DOI: 10.1097/ICL.0b013e31805cfed9
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PMID: 17630620
Issn Print: 1542-2321
Publication Date: 2007/07/01
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Excerpt
The editorial touches on specific areas that I believe raise significant clinical issues and deserve serious discussion. These relate to corneal infection rates with contact lens wear and the indiscriminate use of the term cytotoxicity when describing clinical findings such as staining of the epithelial surface with fluorescein. Furthermore, the statements concerning uptake of polyhexamethylene biguanide (PHMB) by contact lenses and the apparent effect on the cornea are speculative at best. To suggest that this may, in fact, increase the risk of infection serves to fuel speculation, which has no place in a peer-reviewed publication without scientific supporting data.
It is a worthwhile exercise to review the data associated with so-called solution cytoxicity as it relates to contact lens care products. It has been stated and reported, both anecdotally and in published reports, that low-grade clinically irrelevant corneal epithelial staining equates to solution cytotoxicity. This has been attributed to PHMB-based solutions in particular. However, peer-reviewed publications have shown that when comparing the cytotoxicity index of PHMB-preserved solutions with those preserved with POLYQUAD and ALDOX, the cytotoxicity on corneal and other standard cell lines used for these assays is consistently higher with the POLYQUAD- and ALDOX-based solutions.1–3 When considering the findings of these assays, there appears to be a disconnect between what is occurring at the cellular level with what has been interpreted clinically when using vital stains on the ocular surface. Furthermore, it is these cytotoxicity assays that are routinely used to assess the suitability of compounds and formulations for human use.
There are significant studies spanning epidemiology, basic and clinical science, and clinical observations, which challenge the speculation suggesting that PHMB-based solutions correlate with an increased risk of corneal infection in contact lens wearers. This speculation is the result of clinical observations of low levels of punctate staining at specific time points after application of lenses that have been soaking in PHMB-based solutions. The prevalence of this phenomenon differs with different lens materials and is generally characterized as being clinically insignificant. This is based on the validated 4-grade anatomic descriptive system widely used in both clinical practice and by regulatory agencies worldwide to express severity of such staining.
Considering the above, it is useful to review the peer-reviewed data that have been published to date to more clearly understand the complex relationship between contact lens wear and its relationship to infectious events. The first definitive epidemiologic study in 1989 by Schein et al.4 showed that there was an increased risk of infection from no contact lens wear versus daily wear of soft lenses. The risk was shown to be approximately 5 in 10,000 per year. This risk increased approximately five times if the lenses were worn for extended wear. In 1999 Cheng et al.,5 in a similar study, showed that the rate of infection with contact lens wear had remained constant over the intervening 10 years. If one looks at the introduction of multipurpose solutions and, in particular, those preserved with PHMB, they were introduced in 1987 and had reached approximately 50% of the market share by 1999. Despite this enormous increase in the use of these solutions, there was no concomitant increase in rates of contact lens–associated corneal infections, although low-grade staining has been reported with the use of these solutions.
