Effect of a warming device on contact lens case contamination
Related Experiment Video
Updated: May 19, 2026
Development of an In Vitro Ocular Platform to Test Contact Lenses
Published on: April 6, 2016
Mark D P Willcox1, Hua Zhu, Ajay K Vijay
1Brien Holden Vision Institute, University of New South Wales, Sydney, Australia. m.willcox@unsw.edu.au
Purpose:
To examine the effectiveness of heating contact lens cases after disinfection on reducing microbial contamination.
Methods:
One strain each of Pseudomonas aeruginosa (071) and Staphylococcus aureus (31) were used to set up robust biofilms in polypropylene contact lens cases. The effect of dilutions (from 1:10 to 1:1000) of trypticase soy broth (TSB) in phosphate-buffered saline and incubation time (24 to 48h) on the ability of strains to from biofilms with high levels of bacteria were first examined. Then the effect of increasing the temperature of incubation (from 14°C to 60°C) of biofilms during drying was examined. In the final set of experiments, biofilms of strains were subjected to heating in a warming device set to deliver 60°C for 3 hours, and the effect of this temperature after disinfection with a multipurpose disinfecting solution (MPDS; containing polyquat and Aldox) was examined by culturing the number of viable bacterial cells remaining.
Results:
A dilution of 1:100 TSB for S. aureus 31 and 1:1000 TSB for P. aeruginosa 071 together with an incubation time of 24 hours gave high numbers of viable cells of these 2 strains adhered to the contact lens cases. Having established the biofilms of bacteria, heating these to 60°C for 3 hours resulted in significant reductions in the number of viable cells that could be cultured (1 log reduction for S. aureus 31, P=0.0003; 3.5 log reduction for P. aeruginosa 071, P=0.002). Exposing the biofilms of cells to a disinfection cycle (6h at ambient temperature) in the presence of the MPDS and air drying at ambient temperature resulted in 2441±1237 colony-forming units/lens well for S. aureus 31 and 7401±4374 colony-forming units/lens well for P. aeruginosa 071. Increasing the drying temperature to 60°C resulted in zero viable cells (i.e., ≥4log reduction) for either bacterial type.
Conclusions:
Using a warming device for contact lens cases after a disinfection cycle with an MPDS during drying for 3 hours results in substantial kill of biofilms of P. aeruginosa and S. aureus that have been formed in the wells of the cases.
Insights
Heating contact lens cases after disinfection significantly reduces microbial contamination. A 60°C warming device for 3 hours eliminated viable Pseudomonas aeruginosa and Staphylococcus aureus biofilms, enhancing contact lens hygiene.
Area of Science:
- Microbiology
- Ophthalmology
- Biotechnology
Background:
- Contact lens wear is associated with microbial keratitis.
- Biofilm formation on contact lens cases poses a risk for ocular infections.
- Effective disinfection methods are crucial for contact lens hygiene.
Purpose of the Study:
- To evaluate the efficacy of heating contact lens cases post-disinfection in reducing microbial contamination.
- To determine the impact of elevated temperatures on bacterial biofilms in contact lens cases.
Main Methods:
- Established biofilms of Pseudomonas aeruginosa and Staphylococcus aureus in contact lens cases.
- Investigated optimal conditions for biofilm formation using varying nutrient broth dilutions and incubation times.
- Assessed the effect of heat (14°C to 60°C) on biofilm viability during drying.
- Examined the combined effect of a multipurpose disinfecting solution (MPDS) and heat (60°C for 3 hours) on reducing viable bacterial cells.
Main Results:
- Heating biofilms at 60°C for 3 hours significantly reduced viable cells (1 log for S. aureus, 3.5 log for P. aeruginosa).
- Disinfection with MPDS and air drying at ambient temperature left residual bacteria (2441±1237 CFU/well for S. aureus, 7401±4374 CFU/well for P. aeruginosa).
- Increasing drying temperature to 60°C eliminated all viable cells (≥4 log reduction) for both bacterial strains.
Conclusions:
- Heating contact lens cases to 60°C for 3 hours after disinfection with an MPDS effectively eliminates Pseudomonas aeruginosa and Staphylococcus aureus biofilms.
- This heating method offers a substantial reduction in microbial contamination, improving the safety of contact lens use.
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