Revisiting Hydrogen Peroxide Disinfection
BY MICHAEL A. WARD, MMSC, FAAO
Hydrogen peroxide disinfecting systems offer antimicrobial efficacy without the use of preservatives. Microfiltered, stabilized and buffered 3% hydrogen peroxide is the active ingredient in peroxide-based systems. It's effective against a wide variety of organisms: bacteria, fungi (including spores and yeasts), viruses and some protozoa. Hydrogen peroxide destroys pathogens by oxidation, which results in protein denaturation, and by damaging microbial cell membranes.
Approximately 10 minutes at full strength exposure is necessary to eliminate most bacteria. Fungi and protozoa require longer contact times at full 3% H2O2 strength. Unlike multipurpose solution disinfectants, hydrogen peroxide is unaffected by the presence of organic matter or salts and can penetrate most microbial biofilms.
The hydrogen peroxide in these systems must be neutralized prior to lens wear as unneutralized peroxide is toxic. Two methods of peroxide neutralization are available: catalase enzyme and catalytic disc.
Two System Types
UltraCare (AMO) is a one-step peroxide system that uses the enzyme catalase to neutralize the hydrogen peroxide. In this system, a catalase-neutralizing tablet is added to the lens case at the same time as the peroxide disinfectant solution. The catalase-based neutralizing tablet is encapsulated with hydroxypropyl methylcellulose (HPMC), which time-delays the neutralizer, thus allowing a controlled exposure time for the disinfectant.
HPMC also acts as a lubricant dissolved in the storage solution. Cyanocobalamin (vitamin B12) creates a pink hue to indicate that the neutralizing tablet has been added to the system.
ClearCare (CIBA Vision) is a one-step system that uses a platinum-coated plastic disc to catalyze the breakdown of the hydrogen peroxide to oxygen and water. Depending on the age of the disc, the neutralization may occur in a few minutes or in several hours. A fresh disc neutralizes the peroxide quickly, thus rapidly decreasing the concentration and contact time for antimicrobial activity, but providing a more thorough neutralization; an old disc provides a longer contact time with higher concentrations of peroxide, but with less effective neutralization.
There are two potential pitfalls for patients using peroxide based disinfectants: toxic keratitis and contamination of the unpreserved storage solution.
Occasionally patients using peroxide-based systems may place a lens on the eye that has been bathed in unneutralized peroxide. Fortunately, this type of chemical burn, although painful, is superficial and self-limiting.
Another potential concern with hydrogen peroxide disinfection is the potential for contamination of lenses stored in neutralized peroxide solution.
Although hydrogen peroxide systems have high antimicrobial efficacies at full strength, once neutralized they become unpreserved aqueous bathing solutions capable of supporting microbial growth. Non-preserved peroxide systems work fine if used on a regular, preferably daily basis. However, if lenses have been soaking in the neutralized solution for longer than one day, we recommend that the disinfecting/neutralization procedure be repeated prior to lens wear.
Patients should also pay attention to the inside of the lens case cap as little or no disinfection occurs on these surfaces. Patients can disinfect the inside cap by inverting the lens case filled with fresh peroxide. Patients should follow the instructions of the individual system.
Mr. Ward is an instructor in ophthalmology at Emory University School of Medicine and Director, Emory Contact Lens Service.