The purpose of this article is to describe new methodology, antimicrobial efficacy endpoint methodology to determine compatibility of contact lens
solutions, lens cases and hydrogel lenses for disinfection (AEEMC), to evaluate the effect of a contact lens
and a lens case on disinfection efficacy, and to present the ring test
used to justify the use of the method in multiple laboratories.
Materials and Methods:
A prototype solution containing chlorhexidine as the disinfecting agent and four representative lens types (group I and IV hydrogels and two silicone hydrogels) were used in these ring tests
. Five laboratories participated in the chemical and microbiologic analyses. The residual chlorhexidine in lens cases containing the contact lenses was determined using high-performance liquid chromatography; uptake by the lenses was then determined by extrapolation. For the microbiologic part of the study, a contact lens
was placed in the well of the lens case, inoculated at 105
cfu (colony forming units) per lens with microorganisms in 10% organic soil. The microorganisms, Pseudomonas aeruginosa, Serratia marcescens
, Staphylococcus aureus
, Candida albicans
, and Fusarium solani
, were prepared as in International Organization for Standardization (ISO) 14729. After a 3- to 10-min exposure time, the prototype solution was dispensed into each well. Aliquots of the inoculated solutions were removed at 4 and 24 hrs and 7 and 30 days and cultured in neutralizing media for determination of survivors; lenses were also cultured for survivors.
Chemical uptake data confirmed the differences observed in kill of the challenge organisms according to lens type. It was observed that the culturing of the solution provided adequate data to show the effect of a lens on disinfection efficacy of a lens care product. The findings of the ring test
indicated that the separate culturing of the contact lenses is not necessary for routine assessment.
The methodology in the November 12, 2008, draft standard (AEEMC), meets the stated objective of demonstrating the effect of a contact lens
on the disinfection efficacy of a simulated lens care product. This method, used in combination with the methodology in ISO 14729, should provide for a more robust evaluation of applicable contact lens
care disinfecting products.