Changes in myopic refractive error with nine months' extended wear of hydrogel lenses with high and low oxygen permeability

Background: A small but significant increase in myopia after extended wear of low oxygen permeability (Dk) hydrogel lenses has been previously reporte d; however, the specific impact of hypoxia on refractive status and corneal curvature with extended wear are not well documented. The purpose of this study was to compare the refractive changes induced over a period of 9 mont hs' extended wear with high-Dk fluorosiloxane hydrogel lenses and low-Dk hy drogel lenses. Methods: Adapted daily wear contact lens wearers were random ly assigned to one of two groups. The low-Dk group wore etafilcon A (Dk = 2 8) for up to 7 days and 6 nights and the high-Dk group wore lotrafilcon A ( Dk = 140) for up to 30 days and nights. Refractive error and corneal curvat ure were measured at 3-month intervals over 9 months of extended wear. Resu lts: The etafilcon A group demonstrated an average increase in myopia of 0. 30 D over the 9-month period; however, no change in spherical myopic correc tion was measured in the lotrafilcon A group. The cylindrical component did not change in either group. A stratified analysis revealed a greater incre ase in myopia for low myopes than moderate myopes in the etafilcon A group but no difference in the lotrafilcon A group. Keratometric analysis reveale d no change in the etafilcon A group and a small degree of central corneal flattening in both major meridians of 0.35 D in the lotrafilcon A group, Co nclusions: Nine months of extended wear of low-Dk lenses is associated with a small degree of myopic progression in adult myopes that appears to be re versible. Wearing fluorosiloxane-hydrogel lenses of high-Dk had no impact o n refractive error and may be associated with a small degree of central cor neal flattening.