Changes in myopia with low-Dk hydrogel and high-Dk silicone hydrogel extended wear

Purpose. This study compared changes in myopia between wearers of high-oxygen permeability (Dk) silicone hydrogel lenses and low-Dk hydrogel lenses after I year of extended wear (EW). Methods. Ninety-two adult subjects were randomly assigned to a lens type. Subjective refraction and autokeratometry were performed at baseline and at 6 and 12 months. Results. After 6 months of EW, myopia (spherical equivalent) regressed by 0.18 +/- 0.33 D (p < 0.001) in the high-Dk silicone hydrogel group and progressed by -0.23 +/- 0.36 D (p < 0.001) in the low-Dk hydrogel group. There were no further changes after 12 months. Previous lens wear history, baseline refractive error, and age and gender did not have an impact on the change in myopia, and only 35% of the variation could be accounted for by changes in corneal curvature and lens type. Conclusion. Soft contact lens type significantly affects the direction of change in myopia during EW. We hypothesize that these changes are driven by pressure-related redistribution of corneal tissue in high-Dk silicone hydrogel lens wearers and by hypoxia-associated corneal thinning in low-Dk hydrogel wearers. More long-term studies are required to confirm whether the effects of high-Dk silicone hydrogel lens wear on myopia are permanent.