Disinfection
Disinfection Criteria For Multipurpose Contact
Lens Solutions
Panelists
discuss the importance of real-world testing
GLENN S. CORBIN, OD:
Let's discuss how we evaluate
the disinfection characteristics of contact lens solutions.
CHRISTINE W. SINDT,
OD, FAAO: In my opinion, no patient
understands the difference between a multipurpose disinfecting solution (MPDS) and
a multipurpose solution (MPS). In fact, practitioners often consider these products
equivalent as well. The criteria for a contact lens solution to be labeled a MPDS
are more stringent than those for the labeling of a MPS. In order to be a MPDS,
the product must meet the primary criteria of the stand-alone test, which requires
a higher level of efficacy.
STAND-ALONE TESTING
AND CONTACT LENS UPTAKE
LORETTA SZCZOTKA-FLYNN,
OD, MS, FAAO: Stand-alone testing
does not require a lens; however, regimen testing does. Preservatives can be taken
up by the lens either within the matrix or onto the lens surface. The question is:
Is preservative uptake by the lens a beneficial or detrimental effect of this interaction.
For example, one might suppose having preservatives present at the lens surface
where microbes can attach would decrease the risk of infection if the preservative
was gentle to the cornea.
DR. CORBIN:
A study1 looked at how different solutions disinfect in the presence
of a contact lens. There were big differences in the products' efficacy against
Pseudomonas and Staphylococcus aureus. When we look at the findings with and without
lenses, they are different. Yet doctors and patients don't know the difference.
WILLIAM
D. TOWNSEND, OD: Three
of the products were preserved with the same preservative, PHMB (a biguanide preservative),
yet there were differences in results for Pseudomonas and Staph. This suggests the
formulation has some impact on antimicrobial efficacy.
DR. CORBIN:
The data show that according
to the amount of antimicrobial activity of the solution remaining in the case after
the lens was soaked in ReNu MultiPlus* solution, the lens absorbed much of the solution's
disinfectant. There's very little left.
DR. SINDT:
Some of the preservative agents
can bind to the surface of the contact lens and be taken up into it. If you look
at Alcon's published antimicrobial data,2 they tested "real-world conditions"
by including a contact lens. These types of studies help us to understand how the
solution will work with our patients.
DR.
SZCZOTKA-FLYNN: Another
issue that's come to light is lens groupings. With silicone hydrogel lenses coming
to the forefront, they should probably have their own lens group because they may
behave very differently than low-Dk products in the presence of solutions.
DIFFERENTIATING SOLUTIONS:
DR. CORBIN:
Awareness
is an issue as well. Most of our colleagues think, "juice is juice" when it comes
to contact lens solutions. They don't understand there are differences, and it took
the unfortunate recent rise in fungal keratitis to bring solution differences to
light. We need to understand the science of the product. Not only do we need to
look at the preservative agents themselves — biguanides vs. non-biguanides,
for example — but we have to examine the impact of the final formulation on
lens-solution interactions. Solutions with the same biguanide preservative can differ
in the preservative's uptake and release profiles based on their product formulations,
so there are many factors to consider.
DR. TOWNSEND:
At my recent lectures, a lot of practitioners have said to me, "I had no idea about
the differences in lens-care products." We owe it to our patients and our profession
to make a concentrated effort to educate each other in the subtle and not-so-subtle
differences between solutions. We all need to know the different kinds of lens solutions
and the disinfecting abilities of different types of preservatives.
DR. SINDT:
Practitioners think, "It's a
preservative," and they think about it in terms of killing micro-organisms on a
lens. They don't think about the preservative's impact on other cells, such as corneal
cells.
DR. TOWNSEND:
I have noticed increased attendance
at my contact lens solutions lectures in the last couple of months. These numbers
point to a turnaround in practitioner interest in solution-related contact lens
interactions. The recent keratitis problem has pointed out to all of us a need to
study and learn more about this topic.
DR. CORBIN:
This is a landmark for eyecare professionals because this is really the first time
a medical issue of this nature is in the national headlines.
DR.
TOWNSEND: Absolutely.
And how we handle this is important. We've been explaining to people that contact
lens wear is still a safe modality.
DR. CORBIN:
Eyecare professionals must learn
more, and we need to improve how we pass this information along to patients to promote
compliance and support good decisions for ocular health.
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"NORMAL" CORNEAL STAINING? |
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Corneal staining is common and often asymptomatic.
What are we willing to live with?
DR. CORBIN: One
of my questions is always, what are we willing to live with as far as corneal staining?
