point

Solution-Induced Corneal Staining Does Matter

TOPIC: The Clinical Impact of Corneal Staining

BY LYNDON JONES, PHD, FCOPTOM, FAAO

There has been much debate about whether corneal staining associated with contact lens wear is truly relevant. Many lens wearers every day have some degree of corneal staining, which is typically asymptomatic and appears to produce no clinically relevant complications in the short-term. However, over the past 10 years, substantial evidence has demonstrated that certain combinations of lens care regimens and contact lens materials may induce excessive levels of corneal staining.

Initially, these studies reported on pHEMA-based materials and suggested that PHMB-preserved systems produced more staining than did peroxide-based systems. Jones et al (2002) demonstrated this for some silicone hydrogels when comparing PHMB to a polyquad-based system. Since that time, many publications have examined the impact of various combinations of contact lenses/lens care regimens on corneal staining, and two groups (Andrasko in the United States and the Institute for Eye Research in Australia) have attempted to systematically examine the combinations that may result in solution-induced corneal staining (SICS).

While there has been much discussion about the methods used in these various papers, there is now sufficient evidence to demonstrate that SICS does occur with certain combinations of lens materials and care regimens, although the exact mechanism and clinical relevance remains unclear. Thus, the main issues remain whether this is relevant and what to do about it.

Is Staining Relevant?

In terms of relevance, there are essentially three issues to discuss:

1. What is the impact of staining on lens comfort? The first study to discuss the staining observed between silicone hydrogels and care regimens (Jones et al, 2002) found that the degree of staining was not correlated with any significant symptoms, with no differences in lens comfort or overall preference reported between the two regimens despite marked differences in staining.

Several more recent papers have also reported the relatively asymptomatic nature of the staining. However, Jones et al noted that "stinging on lens insertion" was greatest at all clinical visits with the product that produced the greatest degree of staining. Last year Andrasko showed that there is a correlation between lens comfort and staining, with those patients exhibiting the greatest degree of staining reporting the lowest comfort.

2. What is the impact of SICS on corneal inflammation? Carnt et al (2007) demonstrated that patients who exhibited SICS were three times more likely to exhibit low grade corneal infiltrates.

3. What is the impact of SICS on microbial keratitis (MK)? Several recent papers have pointed out that to-date there is no evidence to suggest that SICS increases MK risk.

Take Action

Substantial evidence exists that certain care regimen/material combinations will induce greater-than-typical levels of corneal staining in most soft lens wearers. The exact etiology remains unclear and the long-term consequences unknown. However, given published evidence indicating that such staining can impact lens comfort and may increase the risk of subtle degrees of corneal inflammation, it would seem prudent to reduce excessive levels of corneal staining when possible.

In cases in which excessive staining does occur, you can reduce or eliminate this staining by switching to combinations of lenses and preserved care regimens that do not induce staining, by switching to hydrogen peroxide systems or by prescribing daily disposables. CLS

For references, please visit www.clspectrum.com/references.asp and click on document #159.

Dr. Jones is the associate director of the Centre for Contact Lens Research and a professor at the School of Optometry at the University of Waterloo, Ontario, Canada. He has received research funding from Alcon, AMO, B&L, CIBA Vision, CooperVision, Johnson & Johnson and Menicon.

counterpoint

Putting Solution-Induced Staining Into Perspective

BY PHILIP B. MORGAN, PHD, MCOPTOM, FAAO, FBCLA, & CAROLE MALDONADO-CODINA, PHD, MCOPTOM, FAAO

Recently, various authors (Jones et al, 2002; Andrasko and Ryen, 2007; Carnt et al, 2007) have reported solution-induced corneal staining (SICS) with some combinations of contact lenses and care systems, and their diligence in doing so should be congratulated by the contact lens community. Now that these observations have been successfully documented, we should consider the clinical relevance of corneal staining; in particular, we will address the implied concern that SICS might be a precursor to contact lens-related corneal infection, and furthermore that there might be a link between multipurpose solution (MPS) use and microbial keratitis (MK).

Literature Review

A review of the literature suggests that there is little or no evidence to support such a direct relationship. First, consider two evaluations of the incidence of MK in contact lens wearers using very similar definitions of the disease (an uncommon characteristic of contact lens epidemiological studies), reported by Poggio et al, 1989 and Cheng et al, 1999. They found very similar levels of MK in daily wear hydrogel lens wearers (i.e. solution users) despite the 10 years between the reports — a decade during which there was a significant increase in MPS use around the world at the expense of hydrogen peroxide-based products.

Second, more recent epidemiological studies also suggest no link between MPS use and infections. If MPS use was a risk factor for infection, we might expect the use of daily disposable contact lenses to be associated with a lower incidence of MK, given the reasonable similarity in the designs and materials used for daily disposable lenses and for daily wear lenses used with solutions. Recent publications (Morgan et al, 2005; Stapleton et al, 2008; Dart et al, 2008) suggest that this is not the case; indeed, Dart et al reported a higher risk of infection with daily disposable lenses than with contact lens types used with solutions.

Whilst going a step further and using epidemiology to tease out differences between solution types and rates of infection is difficult due to the small number of infections with daily wear and the ubiquity of MPSs, at least one report found a higher rate of Acanthamoeba keratitis in users of one-step peroxide products compared with MPSs (Radford et al, 2002).

Third, animal models of corneal infection with Pseudomonas suggest that it's necessary to scratch through to the stroma for an infection to occur. Removal of the corneal epithelium with filter paper (to a much greater extent than would occur in SICS, assuming that SICS represents some degree of corneal damage) followed by inoculation with bacteria does not lead to infection (Fleiszig, 2006). A related issue is that we have limited understanding of the histological changes occurring during corneal staining, so inferring a clear link between corneal staining and infection cannot be justified.

Continue With Confidence

We certainly need to better understand the nature of SICS and its implications, if any, on the health of the cornea during contact lens wear. Our clinical intuition suggests that we should avoid changes to the ocular surface during lens wear, which is an important consideration in the development of future lens care systems.

However, given that current contact lens care products, MPSs in particular, have proven to be safe (by any reasonable definition of that term), it's important that the valid debate about SICS does not serve to undermine the confidence of patients or practitioners in using MPSs for contact lens care. CLS

For references, please visit www.clspectrum.com/references.asp and click on document #159.

Dr. Morgan is director of Eurolens Research, The University of Manchester, UK. Dr. Maldon-ado-Codina is a lecturer in Optometry and Associate Director of Eurolens Research. Both have received research funding from B&L, Alcon, Johnson & Johnson, CooperVision and Sauflon Pharmaceuticals.