Ladage PM, Yamamoto K, Ren D, Cavanagh HD, et al. Effects of rigid and soft contact lens daily wear on corneal epithelium, tear lactate dehydrogenase and bacterial binding to exfoliated epithelial cells. Ophthalmology 2001;108:1279–1288.
Original study reprint requests: H. Dwight Cavanagh, Department of Ophthalmology, The University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75390–9057.
To determine the effects of lens type and oxygen transmissibility on human corneal epithelium during daily lens wear (DW).
Prospective, randomized, double-masked, single-center, parallel treatment groups clinical trial.
The University of Texas Southwestern Medical Center, Dallas, TX.
Supported in part by the National Eye Institute, Bethesda, MD; Bausch and Lomb, Inc., Rochester, New York; Menicon Ltd., Nagoya, Japan; The Pearle Vision and Chilton Foundations, Dallas, TX; Senior Scientist Awards, Olga Keith Weiss Scholar Award, and an unrestricted grant from Research to Prevent Blindness, Inc., New York, NY.
Two hundred forty-six patients were enrolled initially, after undergoing a comprehensive examination to screen for eligibility; all test groups were similar for age, gender, and refractive error. The participants were fitted with (i) high oxygen-transmissible soft lenses (n = 36), (ii) hyper–oxygen-transmissible soft lenses (n = 135), and (iii) hyper–oxygen-transmissible rigid gas-permeable (RGP) lenses (n = 75).
Pseudomonas aeruginosa binding to exfoliated corneal epithelial surface cells, central epithelial thickness, superficial epithelial cell area, epithelial surface cell exfoliation, and tear lactate dehydrogenase.
Four weeks of DW with high oxygen-transmissible soft lens significantly increased Pseudomonas binding from baseline 6.55 ± 3.01 to 8.75 ± 3.05 bacteria per epithelial cell (p < 0.01). By contrast, hyper–oxygen-transmissible soft lens wear increased binding significantly less (6.13 ± 2.45 to 7.62 ± 3.06;p < 0.01), whereas hyper–oxygen-transmissible RGP lens wear demonstrated no significant changes (5.91 ± 2.40 to 6.13 ± 2.17;p = 0.533). No significant change in central epithelial thickness was found after 4 weeks of DW in either soft lens; however, the epithelial thickness decreased by 9.8% (p < 0.001) with RGP lens wear. Epithelial cell surface area increased 3.3% and 4.1% with the high– and hyper–oxygen-transmissible soft lenses, respectively, and 10.5% with the hyper oxygen-transmissible RGP lens (p < 0.001). Epithelial desquamation significantly decreased in all groups (p < 0.001). Tear lactate dehydrogenase levels increased for all test lenses (p < 0.001).
Increased P. aeruginosa binding induced by wear of a conventional soft lens material is significantly greater than that induced by the new hyper–oxygen-transmissible soft silicone hydrogel lens during DW. However, both soft materials showed significant increases in Pseudomonas binding as compared with baseline controls. By contrast, hyper–oxygen-transmissible RGP lens DW did not increase Pseudomonas binding significantly. Taken together, these findings suggest for the first time both an oxygen effect as well as a difference between soft and rigid lens types on Pseudomonas binding in DW.
This is a well-done study evaluating the effects of daily wear soft and RGP contact lenses of various oxygen transmissibility on the ocular surface. The study is clinically relevant to understanding the pathogenesis of corneal ulcers associated with contact lenses and to what advances in technology are likely to reduce the frequency of this serious complication.
Pseudomonas corneal ulcers are one of the most serious complications associated with the use of contact lenses. Pseudomonas does not infect normal corneas, but instead requires a damaged corneal epithelium. This study shows that there is less Pseudomonas attachment to epithelial cells obtained from patients wearing higher than lower oxygen-transmissible soft contacts, but that attachment after use of both the soft contacts is significantly higher than without contacts. More interesting, however, is the finding that highly transmissible RGP lenses are not associated with increased Pseudomonas epithelial attachment over baseline without contact lenses. This suggests that, with similar oxygen-transmissible, RGP lenses will be safer than soft contact lenses. This is in keeping with our clinical experience that corneal ulcers are more frequently associated with soft than with RGP lenses of similar lower oxygen transmissibility than studied in this article.
The bottom line is that the newest soft lens materials, when used even just for daily wear, will probably still be complicated by corneal ulcers. The safest contact lens from an infection point of view remains a gas-permeable lens. It is too bad that patients don't want to wear gas-permeable lenses because of their discomfort; ideally, a gas permeable lens is comfortable as a soft lens is needed to decrease contact lens-associated infections.
It would have been interesting if the authors had obtained data on Pseudomonas attachment after a single use of these soft contact lenses. Currently, I think the safest soft contact lens is a daily disposable lens. Daily disposable lenses eliminate problems associated with compliance and efficacy of lens care regimens. It would be interesting if the data on Pseudomonas attachment were any different after 1 day compared to 2 or 4 weeks of soft contact lens use.