Reader and Industry Forum

A Clinical Context for Storage Solution-Induced Staining

By Charles W. McMonnies, MSC

The use of stains to evaluate lens fit—for example, in the case of scleral and other rigid lenses—and to assess corneal and conjunctival responses to any type of contact lens wear, has a long history. The process is far from a science, however; a clinician’s judgement is always more or less required to (hopefully) make appropriate judgements regarding the clinical significance of the many forms of staining that are commonly observed.

Excellent reviews of the properties of vital stains, including their use and limitations in the assessment of the ocular surface, have been published over this time, and our knowledge of the mechanisms involved continues to increase.

Defining Solution-Induced Corneal Staining

As if the topic was not confusing enough, the recent emphasis on solution-induced corneal stain (SICS) (thoroughly examined by Jones et al [2002]) and the particular form of SICS known as preservative-associated transient hyperfluorescence (PATH) (more recently thoroughly examined by Efron [2013]), have revived memories of the staining observed and the symptoms often reported when storage solutions containing thimerosal and chlorhexidine were used to store soft lenses. PATH has been described as a transient form of SICS, a specific designation for sodium fluorescein staining that results from wearing combinations of particular lens types stored in certain brands of storage solutions. This form of staining will typically develop and dissipate within a few hours of lens application.

That SICS such as PATH may be a benign phenomenon does not really help clinicians manage their contact lens patients at aftercare visits. Even if some or all of any observed staining is PATH, and even if such staining is benign, how can a clinician know which part of the corneal staining observed is or is not related to PATH? Some or all of any observed staining may be clinically significant whether it is or is not PATH-related.

The Role of Staining in Patient Education

Research has shown that even non-contact lens wearers can exhibit some corneal staining, indicating that a certain level of staining in contact lens wearers would also be considered “normal.” Dundas et al (2001) found that some degree of fluorescent staining of the cornea was observed in 79 percent of 102 non-contact lens wearers examined on only one occasion. Schwallie et al (1997) reported a study of 16 subjects over a two-week period by two practitioners who found that the average duration of an episode of corneal fluorescent staining (median grade 0.5 using a 0 to 4 scale) was 1.2 ± 0.4 days in normal, non-lens wearers. Such staining may usually be classed as “normal” staining.

At contact lens aftercare examinations, a significant advantage of observing staining, some of which can often be classified as “normal” and non-significant, is the platform that it provides for discussing the possibility that patients’ poor compliance with contact lens care and use are related to the observed stain. Such discussion, supported by some photographs of different levels of corneal and conjunctival staining, can serve as the basis for improving patient understanding of the possible consequences of using nonprescribed care solutions, re-using care solutions, or “topping off” rather than completely replacing them, not rubbing and rinsing prior to storage, extending contact lens use beyond recommended periods, etc. This discussion and associated improved understanding of the possible consequences (associated chronic redness, lowered corneal thresholds for nociceptive perception and/or reduced tear function, with the associated possibility of increased lens awareness, etc), may result in a concomitant improvement in compliance. To that extent, the observation of staining will have been significant and useful, even if the staining can be classified as a sporadic event that is not otherwise significant.

Differentiating Normal From Notable Staining

However, aftercare examinations of contact lens wearers require that the background noise provided by “normal” staining such as may be observed in noncontact lens wearers is differentiated from any staining that is clinically significant for contact lens wearers. Begley et al (1996) examined a total of 98 hydrogel contact lens wearers at three centers and reported that the average fluorescent corneal staining grade observed was 0.5 (on a scale of 0 to 4). This average level is similar to that previously reported in non-contact lens wearers. However, one-third of the hydrogel lens wearers had “notable” staining, although that 1996 study well precedes the more recent SICS/PATH phenomenon.

Of course, “notable” staining does not depend only on the area, location, and intensity of staining; other signs, such as conjunctival hyperemia, as well as any symptoms will often help make the differential diagnosis between notable and acceptable staining. However, staining (PATH in particular) is frequently a symptomless phenomenon, at least in the short term. As yet, there does not appear to have been any examination of the long-term effects of prolonged exposure to day-to-day PATH, making it difficult to assume that it is benign.

Is SICS Related to Corneal Infiltrates?

Causes of corneal infiltrative events are not easy to determine from the many mechanisms that may be involved (including SICS). Chalmers et al (2012) reported a case-controlled study of corneal infiltrates, which found by multivariate analysis that the use of reusable soft lenses (and the need to use contact lens storage solutions) increased the risk of a corneal infiltrative event. More than 50 soft lens brands and more than 10 types of lens care products were used by the 162 patients found to have corneal infiltrates. The wide range of products used or lack of statistical power may help explain why no specific soft lens brands or lens care products were found to be associated with an increased risk of infiltrates.

What Are Practitioners to Do?

A practitioner examining a patient since the advent of PATH forms of SICS has increased chances of observing staining, but reduced chances of successful differential diagnosis. For patients who are using contact lens/care solution combinations that might induce PATH responses, scheduling patients for examination after the first few hours of lens application (by which time PATH should have dissipated) is not often practical. Similarly, asking a patient who exhibits staining to return in a few hours for re-examination to see if the suspected PATH stain persists or has dissipated is not efficient practice or convenient for the patient involved.

Not prescribing contact lens/care solution combinations that might induce PATH seems to be the more practical option, as this should eliminate one source of staining “noise” and associated potential confusion.

Another option is to avoid multipurpose solutions altogether and, as suggested by Carnt et al (2007), prescribe hydrogen peroxide disinfection. CLS

To obtain references for this article, please visit http://www.clspectrum.com/references.asp and click on document #218.

Charles W. McMonnies is an adjunct professor, School of Optometry and Vision Science, University of New South Wales. He has written three books, five text book chapters, and more than 120 scientific and clinical papers. He is a recipient of the Joseph Lederer Award and the British Contact Lens Association Medal in recognition of his contributions to contact lens education and research.