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Y. Guo, T. Nguyen, S. Soni, G. Wison; Cell Shedding in Overnight Orthokeratology . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1581.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Orthokeratology produces a reduction in myopia by reshaping the cornea with specially designed rigid gas–permeable contact lenses. Central thinning of the corneal epithelium has been suggested to be one possible mechanism behind the refractive changes. Thinning could be accomplished by removal of cells from the epithelium or by redistribution within the tissue. In our study the effect of overnight orthokeratology lenses on the exfoliation of cells from the corneal epithelial surface was investigated. Methods: Ten healthy subjects between the ages of 18 and 37 years with myopia ≤ 4.00D and astigmatism ≤ 1.50D were fitted with either BE or Contex orthokeratology lenses. The lenses were worn overnight and removed during the day. The whole course of lens wear was about one month for each subject. Baseline data were collected for the week before lens wear. After 2 weeks and 4 weeks of orthokeratology lens wear cells were collected and counted again. A final collection was made after the cornea and refraction had recovered to baseline after discontinuing lens wear (usually 1 to 2 weeks). All the cell collections were made at 4 pm using flexible hydrogel contact lenses. Four insertions and removals were performed in each eye. After removal of the hydrogel lens, cells were washed from the back of the lens into a beaker. Cells from the two eyes were counted separately following fluorescent staining with acridine orange and Hoechst. Results: The refractive error was reduced significantly at day 1 and then stabilized after 1 week. The average baseline cell counts were 93±19 (mean±SEM) for nucleated cells and 209±103 for cell ghosts. No significant differences were found in the counts of cell ghosts at different time points (p > 0.05, ANOVA). However, the average counts for nucleated cells dropped significantly at 2 weeks (39±7) from the baseline (93±7), and recovered to the baseline level again by 4 weeks (p < 0.05, ANOVA). Conclusions: An increase in cell shedding from the epithelial surface is unlikely to be the explanation of thinning of the epithelium in orthokeratology. It is hypothesized that morphological restructuring of individual cells might be responsible for the short–term changes in epithelial thickness reported in orthokeratology.
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