David McCanna, PhD is a Research Associate and Adjunct Professor of Immunology at the University of Waterloo. Before completing his PhD in Vision Science and Biology at the University of Waterloo, he worked as a manager and research scientist at Bausch & Lomb.The maintenance of a clean lens case is essential for preventing contamination of contact lenses from pathogenic organisms. There are a wide variety of contact lens care solution products that can be used to clean and disinfect contact lenses. These multi-purpose solutions contain antimicrobials that kill Gram-negative and Gram-positive bacteria, yeast, fungi and protozoan parasites. Although these solutions have been shown to be effective in laboratory-based studies, many contact lens care solution products are not effective at preventing contact lens cases from becoming contaminated. The following is a review of a recently published article determining the efficacy of contact lens disinfecting solutions.
Willcox M D P, Carnt N, et al. (2010). Contact lens case contamination during daily wear of silicone hydrogels. Optometry & Vision Science 87(7): 456-464.
Willcox and colleagues performed a clinical study with 232 participants. After one month of using various silicone hydrogel lenses and disinfecting solutions, lens cases were evaluated to determine the number of contaminated lens cases and the types of microorganisms present.
Method of assessing lens case contamination
After discarding the disinfecting solution, the microorganisms were removed from the lens case lids and wells by wiping these surfaces with alginate swabs. These organisms were then grown on culture media to determine the number of microorganisms present. Media and growth conditions were optimized to assure the detection of aerobic and anaerobic bacteria, yeasts, molds and the protozoa Acanthamoeba.
Efficacy of contact lens care solutions
Four different contact lens care solutions were evaluated. These solutions contained either polyhexanide (PHMB) solution (AQuify), hydrogen peroxide (Clear Care), or polyquaternium-1 with myristamindopropyl dimethylamine (Opti-Free Express and Opti-Free RepleniSH) as disinfecting actives.
With contamination defined as the detection of at least one colony-forming unit from the lens case, the overall rate of contamination of the lens cases was 85%. The highest number of contaminated lens cases occurred with AQuify (92%) and the lowest with Opti-Free Express (76%).
Microorganisms identified from lens cases
The microorganisms identified from these lens cases included Gram-positive bacteria, Gram-negative bacteria and fungi.
- There was a higher rate of contamination and higher numbers of Gram-negative bacteria in lens cases exposed to Opti-Free RepleniSH than lens cases exposed to the other contact lens care solutions.
- More Gram-positive organisms contaminated cases exposed to AQuify and ClearCare solutions than either Opti-Free Express or Opti-Free Replenish solutions.
Some of the microorganisms that contaminated these lens cases are listed below.
Gram-negative organisms:
– Delftia acidovorans
– Serratia marcescens
– Achromobacter
– Stentotrophomonas maltophilia
– Pseudomonas aeruginosa
– Corynebacterium
Gram-positive organisms:
– Staphylococcus aureus
– Staphylococcus epidermidis
– Staphylococcus saprophyticus
– Micrococcus
– Propionibacterium
Conclusion
The microorganisms that can cause corneal infiltrative events during contact lens wear could come from contaminated contact lens cases. Willcox and colleagues have demonstrated that a wide variety of microorganisms adhere to and colonize lens cases. Using the methods utilized in this investigation, new antimicrobial lens cases and contact lens solutions will be able to be evaluated for determining their efficacy against microorganisms that colonize lens cases.
