letters to the editor
Responding to "When Soft Toric Lens Wearers Become Presbyopic"
In the Prescribing for Astigmatism column from August 2008 titled "When Soft Toric Lens Wearers Become Presbyopic," Julie Schornack, OD, MEd, states that the current available parameters of soft toric multifocal lenses are somewhat limited, particularly for those patients who require an oblique axis. She further states that the current parameters limit the benefits of more frequent disposability. Those statements are not applicable to CooperVision's Proclear Multifocal Toric lenses.
Proclear Multifocal Toric lenses are available in sphere powers from +20.00D to –20.00D, cylinder powers from –0.75D to –5.75D, around-the-clock axes in 5-degree increments, add powers from +1.00D to +4.00D and base curves of 8.4mm and 8.8mm. Virtually any astigmatic presbyope can be fit within those parameters.
Proclear Multifocal Toric lenses are made using PC Hydrogel material, which is highly resistant to dehydration and may offer an advantage to presbyopic patients who may have increased dry eye problems as they age. As this custom-made lens is the only monthly multifocal toric disposable, it does offer all of the benefits of frequent replacement.
Harvard Sylvan, OD Director, Professional Relations CooperVision, Inc.
I enjoyed reading Dr. Julie Schornack's article, "When Soft Toric Lens Wearers Become Presbyopic." I agree with her that a large portion of our presbyopic patients have significant intermediate distance demands. However, I disagree with her that prescribing monovision is the preferred approach to correct it. I previously reported (1986, 1999) that modified monovision is a presbyopic anachronism.
I believe soft or GP contact lenses prescribed for presbyopic patients should have an aspheric posterior surface that has a conicoid design. A direct relationship exists between eccentricity values and a presbyopic correction. An ellipsoidal posterior surface furnishes near powers to +1.50D. A paraboloidal posterior surface furnishes near powers to +2.00D. A hyperboloidal posterior surface furnishes near powers to +3.00D. The progressive increases in plus powers from the center of the lens to the periphery eliminates a need to prescribe monovision.
Joe Goldberg, OD Virginia Beach, VA
Responding to "Commenting on the FDA Panel Meeting on Lens Solutions"
I just read Dr. Milton Hom's August Readers' Forum article titled "Commenting on the FDA Panel Meeting on Lens Solutions." Although Dr. Hom did not actually attend the panel meeting; I was one of the presenters and thought I would share my perspective.
In his article, Dr. Hom describes the American Academy of Optometry's statement regarding rub-and-rinse labeling presented by Dr. Charlotte Joslin. He does not, however, mention the clinically important final report on the CDC investigation of the AMO Complete MoisturePlus-Acanthamoeba outbreak presented during the panel's afternoon session.
This presentation by Jennifer Rabke Verani, MD, MPH, of the CDC's Division of Parasitic Diseases confirmed that other than topping-off old solution, patient hygiene practices played no role in either the Acanthamoeba or Fusarium outbreaks. In other words, in the two largest reported contact lens microbial keratitis case series and the only series investigated by the CDC in the past 20 years, rubbing and rinsing did not reduce the risk of infection.
While pro-rub sentiment may be increasing within the professional community, our patients have not changed their behavior. During my presentation to the panel, I shared data showing that only about half of all patients complied with rub instructions before the introduction of no-rub solutions, the same percentage after their introduction, and the same percentage even during the height of the Fusarium outbreak when media reports continually advised patients to rub and rinse.
Considering that rubbing has just been shown to have no beneficial effect in reducing the risk of infection by the US CDC and that even under the best of circumstances only half of our patients will follow written or verbal rubbing directions, we should all be asking what purpose rub-only labeling serves.
No-rub approved solutions are required to pass more rigorous disinfection efficacy testing. Setting the bar higher for solutions is also likely to fuel increased competition, spur innovation and lead to better products. Keep in mind that no-rub doesn't mean you can't rub. If a patient will benefit from rubbing, he should be instructed to rub, but he should also benefit from the most effective products possible. Contrary to what Dr. Hom suggests, rubbing does not provide a safety net. More stringent disinfection standards do.
The consensus of the FDA panel was to permit alternative care instructions such as no-rub, provided that products meet the same disinfection standards as rub-only products when used as labeled. Incidently, this was also the position of the Contact Lens Council industry group. In short, the panel did not recommend the elimination of no rub.
Dr. Hom accurately described the lack of panel consensus regarding the most appropriate time to measure corneal staining. A fixed two-hour evaluation was rejected. However, I perceived this as intent to base staining measurement upon calculated disinfectant uptake-release characteristics rather than a fixed two-hour period. It seemed clear that new test protocols would require measurement of disinfectant uptake and release; specifically its impact on disinfection efficacy and biocompatibility. It is likely that the FDA will be convening follow-up panel meetings to specifically address corneal staining and other unresolved issues.
