Abstract
Purpose: :
To evaluate and compare the objective optical quality of the human eye using aberrometry and the modulation transfer function (MTF) after conventional laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PKR) for low to moderate myopia.
Methods: :
A retrospective analysis of 108 consecutive myopic patients who underwent refractive excimer laser treatment were evaluated. The mean spherical equivalent (SE) was lower than 6D with astigmatism less than 0.5D. Fifty-one eyes of 51 patients underwent PRK (PRK group), and 57 eyes of 57 patients underwent LASIK (LASIK group). The NIDEK-EC 5000 excimer laser was used for all treatments. For both groups, the SE, the corneal asphericity (Q factor), total and corneal aberrations were measured preoperatively and 3 months postoperatively with the OPD-Scan (NIDEK Co. Ltd., Gamagori, Japan). Root mean-square (RMS) values of total and corneal higher order aberrations out to the 6th order were compared preoperatively and postoperatively for a 6.0-mm pupil diameter. The area under the modulation transfer function (AUMTF) values were calculated and compared pre and postoperatively for higher order (HO) total and corneal aberrations. A p-value less than 0.05 was considered statistically significant.
Results: :
Postoperatively no statistically significant difference was seen for spherical equivalent (LASIK group; -0.39 +/- 0.65 D; PRK group; -0.27 D +/- 0.91 D) and the Q factor (LASIK group; +0.37+/-0.42; PRK group; +0.29 +/-0.36). Three months postoperatively, a significant increase was found for coma terms (Z3-1 ; Z31) and spherical aberration term (Z40) in both groups. No statistically significant difference was shown postoperatively between the two groups for each of the studied corneal and total eye aberration groups. The AUMTF measured with total HO aberrations was statistically higher (p = 0.04) in the LASIK group (0.242+/- 0.095) compared to the PRK group (0.213 +/-0.07). The AUMTF for corneal HO aberrations was statistically higher (p = 0.047) in the LASIK group (0.147+/-0.182) compared to the PRK group (0.105 +/- 0.032).
Conclusions: :
PRK and LASIK are both effective in reducing refractive error. Although one method uses intrastromal ablation and the other surface ablation, both tend to induce similar increases in some HO aberration terms. The AUMTF was higher after LASIK. This may indicate that better objective optical quality is obtained with LASIK.
Keywords: refractive surgery: optical quality • refractive surgery: LASIK • refractive surgery: PRK