Factors affecting microbial contamination on the back surface of worn soft contact lenses

Purpose: To investigate the effect of lens packaging type, the presence of chelating agent EDTA in the packaging solution and microbial contamination of the fingers on the level and rate of microbial contamination on the back surface of worn silicone hydrogel and hydrogel contact lenses. Methods: Twenty-five experienced soft contact lens wearing subjects completed each lens wear comparison. At the first two visits, participants were randomized to the lens material type to be worn bilaterally (silicone hydrogel with EDTA or hydrogel without EDTA) and the eye to which lenses removed from the two different types of lens packaging (reduced handling or conventional) was to be inserted. At the third visit, both lenses were removed from the reduced handling lens packaging and participants were randomized to wear the silicone hydrogel lens without EDTA or the hydrogel lens with EDTA in the packaging. At each visit participants washed their hands, underwent a finger swab and inserted the lenses. After 45 mins of wear, lenses were removed aseptically by a masked investigator and the lens back surface was placed on molten nutrient agar. Microbial count was conducted after 24 h. Analysis of variance and chi-square tests were conducted. Results: A total of thirty-eight subjects were enrolled: 14 males and 24 females with average age 30.9 ± 12.5 years. The multivariable analysis showed that in the presence of EDTA, conventional lens packaging was associated with a 3.38x increased risk (95%CI 1.02–11.11, p = 0.046) of lens contamination compared to the reduced handling packaging. Lens material was not significantly associated with lens contamination. In the absence of EDTA, conventional lens packaging was associated with a 3.41x increased risk (95%CI 1.02–11.36, p = 0.046) of lens contamination compared with the reduced handling packaging, but the silicone hydrogel lens material was associated with a 6.28x increased risk (95% CI 1.65–23.81, p = 0.007) of lens contamination compared with the hydrogel lens material. Finger contamination was not significantly associated with lens contamination in the presence or absence of EDTA. Conclusions: The reduced handling packaging was effective for reducing the proportion of contaminated lenses, while the presence of EDTA appeared to ameliorate this effect for silicone hydrogel lenses. Finger contamination was not associated with lens contamination.