Dr. Hom talks in his article about "leading eyecare practitioners and experts who presented that there was no evidence of a correlation between corneal staining and eventual microbial keratitis." I do not recall that from the meeting. What Dr. Hom describes as definitive evidence proving that corneal staining and microbial keratitis are unrelated is referenced in Dr. Suzanne Fleiszig's reprise of her brilliant Glenn A. Fry award lecture regarding the pathogenesis of contact lens-related keratitis, but the reference is to a single study using a mouse scarified cornea keratitis model exposed to two strains of Pseudomonas bacteria. I don't believe we can make broad definitive conclusions regarding risk of contact lens microbial keratitis in humans based on a single mouse study. Mouse corneas and human corneas are not the same, and data from two strains of a single pathogen does not provide definitive evidence regarding all possible pathogens.
Unquestionably, Dr. Fleiszig's paper is important. The essence of what she describes is that the ocular environment is exquisitely complex, and ocular defenses to infection even more so. I believe Dr. Fleiszig would agree with this broad interpretation of her paper.
Is corneal staining related to microbial infection? Although research is currently underway, we won't know for sure until all the evidence is in. However, less barrier disruption is always preferable to greater barrier disruption, and that translates to: less staining is better than more staining, and no staining is better yet.
As for Acanthamoeba, truth be told, we have a lot of work to do. No solution is completely effective against Acanthamoeba cysts. Using a novel method to compare Acanthamoeba strain differences, Shoff and colleagues found Opti-Free (Alcon) most effective against cysts, followed by ReNu MultiPlus (Bausch & Lomb), while the now-recalled Complete MoisturePlus (Advanced Medical Optics) was, as you might expect, relatively ineffective. A more recently published study by Shoff using clinical and tap water isolates found all multipurpose solutions ineffective. Clearly, testing for effectiveness against Acanthamoeba must be adopted but first, legitimate standards need to be developed and validated.
Dr. Hom and I are old friends who see eye to eye on many things. We both agree that no-rub labeling on external packaging is rapidly becoming a thing of the past. Most manufacturers have already realized that prescribing is best left to doctors and that lens care directions should not be held hostage in a game of marketing one-upmanship.
I believe we also agree that as clinicians, we must be more involved in instructing our patients about how to best care for their lenses. No one is better able to do that than a patient's practitioner. The FDA can facilitate positive patient interaction and minimize confusion by mandating that all instructions for use be removed from external lens care packaging other than to distinguish the product's purpose.
Finally, we agree that change is very much needed. I'd suggest that the best way to achieve needed change is to place patient and industry needs ahead of corporate agenda so that we can all work together for the common good. I suspect the FDA will no longer stand for anything less.
Art Epstein, OD, FAAO Roslyn Heights, NY
Dr. Epstein is a consultant for Alcon Laboratories.
Dr. Hom's Response:
I'd like to thank Dr. Epstein for his Letter to the Editor in response to my article. Dr. Epstein correctly points out that I did not attend the FDA Panel meeting. To write my article, I relied on the publicly available meeting transcripts and slides, as well as on conversations with people who were in attendance. I encourage readers to read the transcripts to form their own opinion. There are 416 pages of transcripts located at http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfAdvisory/details.cfm?mtg=699.
Dr. Epstein states, "Contrary to what Dr. Hom suggests, rubbing does not provide a safety net." The safety net concept is based on research by Shih et al (1985) and Morgan (2007) showing that more than 99 percent of the microbial bioburden is removed with rubbing. I think readers would agree that this is evidence supporting the enhanced safety of rubbing and rinsing. As a clinician, I believe that the benefits of rubbing and rinsing do not end with reduction of microorganisms; lowering deposit loads may also increase comfort and decrease dryness.
Although Dr. Epstein claims he does not recall, the transcripts of the Panel meeting show that the non-relationship between solution-related staining and microbial keratitis was well covered. I found at least six pages in the transcripts where this was discussed. As for barrier function, I am not aware of any studies connecting barrier function to the risk of microbial keratitis. Measures of increased permeability to fluid as marked with fluorescein molecules do not equate to increased permeability to microorganisms.
Dr. Epstein points out what he perceives as flaws in Dr. Fleiszig's work: mouse and human corneas are not the same. In defense of her work, I think it's very difficult to run human studies of this nature. Use of murine corneas is common in research and development. Numerous studies have used the mouse model to approximate human corneal response; a quick PubMed search found more than 900 references. On the flip side, no studies to date have disputed Dr. Fleiszig's results.
I believe that Acanthamoeba keratitis is a terrible and unfortunate disease. As recommended by the Panel, we do look to regulatory agencies to provide guidance with new standards and testing procedures for Acanthamoeba.
I have known Dr. Epstein for many years, and he always finds a way to stir someone's thinking. Our relationship reminds me of a Beatles song ("Two of Us, Let it Be"): "You and I have memories, longer than the road that stretches out ahead."
To obtain references for these letters, please visit http://www.clspectrum.com/references.asp and click on document #155.
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Contact Lens Spectrum, Issue: October 2008