In vivo assessment of antimicrobial efficacy of silver-impregnated contact lens storage cases.

PURPOSE To evaluate microbial contamination in silver-impregnated contact lens (CL) storage cases while establishing the effect of "wet " and "dry " case maintenance and to determine its association with clinical signs, symptoms, and compliance. METHODS Two noncontemporaneous prospective studies were conducted. Regular storage cases in study 1 (n = 40) and silver-impregnated cases in study 2 (n = 41) were used in conjunction with CL solution and CLs (balafilcon A). Cases were replaced monthly and collected at 1, 3, and 4 (for silver-impregnated cases only) months. Regular cases and the fourth-month silver-impregnated cases were maintained dry, and the other cases were maintained wet between uses. At collection, storage cases were sampled and cultured for microbial identification and enumeration. Ocular clinical findings, subjective responses to CL wear, and compliance were recorded at each visit. RESULTS The percentages of microbial contamination for silver-impregnated and regular cases were 71% and 82% respectively. There were significantly (P < 0.005) fewer organisms in silver-impregnated cases (1.7 log CFU per well) than in regular cases (4.1 log CFU per well). In particular, silver-impregnated cases showed lower levels of Gram-negative bacteria (P = 0.04), Gram-positive bacilli (P = 0.03), and fungi (P = 0.006). Maintaining the silver-impregnated cases wet resulted in a lower percentage of contamination (71%; P < 0.01) than maintaining them dry (94%). There was no association between any clinical signs, symptoms, or compliance and microbial contamination of storage cases. CONCLUSIONS More than 70% of the storage cases used in daily wear CL care for a month was contaminated irrespective of the types of cases. However, silver-impregnated cases were colonized by reduced levels of Gram-negative bacteria.