Purpose: We designed a 3-year, prospective, randomized, masked clinical trial to evaluate the relationship of contact lens oxygen transmissibility and bacterial adherence to exfoliated surface epithelial cells in human overnight and extended lens wearers in a single center; corneal cell desquamation rate, surface epithelial cell size, and tear lactate dehydrogenase (LDH) levels were also determined concurrently.
Methods: One hundred nine human volunteers were successfully fit with test lenses prospectively and completed this study. Seven soft and three rigid gas permeable (RGP) lenses with stratified oxygen transmissibility were evaluated. After one week adaptation to daily wear, patients continually wore test lenses bilaterally for three months on a six nights wear, one night off basis. Before and after 24 hour, 1 month, and three months extended contact lens wear, exfoliated surface epithelial cells were collected using a modified corneal irrigation chamber. Bacterial binding was determined by measuring Pseudomonas aeruginosa (PA) adherence to exfoliated corneal epithelial cells. The number of exfoliated cells with adherent bacteria were counted using fluorescence microscopy. The effects of contact lens wear on the corneal surface were further assessed by alterations in tear LDH, and by surface epithelial cell size and epithelial thickness using in vivo tandem scanning confocal microscopy (TSCM). Baseline values of outcome measures served as controls for individual patients; a concurrent group of controls were also followed to monitor seasonal or possible individual fluctuations.
Results: Quantitative evidence demonstrated that lens physical oxygen transmissibility properties and not lens type significantly correlated inversely with binding of PA to human exfoliated corneal epithelial cells after overnight and extended wear (R=0.258, P=0.0084); there was a significant decrease in surface epithelial cell desquamation and a significant increase in surface cell size following wear for all test lenses (P<0.05). Epithelial thinning was also observed following lens wear (P<0.05).
Conclusions: These results establish for the first time a significant correlation between contact lens-induced increases in epithelial PA binding and lens oxygen transmissibility in humans. New ultra-oxygen permeable test lenses did not appear to increase bacterial binding over individual control levels; all test lenses suppressed surface epithelial cell shedding. Taken together, these findings suggest that a new generation of contact lenses constructed from ultra-transmissible oxygen materials may offer a significant potential advance in safety for extended wear.