It's inevitable that most contact lens patients will have some stippling when they
remove their lenses after a day of wear, whether it's one or a half-dozen areas
of micro punctate staining. Random stippling is not an issue, and I don't think
you can avoid it in anyone but the rare patient. But when we check a patient after
2 hours of wear and see significant staining, usually without symptoms, we have
concerns. There may be an increased avenue for infection, and there's the potential
for corneal edema and cytokine release.
DR. SZCZOTKA-FLYNN:
Two posters at the 2006 annual meeting of the Association for Research in Vision
and Ophthalmology (ARVO) explored potential risk factors for corneal infiltrative
events
and the relationship between corneal staining and the development of
infiltrates.1,2 Jalbert and colleagues studied daily wear patients, and
our group explored risk factors in an extended wear group
of patients. The published
reports of these abstracts are pending.
CHRISTOPHER W. LIEVENS,
OD: The take-home message, even without the keratitis issue, is that we have to
stain patients. For how many years have most practitioners had soft contact lens
patients and not stained them at all? Without the introduction of silicone hydrogels,
we might have continued for years without recognizing the need to stain. We need
to measure corneal staining.
ASYMPTOMATIC PATIENTS
DR. CORBIN: If
we look at the long-term effects of staining, without considering one particular
product or lens design, do you think it's linked to the 10% patient dropout
rate3 in soft contact lens wearers?
DR. SZCZOTKA-FLYNN:
The studies would argue against that because they show that, in most cases, the
staining seems to be asymptomatic. Staining is not even correlated to limbal redness.
DR. LIEVENS: If preservatives
get onto the surface of the lens or even into the matrix and then get released to
the ocular surface, I wonder what chronic problems may occur. I don't think anyone
has determined exactly what causes asymptomatic corneal staining. We commonly see
an annulus of staining in the peripheral cornea that spares the central cornea.
It's such an unusual pattern, and it's not necessarily consistent with solution
toxicity. My worry is that certain solutions may be part of the cause of the corneal
staining and epithelial cell compromise.
AN OPENING FOR COMPLICATIONS?
DR. SINDT: Absent
symptoms, what's the significance of corneal staining? Obviously, I've been thinking
a lot these days about infections and fungus. I used to see fungus on contact lenses
all the time. People who kept their lenses too long had fungus all over them and
never developed keratitis. Why are patients having problems now? Could it be the
staining issue? Is the staining giving the micro-organisms the inroad they need?
Our bodies are pretty good at fighting off pathogens, but is corneal staining giving
them a nidus for potential problems?
DR. SZCZOTKA-FLYNN: Polse and Lin and colleagues have used fluorophotometry to look at the epithelial
barrier function. If we look at that more intensely, we might get our answer. If
the tight junctions of the cornea are getting leaky and organisms can penetrate
easier, then that could be part of the answer. CLS
REFERENCES
1. Szczotka-Flynn LB,
Debanne S, Cheruvu V, et al. Predictive Factors for Corneal Infiltrates With Lotrafilcon
A Silicone Hydrogel Lenses Worn for up to 30 Nights Continuous Wear. Poster presented
at ARVO 2006. Ft. Lauderdale, Fla.
2. Jalbert I, Carnt N, Naduvilath
T, Papas E. The Relationship Between Solution Toxicity, Corneal Inflammation and
Ocular Comfort in Soft Contact Lens Daily Wear. Poster presented at ARVO 2006. Ft.
Lauderdale, Fla.
3. AC Nielsen Household Panel Surveys,
2005.
4. Fonn D. Preventing contact lens
dropouts. Contact Lens Spectrum. 2002;17:26-32.
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REFERENCES
1. Rosenthal RA, McAnally CL, et. al. High
Capacity Disinfection of Contact Lenses. Poster BCLA 2001.
2. Rosenthal R, Bell W, Schlech B. Evaluation of a New Contact
Lens Disinfectant Formulation for Disinfectant Efficacy. Poster presented at ARVO
2005. Ft. Lauderdale, Fla.
Dr.
Corbin is in private group practice near Reading, Pa. He is an adjunct professor
at Pennsylvania College of Optometry in Philadelphia.
Dr.
Lievens is an associate professor and chief of adult primary care at Southern
College of Optometry in Memphis, Tenn. He is completing a master's degree in
healthcare administration.
Dr.
Sindt is an assistant professor of clinical ophthalmology at the University
of Iowa in Iowa City, where she has practiced since 1995.
Dr.
Szczotka-Flynn is an associate professor at Case Western Reserve University
Department of Ophthalmology in Cleveland and director of the contact lens service
at University Hospitals of Cleveland. She is working on a PhD in epidemiology.
Dr.
Townsend is in a private, multi-location practice based in Canyon, Texas. He
is an adjunct professor at the University of Houston College of Optometry.
Contact Lens Spectrum, Issue: August 2006