Effective optical zone: Differences between small-incision lenticule extraction and femtosecond LASIK for myopia

Abstract

Purpose: To compare the effective optical zones (EOZs) of small-incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (F-LASIK) by utilizing topographic methods on the tangential curvature difference map at postoperative 1 year and to identify parameters linked to the EOZ alterations following both surgeries. Methods: Myopic patients who underwent SMILE or F-LASIK were included in the study. Patients with refractive error greater than −9.0 D sphere or −0.50 D of astigmatism were excluded from the study. EOZs were measured at postoperative 1 year by using the tangential curvature difference map of the Scheimpflug tomography system. Correlations between the EOZ alterations and relevant parameters were assessed. Results: In total, 59 eyes in the SMILE group and 65 eyes in the F-LASIK group were assessed. The decrease in EOZ compared with the programmed optical zone was significantly higher in the F-LASIK group (P < 0.001). The increase in corneal asphericity was significantly relevant to the decrease in EOZin both groups according to the multiple regression analysis (P < 0.001, B/95% CI: 0.62/0.34 and 0.90, standardized-Beta: 0.587 for the SMILE group; P < 0.001, B/95% CI: 0.74/0.41 and 1.07, standardized-Beta: 0.631 for the F-LASIK group). Conclusion: The EOZ decreased 1 year after both SMILE and F-LASIK. The SMILE group showed less EOZ reduction than F-LASIK patients relative to the programmed optical zone. The decrease in EOZ was correlated with the increase in corneal asphericity in both groups.

Keywords

• corneal asphericity
• effective optical zone
• femtosecond laser-assisted in situ keratomileusis
• small-incision lenticule extraction