & Lomb field document: ECP Questions &
Answers — Removal of MoistureLoc Worldwide.
7. Lievens CW, Hakim N, Chinn A. The effect of multipurpose
solutions on the ocular surface. Eye & Contact Lens. 2006;32:8-11.
Contact Lens Spectrum, Issue: August 2006