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A.A. Alharbi, H.A. Swarbrick, D. La Hood; Overnight Orthokeratology Lens Wear Suppresses the Overnight Central Corneal Edema Response . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3704.
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Purpose:To investigate the overnight corneal edema response during overnight orthokeratology (OK). Methods: Eighteen young adult myopic subjects wore BE reverse geometry lenses in Boston XO material (nominal Dk/t 45 ISO units) on an overnight wearing schedule for 1 month. A further 10 subjects wore conventional RGP lenses of slightly higher Dk/t in one eye only on an identical schedule. Corneal thickness (total, stromal and epithelial) in the center, midperiphery and periphery was measured with the Holden-Payor optical pachometer in the morning after lens removal (am) and following 8-10 hours of no lens wear (pm), after 1, 4, 10 and 30 nights of wear. Changes from baseline (%) for OK (right eye only), RGP and no-lens eyes were compared by repeated-measures ANOVA and protected t-tests. Results: On Day 1 (am), central corneal edema averaged 1.5 ± 0.6%, 6.5 ± 0.9% and 2.7 ± 0.8% in the OK, RGP and no-lens eyes respectively (OK<RGP, p<0.01; OK<no-lens, p<0.01, unpaired t-tests). The central stroma swelled significantly less in OK than in RGP eyes (p<0.001, ANOVA), and less than with no lens wear (p<0.001, ANOVA) throughout the study. Conversely, levels of overnight edema consistent with Dk/t were found on Day 1 in the midperiphery (3.5mm from apex) and periphery (5.0mm) for both OK and RGP lenses. An overall trend suggesting adaptation of the overnight edema response was found in the midperiphery and periphery (p<0.01, regression test). Recovery to baseline stromal thickness in the evening (pm) was demonstrated for RGP eyes, and for OK eyes in the central and peripheral cornea. As reported previously, the midperipheral stroma in OK eyes showed significant residual thickening after Day 4 (p<0.001, ANOVA). Conclusions: Overnight wear of reverse geometry OK lenses suppressed the central stromal edema response. Normal overnight edema levels, consistent with Dk/t, were found in the corneal midperiphery and periphery. Adaptation of the edema response occurred with continuing overnight lens wear. We postulate that central pressure exerted by the flat-fitting base curve of the OK lens acts as a "clamp" to locally suppress central corneal swelling.
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