Researchers tested three types of disinfectant cleaning solution for soft contact lenses. One type was a multipurpose storage solution; the other two comprised a one step and a two step hydrogen peroxide system.
Acanthamoeba is an important cause of eye infection in contact lens wearers, with wearers of the soft type of lens most at risk. It leads to keratitis of the eye, which can be very painful and difficult to treat, and may eventually cause blindness. Poor lens hygiene is considered to be the main risk factor.
Acanthamoeba are single cell organisms with two life stages: trophozoites and cysts Disinfectant lens solutions need to be able to kill both types.
The solutions were tested against several strains of Acanthamoeba at different dilutions, for two periods of 30 minutes and 8 hours.
After 8 hours, all types of solution had killed the trophozoites of all strains. But cysts proved more of a problem. The two step 0.6% hyrdogen peroxide solution performed the best, killing virtually all cysts, and some after just 30 minutes. The multipurpose solution was less effective, but killed the cysts of at least some strains. But cysts of all strains were still viable after an 8 hour soaking with the one step 3% hydrogen peroxide solution.
Hydrogen peroxide solutions are toxic to the eye and must be neutralised. One step solutions use a catalyst to do this, and the authors suggest that the neutralisation may be too quick to prevent effective killing of the Acanthamoeba cysts.
The authors suggest that contact lens wearers choose their disinfectant solutions carefully and take additional precautions, to prevent contamination with the organisms such as microwaving, boiling, or frequently renewing, their contact lens storage cases.