17th April 2014 – New research has found that some bacteria survive hours longer in contact lens cleaning solution than was previously thought.
Each year in the UK, bacterial infections cause around 6,000 cases of a severe eye condition known as microbial keratitis – an inflammation and ulceration of the cornea that can lead to loss of vision.
The use of contact lenses has been identified as a particular risk factor for microbial keratitis, which is why cleaning is so important.
However, the British Contact Lens Association points out that there are around 3.5 million contact lens wearers in the UK and most of them experience no problems.
A quarter of all cases of bacterial keratitis are caused by the bacterium Pseudomonas aeruginosa.
Researchers from The University of Liverpool and The Royal Liverpool University NHS Trust tested different strains of Pseudomonas aeruginosa for their ability to survive in a commonly used contact lens cleaning solution.
The team compared nine clinical strains of P. aeruginosa, taken from hospital patients in the UK, with P. aeruginosa strain 9027, the standard strain used by contact lens solution manufacturers to test the efficacy of cleaning solutions.
The results showed that the majority of clinical strains tested were killed within 10 minutes of being immersed in the contact lens solution, comparable with the standard reference strain. However, one strain, P. aeruginosa 39016 – associated with a more severe case of keratitis with a prolonged healing time – was able to survive for more than 4 hours, much longer than the reference strain.
This work, presented at the Society for General Microbiology Annual Conference in Liverpool, suggests that bacterial strains with enhanced resistance should be included when testing the efficiency of contact lens cleaning solutions.
Professor Craig Winstanley, who led the research, says in a press release: "Microbial keratitis can be devastating for a patient – it is important that the risk of developing this condition is reduced in contact lens wearers by improving contact lens disinfectant solutions."
The research group now plan to investigate further to find out how widespread the enhanced bacterial resistance is and to better understand the mechanisms underlying it. It's hoped this could help in the design of more effective disinfectant procedures in the future.
This research was presented at a medical conference and has not yet undergone peer review.
Despite the new research, the British Contact Lens Association says that there has been no change in the incidence of microbial keratitis associated with contact lens wear over the years.
In a statement, the association's Howard Griffiths says: "This latest research reports the survival of one particular clinical isolate for four hours. Most patients will soak their contact lenses in contact lens solution for significantly longer than four hours and in most cases overnight, which would be sufficient to 'kill off' even the most resistant of organisms."
He says that thorough rubbing of the lens, and rinsing following the cleaning product instructions "is probably of greater importance for the removal of microorganisms from the lens, including more persistent and/or resistant clinical strains."
The British Contact Lens Association says a well known risk for microbial keratitis is failure to stick to proper lens cleaning procedures. However, it will continue to monitor the latest research to take into consideration when updating contact lens care standards.
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