1 & 2 step H2O2 CLs disinfection solutions against Acanthamoeba: How effective are they?

Jill Woods Jill completed her degree in Optometry & Vision Science at The City University, London, UK. She owned her own private optometry practice in London for six years. At this time she also worked in a low vision unit at Greenwich Hospital, provided clinical teaching at The City University and both practiced and taught on a voluntary basis at the London Refraction Hospital (now the Institute of Optometry). After moving to Manchester, UK she worked in several optometry practices and also taught contact lenses in the Department of Optometry and Vision Sciences at UMIST. In 1999, Jill moved to Melbourne, Australia where she managed a practice for, and became involved in clinical contact lens research with Drs Noel & Chantal Brennan. This research interest has strengthened since her move in 2005 to Waterloo, Canada where she works as a Clinical Scientist within the Centre for Contact Lens Research.

Review of paper entitled:

One- and two- step hydrogen peroxide contact lens disinfection solutions against Acanthamoeba: How effective are they?

Hiti K, Walochnik J, Faschinger C, Haller-Schober E-M and Aspock H Eye, Dec 2005; 19(12): 1301-1305

The Acanthamoeba parasite can cause some of the more tissue destructive cases of keratitis. It has the ability to adhere to soft contact lenses and in the presence of an epithelial break it can quickly attack the host cornea.  Early intervention with appropriate treatment improves the outcome of this infection and may prevent the need for corneal transplant but accurate diagnosis is frequently complex and therefore appropriate treatment can often be delayed in Acanthamoeba infections.
This paper, published in Eye, compares eleven (nine one-step and two two-step) commercially available peroxide care systems based on their ability to kill the cysts of two strains of Acanthamoeba; the 11 DS strain of Acanthamoeba hatchetti and the 1BU strain of Acanthamoeba castellanii. These particular strains had been isolated from actual patients suffering from a severe keratitis. They were carefully cultured to a mature cystic stage and then prepared as two different strength suspensions; one of 104 and another of 105 cysts/ml.

All care systems were used according to the manufacturers’ directions and the solutions were added to the Acanthamoeba suspensions in centrifugation tubes. The two-step solutions (Titmus H₂O₂ and Oxysept ® 1) were added directly to the suspensions. In the cases of the one-step systems which used a catalytic disc, the disc was inserted just prior to the addition of the 3% peroxide solution. One of the systems (Silver Sept) was tested in its original case because an integral part of the system was the silver disk attached to the lens baskets. After eight hours all samples were collected and cultured for 14 days with daily microscopic assessment to determine whether there were viable cysts present. Control samples were also prepared using sterile 0.9% sodium chloride solution.

The results of this experiment showed a clear difference in efficacy between the one-step and the two-step peroxide systems in their ability to kill the Acanthamoeba cysts; only the two-step systems (Titmus H₂O₂ and Oxysept ® 1) killed all cysts of both strains at both concentrations. This result was interesting in itself as Titmus H₂O₂ utilises peroxide in only 0.6% concentration; all the other systems use the 3% strength. The Blue Vision and AOSEPT® systems were the next most effective but they only killed the cysts of the low concentration A. hatchetti strain, not the higher concentration and not the A. castellanii strain at all. The other seven care systems (Concerto® platinum, easySEPT®, Contact care soft, Oxysept ® Comfort, ONS MERK 1, Silver Sept™ and Contopharma® peroxide) failed to completely eradicate the cysts of either strain at either concentration.

The one-step systems have been developed to overcome the risk of inserting a lens into the eye directly from the peroxide solution as this would cause significant discomfort and corneal epithelial damage. The automatic neutralising eliminates one step in the disinfecting process in an attempt to aid compliance with the system. However, placing the neutralising device, whether it is a platinum disc, catalyst tablet or neutralising solution, immediately into the peroxide solution shortens the contact time with the full strength peroxide.  It is clear from this study that this sort of convenience mechanism reduces the contact time sufficiently to render the system far less effective against the Acanthamoeba cysts.

Given that inserting peroxide into the eye can cause tissue damage that recovers fully within a day or two, whereas leaving the eye at risk to an Acanthamoeba keratitis may lead to permanent loss of vision and a corneal transplant, where is the logic of protecting against the former at the risk of facilitating the latter? Perhaps it is time that we educated our patients more fully on the risks of contact lens wear and the products available to reduce them. With the recent history of multipurpose solution recalls and incompatibilities with silicone hydrogel materials, two-step peroxide systems with their proven disinfection properties may yet prove to be the most ‘user-friendly’ contact lens care systems after all.