The effect of cleaning and disinfection of soft contact lenses on corneal infectivity in an animal model

Animal models of bacterial keratitis

Bacterial keratitis is a disease of the cornea characterized by pain, redness, inflammation, and opacity. Common causes of this disease are Pseudomonas aeruginosa and Staphylococcus aureus. Animal models of keratitis have been used to elucidate both the bacterial factors and the host inflammatory response involved in the disease. Reviewed herein are animal models of bacterial keratitis and some of the key findings in the last several decades.

Contribution of regimen steps to disinfection of hydrophilic contact lenses

The effect of regimen steps on overall performance of contact lens disinfection processes was evaluated. Hydrophilic lenses were inoculated with Staphylococcus aureus, Pseudomonas aeruginosa, Serratia marcescens, Candida albicans, or Fusarium solani. Contributions of regimen steps and rinse volumes to disinfection abilities of OPTI-FREE EXPRESS, Solo-care Plus (Ciba Vision), Complete (Allergan), and ReNu MultiPlus (Bausch & Lomb) multi-purpose solutions were examined. Numbers of surviving microorganisms were determined. Results showed that the number and timing of regimen steps was directly related to performance of products. OPTI-FREE EXPRESS solution showed fewer survivors than did other products. Minimizing regimen steps could adversely affect product efficacy.

Effects of contact lens care solutions on surface exfoliation and bacterial binding to corneal epithelial cells

PURPOSE

The purpose of this study is to assess the effects of commercially available contact lens wetting solutions on bacterial binding and cell exfoliation rates in human corneal epithelium.

METHODS

The effects of four contact lens care solutions were tested: ReNu Multi Plus (Bausch & Lomb, Rochester, NY) multipurpose solution; OPTI-FREE Express (Alcon, Ft. Worth, TX) multipurpose solution; Complete Blink-N-Clean (Allergan, Irvine, CA) lens drops; and Lens Plus (Allergan) rewetting drops.

STUDY DESIGN

Prospective, double-masked, randomized crossover clinical trial (N = 20 subjects).

OUTCOME MEASURES

Measures of outcome included binding of Pseudomonas aeruginosa (PA) to exfoliated corneal epithelial cells, and the rate of surface cell exfoliation. Cells were collected at the baseline (pretreatment) examination and 4 days later, after subjects used the assigned solution six times daily and once again immediately before cell collection (posttreatment). Following cell collection, patients underwent 1 week of recovery, during which no drops were used, and random cross-over assignment to the next test solution.

RESULTS

Use of test solutions increased PA binding, with a range of + 11.9% to + 58.2%. Analyzed together, PA binding increased significantly (+ 29%; P = 0.02, paired t-test); Lens Plus solution alone raised PA binding levels significantly (P = 0.022, 2-way ANOVA, Student-Newman-Keuls [SNK] test). Exfoliation rates were decreased from -7% to -52.7%. Analyzed together, cell exfoliation decreased significantly (P = 0.004; Wilcoxon signed rank test). Individual use of OPTI-FREE decreased exfoliation significantly (P = 0.019: 2-way ANOVA, SNK test).

CONCLUSIONS

Topical application of common commercial contact lens care solutions increases PA binding and reduces corneal surface cell exfoliation. Similar effects have also been reported with contact lens wear. Taken together, the data suggest that the use of lens solution itself may play a role in increasing PA binding to corneal epithelial cells and, hence, might potentially contribute inadvertently to increased risk for lens-related microbial keratitis.

Assessing the in vitro cell based ocular compatibility of contact lens materials

A series of in vitro assays for determining the biocompatibility of ocular biomaterials have been developed and used to assess the differences in performance of omafilcon A, etafilcon A and nelfilcon A contact lens materials. The assays assessed bacterial attachment, macrophage adhesion, granulocyte adhesion and activation, epithelial cell adhesion and corneal cell contact damage. Overall, omafilcon A was found to be more biocompatible than the other materials although there was no significant difference between the epithelial cell adhesion and granulocyte adhesion and activation on any of the hydrogels. Etailcon A performed less well compared to nelfilcon A and omafilcon A with respect macrophage adhesion and bacterial adhesion. The results indicate that these biological assays can be successfully applied for the testing of contact lens materials and may be particularly useful in the in vitro screening of new extended wear contact lens materials where cell adhesion and activation may have a greater influence on clinical performance.