Analysis of Higher-Order Wavefront Aberrations in Standard PRK

ABSTRACT

PURPOSE: To investigate the preoperative characteristics and postoperative change of the higher-order wavefront aberrations (HOAs) in myopic photorefractive keratectomy (PRK). METHODS: Standard PRK was performed in 39 eyes (spherical equivalent -4.71+/-1.56D) using the VISX(R) STAR S4(TM) excimer laser system. Wavefront analysis was performed preoperatively and 6 months postoperatively using the VISX(R) WaveScan(TM) aberrometer. Statistical analysis was performed to assess the preoperative characteristics of the HOAs and the PRK-induced aberrations. RESULTS: The preoperative root mean square (RMS) value of the total HOAs was 0.291 micrometer coma 0.159 micrometer, trefoil 0.157 micrometer, spherical aberration 0.093 micrometer. Among the 3 HOAs, only the spherical aberration showed moderate magnitude negative correlation with the spherical equivalent (p=0.012) and sphere (p=0.005). The magnitude of all of the HOAs, except trefoil, were significantly increased at postoperative 6 months total HOAs 183% (0.533 micrometer, p<0.001), spherical aberration 341% (0.317 micrometer, p<0.001), coma 185% (0.294 micrometer, p<0.001), trefoil 104% (0.163 micrometer, p=0.681). In the postoperative correlation analysis, only the PRK-induced spherical aberration showed the increase of magnitude with increasing preoperative spherical equivalent (p=0.036) and sphere (p=0.019). CONCLUSIONS: The HOAs, especially spherical aberration and coma, were increased after PRK. Among the 3 HOAs, the spherical aberration showed the greatest increase of magnitude and percent change; it also showed a positive correlation with increasing preoperative spherical equivalent and sphere. Further software improvements in the wavefront-guided surface ablations need to have a diminution of PRK-induced spherical aberration.