Optical performance of the cornea six years following photorefractive keratectomy for myopia

Purpose. To investigate the optical quality of the anterior cornea during a 6-year follow-up after photorefractive keratectomy (PRK) for myopia.Methods. Forty-nine patients (98 eyes) underwent PRK using an excimer laser platform. Patients were subdivided into three groups according to their preoperative spherical equivalent refraction and amount of cylinder component: the low-myopia, the high-myopia, and the astigmatism group. Preoperative and 1-, 3-, and 6-year postoperative root-mean-square values of coma, spherical aberration (SA), and total high-order aberrations (HOA) were calculated over 3.50- and 6.00-mm pupil diameters. Modulation transfer function (MTF) values and point spread functions were calculated to describe the impact of myopic PRK on the optical performance of the cornea during follow-up. Results. The amount of postoperative SA was higher (P <0.05) than the preoperative state in both the low- and the high-myopia groups over 3.50- and 6.00-mm pupil sizes. The postoperative increase of coma was statistically significant (P <0.05) only in the high-myopia group over both pupil sizes. Total-HOA increased (P <0.05) after PRK in all the study groups over 6.00-mm pupil. A distinct increase in the ratios of MTF was calculated over 6.00-mm pupil, at low and middle spatial frequencies in the range between 5 and 15 cyc/deg, especially after the deepest myopic ablations. Conclusions. The high-order wave front aberration of the anterior cornea stabilized 1-year after PRK for the treatment of myopia up to -9.00 D. The effect of induced HOA on the image optical quality of the cornea was increased mainly after the correction of high myopia over scotopic pupil.