Rise of contact lens-related infections warrants new look at nonbacterial causes

Kenneth R. Kenyon, MD, Editor Emeritus of the OSN Cornea/External Disease Section, addresses concerns about rising incidence of fungal and Acanthamoeba infections in contact lens users.

ByKenneth R. Kenyon, MD

Contact lens-related microbial keratitis has been a known risk since the 1980s, but it was commonly due to bacterial pathogens. Treatment with a topical antibiotic was generally effective, and the recent generations of broad-spectrum fluoroquinolones have provided “one-drop stopping” and improved prognosis for most cases.

Kenneth R. Kenyon

Yet, more recently and especially within the past 2 years, we have encountered a major shift toward nonbacterial pathogens, which are difficult both to diagnose and to treat. Thus, clinicians must increasingly suspect fungi and amoebae, as well as bacteria, in contact lens-associated keratitis.

This change of infectious etiologies surfaced in early 2006, when a cluster of contact lens- related Fusarium fungal keratitis developed in Singapore, soon to be followed by a similar multi-state outbreak in the United States. Nearly all cases were associated with the use of a specific contact lens cleaning solution, Bausch & Lomb ReNu with MoistureLoc. In May 2006, Bausch & Lomb recalled and withdrew this solution. Shortly thereafter, a rise in the incidence of contact lens keratitis caused by Acanthamoeba was related to the use of another multipurpose contact lens solution, Advanced Medical Optics Complete MoisturePlus.

Intensive epidemiologic and microbiologic studies by the manufacturers and the Centers for Disease Control and Prevention surprisingly failed to disclose contamination of the production facilities or even in-use contact lens solutions by the offending organisms. What, then, explains the mechanism of occurrence of these severe sight-threatening corneal infections? A number of possible explanations have been proposed.

Multipurpose solutions

In the presence of contact lenses, multipurpose solutions seem to have their disinfecting capability reduced. Furthermore, these formulations tend to contain components, particularly cellulose derivatives, that form films on contact lenses and lens cases and provide an excellent nutritive source for both fungi and Acanthamoeba contaminants. Furthermore, although all solutions contain biocide preservatives, such as the biguanides (eg, alexidine, chlorhexidine, PHMB), the microorganisms are then resistant to these biocides, especially if uptake of the biocide by the contact lens decreases antimicrobial activity.

The use of these biocides and/or other solution components, which are taken up by the contact lens and then released in the eye, may be causing micro-trauma to the ocular surface. More patients today are presenting with contact lens-related diffuse superficial punctate keratitis (SPK), persistent ocular surface staining and limbal stem cell damage than we had encountered in the recent past. For example, I am managing several contact lens wearers whose diffuse SPK has persisted for months after cessation of contact lens use. Such prolonged ocular surface damage is highly reminiscent of the contact lens-related superior limbic keratitis that developed in the 1980s, most probably as a consequence of thimerosal preservatives then used in contact lens solutions. In the presence of such an abnormal epithelium, a major defense mechanism of the ocular surface is compromised, as microbial adherence and penetration are facilitated.

New contact lens materials and care regimens

It is also hypothesized that there may be a block in normal inflammatory response due to stiffer materials in some current soft contact lenses. Moreover, presumably in an attempt to increase convenience, many contact lens solutions are promoted for their ease of use as “no-rub” formulations. Yet lab studies readily demonstrate that the no-rub technique also serves to further facilitate a greater buildup of pathogens on the lens surface.

Since the 1980s, various incidence, case-control and case series studies have revealed many epidemiologic factors involved in contact lens-related microbial keratitis. For example, the risk of corneal infection was increased 10-fold by extended lens wear. Selective adhesion of gram-negative bacteria to soft contact lens materials accounted for the relative increase of Pseudomonas keratitis. The use of self-made saline solution from salt tablets and exposure to amoeba-contaminated water supplies accounted for early Acanthamoeba outbreaks. Somewhat surprisingly, the wearer’s personal and contact lens hygiene habits were seldom implicated in the development of microbial keratitis, and these factors also remain uncorrelated with these recent nonbacterial infections.

‘Perfect storm’

The confluence of perhaps multiple etiologic factors resulting in this “perfect storm,” as aptly termed by Terrence P. O’Brien, MD, was, of course, wholly unsuspected. All of these lens care solutions had passed the appropriate U.S. Food and Drug Administration testing in terms of their bactericidal, fungicidal and acanthamoebacidal activities. Appropriate quality control of manufacturing facilities assured against direct contamination. Yet the several unanticipated interactions of various solution components with the lenses, the lens case and the ocular surface nonetheless combined to precipitate this clinically catastrophic storm.

Storm watch

Although these recent crisis situations have abated due to prompt and aggressive clinical recognition, astute epidemiologic study and responsible manufacturers’ actions, there inevitably remain conditions capable of provoking future “storms.” Thus, clinicians must remain with heightened awareness that these once rare birds such as fungi and Acanthamoeba are flocking more frequently.

Undoubtedly, our knee-jerk reaction to almost any contact lens-related suspected corneal infection, namely to grab a topical fluoroquinolone off the shelf for one-drop stopping, will remain the established pattern of empirical practice with typically good results. Yet in cases with atypical clinical features and inadequate response to initial antibiotic therapy, we must consider these no longer esoteric nonbacterial agents.

The use of specific culture techniques and diagnostic studies, such as high-resolution optical coherence tomography, although still largely available only in specialized practices and academic centers, are ever more mandatory to establish diagnosis and to guide therapy. There is also an ongoing need for close cooperation among clinicians, industry and contact lens users to improve contact lens products, care regimens and problem management. Such surveillance is vital to avert future overcast eyes and cloudy corneas.

For more information:

Kenneth R. Kenyon, MD, can be reached at Eye Health Vision Centers, 51 State Road, North Dartmouth, MA 02747, or Cornea Consultants International, Tal 13, 80331, Munich, Germany; 508-994-1400; fax: 508-992-7701; e-mail: kenrkenyon@cs.com. Dr. Kenyon has no direct financial interest in the products discussed in this article, nor is he a paid consultant for any companies mentioned.