Contact Lens Storage Case Hygiene Practice and Storage Case Contamination

Objective: Persistent microbial contamination of contact lens storage cases is common and is associated with microbial keratitis and sterile corneal infiltrates. This study investigated the ability of various currently practiced storage case cleaning techniques in the presence and absence of disinfectants to remove robust microbial biofilms. Methods: Test storage cases were inoculated with 2 mL of 108 colony-forming units per milliliter (CFU/mL) of ocular isolates of Pseudomonas aeruginosa or Staphylococcus aureus and incubated for 48 hr. Cases were subsequently treated in a variety of ways that may represent current practice including a 10-s rinse (hot water or multipurpose solution [MPS, containing PMHB and polyquaternium]), followed by air-drying for 6 hr alone, or air-drying and tissue wiping. The number of survivors was enumerated using standard culture techniques. Results: Challenge biofilms contained 8.4 +/- 0.1 log CFU (P. aeruginosa) and 7.1 +/- 0.2 log CFU (S. aureus). Rinsing with MPS or hot water and air-drying cases had no significant effect on S. aureus biofilms and resulted in only partial removal of P. aeruginosa biofilms (3.2-6.8 log CFU survivors). Rinsing with MPS, tissue wiping, and air-drying showed the greatest reduction in biofilm (0.9 +/- 0.2 log CFU survivors of P. aeruginosa and 3.4 +/- 1.2 log CFU of S. aureus). Conclusions: Biofilms formed by the S. aureus isolate were less dense but more resistant to hygiene procedures than those of the P. aeruginosa isolate. Rinsing (with MPS or hot water) followed by 6 hr of air-drying was insufficient to remove these heavy biofilms. Rinsing using the MPS followed by tissue wiping and air-drying was the most effective practice for both strains.