Corneal Asphericity and Higher-Order Aberrations after FS-LASIK and Trans-PRK for Myopia

Objective. To compare the corneal asphericity and higher-order aberrations (HOAs) of femtosecond laser-assisted in situ keratomileusis (FS-LASIK) with Smart Pulse Technology (SPT) assisted transepithelial photorefractive keratectomy (Trans-PRK) for myopia and myopic astigmatism correction. Methods. This prospective study analyzed 88 eyes of 44 patients treated with FS-LASIK and 64 eyes of 32 patients treated with Trans-PRK. All eyes had low to moderate myopia with or without astigmatism (spherical equivalent (SE) <-6.00 diopters). The uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), SE, asphericity (Q value) of the anterior corneal surface, index of surface variance (ISV), corneal higher-order aberrations (HOAs), vertical coma (Z(3)(-1)), horizontal coma (Z(3)(1)), and spherical aberration (Z(4)(0)) over a 6 mm diameter central corneal zone diameter were evaluated preoperatively and 1, 3, and 6 months postoperatively. Results. At 6 months, the UDVA and SE were -0.14 & PLUSMN; 0.06 and 0.33 & PLUSMN; 0.33D in FS-LASIK and -0.15 & PLUSMN; 0.06 and 0.35 & PLUSMN; 0.37D in Trans-PRK. There was no difference between the two groups in the postoperative UDVA and SE (P > 0.05). After FS-LASIK and Trans-PRK, the Q values in the 6, 7, 8, and 9 mm zones and ISV of the anterior corneal surface significantly increased (P < 0.001). At 1, 3, and 6 months after surgery, corneal HOA, Z(3)(-1), Z(3)(1), and Z(4)(0) in both groups were significantly increased compared with those before surgery, with statistically significant differences (P < 0.001). At 1, 3, and 6 months after surgery, the Z(3)(-1) of the Trans-PRK group was significantly lower than that of the FS-LASIK group (P < 0.001). & UDelta;HOA and & UDelta;Z(4)(0) were dramatically correlated with the & UDelta;Q value for both FS-LASIK and Trans-PRK procedures. The & UDelta;Q was significantly correlated with the preoperative SE, AD, and AD/CCT after both two procedures (all P < 0.001). Conclusions. Both FS-LASIK and Trans-PRK caused the anterior corneal surface to become flatter, and the morphology of the corneal surface was irregular. Corneal HOAs were significantly increased after the two procedures. Trans-PRK using SPT introduced less corneal vertical coma than FS-LASIK. Corneal asphericity changes contributed to the corneal aberrations changes following FS-LASIK and Trans-PRK.