Differences between Regressive Eyes and Non-Regressive Eyes after LASIK for Myopia in the Time Course of Corneal Changes Assessed with the Orbscan

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Abstract
The aim of this study was to compare regressive eyes with non-regressive eyes after laser in situ keratomileusis (LASIK) for myopia with regard to the time course of biomechanical changes of the cornea and to evaluate the possible roles of these changes in refractive regression following surgery. 15 eyes of 9 patients with refractive regression and 15 eyes of 11 patients with no refractive regression after LASIK for myopia were enrolled in this study. The time courses of central corneal thickness (CCT) and anterior/posterior corneal curvature radiuses (CCR) were measured with Orbscan slit scanning before and 1 week, 1 month and 3 months after LASIK for myopia. The regressive and non-regressive eyes had similar time courses of CCT before and after LASIK, whereas the 2 groups differed in the time courses of corneal shifting movements. In the regression group, the posterior CCR after LASIK was relatively stable (all p > 0.05). By contrast, in the non-regression group, the postoperative posterior CCR at week 1 had a significantly steeper curvature than that at month 3 (p = 0.000). The anterior CCR in the regression group at week 1 had a significantly flatter curvature than that at month 3 (p = 0.002) postoperatively. In contrast, there was no significant change of anterior CCR postoperatively (all p > 0.05) in the non-regression group. Taken together, these data suggest that refractive regression after LASIK might be mainly induced by corneal protrusion rather than central corneal thickening.