Undersurface ablation of the flap for laser in situ keratomileusis retreatment.

Abstract

To develop a novel technique, undersurface ablation of the flap (UAF), for laser in situ keratomileusis (LASIK) retreatment in eyes with insufficient posterior stroma. Noncomparative, interventional case series. From 30 eyes examined, 25 eyes with a spherical equivalent residual refraction between -0.75 and -3.25 diopters (D) and astigmatism between 0.0 and -1.5 D were prospectively included in the study. In these eyes, calculated postenhancement flap thickness was >150 micro m using micropachymetric optical coherence tomography (OCT), whereas with further ablation of the bed, posterior stromal thickness would have been <250 micro m. Primary LASIK procedures had been performed with the Hansatome microkeratome. The flap was lifted and the eye deviated downward, so that the corneal visual axis mark aligned with the laser beam. Mirror pattern ablations with an optical zone of 5 mm were performed on the flap stroma using either the Summit Apex Plus excimer laser or the Technolas Keracor 217 spot-scanning excimer laser. New axis orientation for toric ablations was calculated with the formula: beta = 180 degrees - alpha. Refraction, visual acuity, OCT pachymetry, tangential videokeratography, and patient satisfaction. The average follow-up was 6.36 +/- 2.64 months (range, 3-12 months). Mean preenhancement spherical equivalent (-2.05 +/- 0.75 D) was reduced to -0.19 +/- 0.38 D at the last visit (P = 0.001). Mean cylinder decreased from -0.48 +/- 0.53 D before retreatment to -0.23 +/- 0.28 D at the last follow-up (P = 0.003). Best-corrected visual acuity worsened by 1 line in two eyes (8%), and no eye lost 2 or more lines. Satisfactory globe stabilization and stromal smoothness during ablation were more difficult to achieve than with conventional LASIK enhancements. The average central flap thickness before UAF, 187 +/- 13 micro m, decreased to 164 +/- 12 micro m after 1 month (P = 0.001). No keratectasia developed. Finally, 92% of cases were satisfied with surgery compared with 48% before UAF retreatment (P = 0.001). UAF retreatment for low residual refractive errors after LASIK in eyes with sufficient flap stroma seems to be effective and may prevent future keratectasia.