Risk factors associated with contamination of orthokeratology lens cases

Purpose: To evaluate the risk factors associated with contamination of lens cases in a group of orthokeratology (ortho-k) lens wearers. Method: Ortho-k patients attending the Contact Lens Clinic of the Hospital were required to complete a checklist about their routine daily care and handling of lens cases. Their cases were then collected for analysis. Contamination was evaluated by determining the optical density (OD) of crystal violet stained biofilm present in the cases. OD values were divided into three groups, lower, middle, and upper tertiles, and associations between risk factors were determined by multivariate analysis. Results: A total of 194 subjects were recruited. Twenty-five subjects used cylindrical lens cases (CC), 98 flat cases with ridges (FCR), and 71 flat cases without ridges (FC). FCRs were the most heavily contaminated and CC showed least contamination (FCR > FC, OR 2.16, CI 1.11-4.18, p = 0.023; FCR > CC, OR 8.86, CI 2.97-26.44, p < 0.001; FC > CC, OR 2.33, CI 1.35-12.45, p = 0.013). Replacing lens cases monthly significantly reduced the risk of high contamination (OR 0.013, CI 0.06-0.30, p < 0.001), compared to those used for three months. Cases that were not rinsed (OR 3.44, CI 1.50-7.86, p = 0.003) or rinsed by other methods (OR 4.07, CI 1.67-9.92, p = 0.002) had significantly more contamination, compared to those rinsed with multipurpose solution. Lens cases, which were not dried (OR 11.36, CI 2.06-62.93, p = 0.005) or air-dried (OR 8.71, CI 1.16-65.56, p = 0.036), showed more contamination compared to those wiped with tissue daily. Conclusion: Case design (cylindrical), monthly replacement, daily rinsing with MPS, and wiping with tissue daily can effectively reduce biofilm formation in contact lens cases.