Wavefont Analysis of Flap and Laser-Induced Aberrations in a Two-Step LASIK Procedure

Abstract

Abstract: : Purpose:To identify aberrations created by making a LASIK flap and by treating the refractive error with a flying-spot laser. Methods:Twenty-two eyes underwent a two-step LASIK procedure with the Autonomus LADARVision laser. In the first step a flap was made, and 1 month later it was lifted and the laser correction was done. Aberrations were measured with the LADARWave wavefront measurement device pre-operatively, after making the flap (1 day, 1 week, 1 month post flap) and after laser treatment (1 week, 3 months post laser). Two different microkeratomes were used (Moria M2 and SKBM). With SKBM all flaps were nasal, with Moria M2 the flap was randomly selected as superior or nasal. Results: The difference between the preoperative and post-flap measurements for lower and higher order aberrations was not statistically significant for the two types of microkeratomes used and for hinge position placement. A slight hyperopic shift after making the flap was noted in the manifest refraction and in the wavefront refraction. Manifest sphere and cylinder, wavefront sphere and cylinder and defocus decreased significantly after laser ablation, but there was no statistically significant difference between preoperative and post-flap measurements. When analyzing higher order aberrations, the only component that showed significant difference between preoperative and post-flap values was other higher order terms at 1 day post-flap (p=0.001). All higher order aberrations showed statistically significant increment between preoperative and post-laser treatment. Conclusions: Making the flap creates changes in the aberrations, but these changes seem to be transitory and not significant, returning close to pre-operative levels 1 month later. This data suggests that customized laser treatment as a two step procedure may not be necessary. Laser treatment increases aberrations, especially spherical aberration, and these changes seem to be stable and permanent after 3 months.

Keywords: refractive surgery: LASIK • refractive surgery: optical quality