The Effect of Warming Contact Lens Disinfection Cases on Case Contamination
Mark DP Willcox, Ajay K Vijay
School of Optometry and Vision Science, University of New South Wales, Sydney,
Australia
Purpose: Contact lens cases become contaminated by a variety of microbes
during use. Up to 80% of all cases can be contaminated. Maintaining a hygienic
lens case is desirable. Epidemiology studies have demonstrated that poor lens
case hygiene is a major risk factor for microbial keratitis.
Methods: A warming device for contact lens cases has been developed. This heats
the lens cases to 60°C for 3 hours. One strain each of Pseudomonas aeruginosa
(071) and Staphylococcus aureus (31) were used to set up robust biofilms in
polypropylene contact lens cases. The biofilms were achieved by incubating cells
in dilutions of trypticase-soy broth for 24 hours. The biofilms in the cases were
challenged with the multipurpose disinfecting solution OPTIFREE RepleniSH
(containing the disinfectants polyquat and Aldox) or with heat in the presence of
the OPTIFREE RepleniSH, or were left without treatment as control cases.
Numbers of bacteria remaining in the biofilms after treatment was compared by
culturing remaining viable cells.
Results: The untreated biofilms of S. aureus contained 6.18 x 106 ± 0.74 cells and
untreated biofilms of P. aeruginosa contained 11.2 x 106 ± 4.16 cells. After
treating with OPTIFREE RepleniSH, the biofilms of S. aureus were reduced to
2.24 x 103 cells, and the biofilms of P. aeruginosa were reduced to 12.6 x 103 cells.
Using the warm contact device and heating the cases to 60oC for 3 hours resulted
in complete kill of the biofilms of both S. aureus and P. aeruginosa (i.e. >4 logs kill
compared to RepleniSH alone).
Conclusions: Heating contact lens cases for 3 hours at 60oC in the presence of a
multipurpose disinfecting solution results in much greater kill than using the
disinfecting solution alone. This may help maintain a more hygienic lens case and
so ultimately reduce keratitis associated with contact lens use.