AIM: To investigate the safety and efficacy of undersurface ablation of the flap(UAF)for laser in situ keratomileusis(LASIK)retreatment in eyes with regression.

METHODS: Twelve patients(22 eyes)with regression after LASIK were performed undersurface ablation of the flap. The mean of preoperative refractive error was -2.27±0.88D, the astigmatism was -0.44±0.30D, the central corneal thickness was 424.9±8.2μm. The follow-up time was 1a, including visual acuity, refractive error, the elevation of posterior cornea, WavScan. The data was analyzed with Student's t test and χ² test.

RESULTS:During the operation, the measured stromal thickness was 275.4±9.3μm, the flap thickness 144.7±7.5μm, the depth of ablation 28.1±9.3μm. The mean postoperative uncorrected visual acuity(UCVA)was 4.99±0.04, best corrected visual acuity(BCVA)5.03±0.04, at 1a follow up. There was no patient with postoperative BCVA decreasing, compared to preoperation. Mean spherical refraction decreased to -0.22±0.19 D at 1a follow up(t=10.232, P<0.001)and the astigmatism decreased to -0.24±0.26 D(t=2.365, P=0.028). The elevation of posterior cornea changed from 1.95±1.68μm preoperatively to 2.00±1.88μm after 1a, but there was no statistical significance(t=0.090, P=0.929). The coma changed from 0.283±0.112μm preoperatively to 0.331±0.149μm after 1a(no statistical significance, t=1.452, P=0.161)and the spherical aberration changed from 0.320±0.119μm to 0.341±0.103μm(no statistical significance, t=0.390, P=0.674).

CONCLUSION:UAF, as one of a choice, is an effective and safe procedure for the treatment of regression after LASIK, based on the reasonable surgery design.