This study aimed to investigate the effect of myopic defocus on visual acuity after phakic intraocular lens (IOL) implantation and wavefront-guided laser in situ keratomileusis (wfg-LASIK). Our prospective study comprised thirty eyes undergoing posterior chamber phakic IOL implantation and 30 eyes undergoing wfg-LASIK. We randomly measured visual acuity under myopic defocus after cycloplegic and non-cycloplegic correction. We also calculated the modulation transfer function by optical simulation and estimated visual acuity from Campbell &Green's retinal threshold curve. Visual acuity in the phakic IOL group was significantly better than that in the wfg-LASIK group at myopic defocus levels of 0, -1, and -2 D (p < 0.001, p < 0.001, and p = 0.02, Mann-Whitney U-test), but not at a defocus of -3 D (p = 0.30). Similar results were also obtained in a cycloplegic condition. Decimal visual acuity values at a myopic defocus of 0, -1, -2, and -3 D by optical simulation were estimated to be 1.95, 1.21, 0.97, and 0.75 in the phakic IOL group, and 1.39, 1.11, 0.94, and 0.71 in the wfg-LASIK group, respectively. From clinical and optical viewpoints, phakic IOL implantation was superior to wfg-LASIK in terms of the postoperative visual performance, even in the presence of low to moderate myopic regression.