Sensitive Stuff
Multipurpose solutions generally provide excellent antimicrobial activity if used according to the manufacturers’ instructions, although some struggle against certain, albeit relatively uncommon, potential pathogens such as the Gram-negative bacteria Delftia acidovorans or Stenotrophomonas maltophilia. The solutions typically contain the disinfectants polyhexanide, polyquaternium and alexidine, either alone or in various combinations, and are not required to be neutralised before the lenses are reapplied to eyes. These solutions provide relatively long-term disinfection and thus may be most appropriate for people who wear their contact lenses irregularly and so leave lenses in their contact lens cases for extended periods of time. However, people who have sensitivities to the disinfectants may struggle with these systems. For eyes with ocular surface disease, for instance, this may become an issue.
Broad-spectrum Antimicrobials
Hydrogen peroxide is also used as a contact lens disinfecting agent. This provides excellent antimicrobial activity but must be neutralised before the lenses are worn again. These days, most hydrogen peroxide solutions are neutralised during the disinfecting cycle and are called one-step systems. Another type of oxidising disinfection system like hydrogen peroxide uses iodine. Again, this is neutralised during the disinfection cycle. These disinfectants are good broad-spectrum antimicrobials that have activity even against SARS-CoV-2, the causative agent of COVID-19, in the ISO 14729 stand alone test. The oxidising agents are also effective to a large degree against Acanthamoebe cysts, something that most multi-purpose solutions are not unless the rub-and-rinse regimen is carefully followed. Once these solutions are neutralised, lenses do not contain the disinfectant when worn and so may be useful for those who have sensitivities to disinfectants. However, as the disinfectants are neutralised, if lenses are not worn at the end of the disinfection cycle or the next day, they sit in the aqueous solutions in the cases, and any remaining microbes may re-grow. Therefore, if using these systems with occasional wearers, they should be advised to go through a re-disinfection cycle prior to wear to reduce the likelihood of microbes being transferred from the cases to the lenses and then to the eye. These neutralised solutions are therefore not to be used with trial lenses either.