Disinfection of contact lenses without tap water rinsing: is it effective?
OBJECTIVE
To establish the efficacy of the two most popular contact lens disinfecting systems--one-step hydrogen peroxide and multipurpose disinfecting solution--for 1 month's use in practice in the absence of tap water rinsing.


METHODS
This was a descriptive, prospective microbiological study of contact lens contamination with ideal hygiene compliance and new lenses and storage cases. One hundred and fifty contact lens wearers were instructed to avoid risk factors identified for Acanthamoeba infection. They were randomly assigned to use one of three disinfecting systems and taught to follow manufacturers' instructions. In addition, they were taught to avoid all use of tap water for contact lens hygiene, except for hand washing.


RESULTS
There was no isolation of Acanthamoeba from any lens storage case, precluding the chance of amoebic infection. The multi-purpose solution gave the lowest rate of bacterial contamination, with 78% sterility and 15% of cases with < 10(4) bacteria/ml. For both one-step peroxide and multi-purpose solutions, Gram-negative bacteria were reduced in frequency compared with values expected historically, while Bacillus sp. were found more frequently. Storage cases of both one-step peroxide systems leaked fluid.


CONCLUSIONS
On the basis of contamination in previous studies, when hydrogen peroxide and other chemical disinfectants were used together with tap water washing, it was expected that approximately 40% of lens storage cases would yield bacteria, often with a high count, and that up to 8% would yield Acanthamoeba. Such contamination did not occur, however, in this study. The multipurpose solution, for 1 month's use, gave the lowest rate of bacterial contamination with only 7% of storage cases harbouring bacteria at > 10(4)/ml and with 78% sterility. One of the two one-step hydrogen peroxide systems performed equally well. Importantly, Acanthamoeba was not isolated from any of the 150 storage cases. Whether lens storage cases need to be sterile or contain < 10(3) bacteria/ml solution within them is debatable, but it is essential that Acanthamoeba be absent from them.
Seal
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Tennent Institute of Ophthalmology, Western Infirmary, Glasgow, UK.
Dalton
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Doris
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D000048:Acanthamoeba / Q000187:drug effects / Q000302:isolation & purification; D000818:Animals; D018639:Contact Lens Solutions / Q000494:pharmacology*; D003263:Contact Lenses, Hydrophilic / Q000382:microbiology / Q000469:parasitology; D004203:Disinfection / Q000379:methods*; D004866:Equipment Contamination / Q000517:prevention & control; D006090:Gram-Negative Bacteria / Q000187:drug effects / Q000302:isolation & purification; D006094:Gram-Positive Bacteria / Q000187:drug effects / Q000302:isolation & purification; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D006920:Hygiene; D011446:Prospective Studies; D014867:Water
D018639:Contact Lens Solutions; D014867:Water; D006861:Hydrogen Peroxide