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FJ Stapleton, J Kasses, S Kasses, J Stern; Effect of Long-Term Wear of Highly Oxygen Permeable Contact Lenses on Corneal Epithelial Cells . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1657.
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Purpose: Continuous wear of highly oxygen permeable contact lenses appears to cause no change in shed corneal epithelial cell viability or cell size during the initial 3 months of wear. The purpose of this study was to examine shed cell size following prolonged continuous wear. Methods: 34 subjects new to contact lens wear were fitted with highly oxygen permeable contact lenses (Lotrafilcon A, Focus NIGHT & DAYTM, CIBA Vision, Atlanta, GA). Lenses were worn on a 30-night continuous wear basis. Contact lens cytology was performed prior to wear (baseline), following 1 night, 1 week, 1 month, 3 months, 6 months, 9 months, 12 months and 36 months of wear, using an etafilcon A contact lens worn for 2 minutes. Harvested corneal epithelial cells were stained using acridine orange and ethidium bromide, viewed under fluorescent microscopy and the longest cell dimension was measured for viable and non-viable cells. Alterations in epithelial cell size over time were evaluated using parametric ANOVA with multiple range testing. Results: The majority of cells recovered (≷70%) were non-viable. Significant differences in epithelial cell size were observed (p<0.01). Epithelial cell size was greater following 9 months of wear (mean 417µm) compared to baseline (mean 356µm) (p<0.05). At longer wear durations, differences from baseline were not statistically significant. Mean cell size after 36 months of wear was 364µm. Conclusion: Continuous wear of highly oxygen permeable lenses causes a slow increase in cell size over the initial 6 to 9 months of wear, which appears to reduce to baseline with longer periods of wear. We would speculate that the initial increase in cell size may be due to an inhibition of blink related shear force on the cornea, resulting in a longer cell retention time. The subsequent reduction in cell size may reflect an adaptive response to the lack of normal shear force.
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