Unwanted Astigmatism and High-order Aberrations One Year after Excimer and Femtosecond Corneal Surgery

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Abstract
Small incision lenticule extraction (SMILE) is advanced as the most minimally invasive and least traumatic corneal procedure for correcting refractive errors using a single laser. Although SMILE obtains similar results to femtosecond laser in situ keratomileusis (LASIK) with spherical myopia, it has deficiencies in astigmatism correction. The purpose of this study was to compare refractive outcomes and high-order aberrations (HOAs) between SMILE and femtosecond LASIK corneal procedures at 1 year post-operative. Ninety-two patients (181 eyes) with myopia/myopic astigmatism underwent either SMILE (group 1) or femtosecond LASIK (group 2). The refractive target was to achieve emmetropia in all cases. Data were analyzed to determine significance of change in refraction and HOAs. Furthermore, astigmatism was subjected to vector analysis using the Thibos (calculation of change, Δ, in J0 and J45 values) and Alpins (calculation of difference, ΔC, between target-induced astigmatism [TIA] and surgically induced astigmatism) methods. Forty-five patients (89 eyes) from group 1 and 47 patients (92 eyes) from group 2 completed the study. The main significant (P ≤ .001) findings were as follows: (a) residual astigmatism was greater in group 1; (b) group 1, ΔJ0 = 1.015J0 + 0.040 (R = 0.861), ΔJ45 = 1.082J45 + 0.019 (R = 0.792), ΔC = 0.401TIA + 0.323 (R = 0.489), and mean spherical aberration increased from −0.003 (SD, ±0.059; 95% confidence interval [CI], −0.015 to 0.009) to 0.028 μm (SD, ±0.041; 95% CI, −0.037 to −0.020); and (c) group 2, ΔJ0 = 0.952J0 − 0.005 (R = 0.921), ΔJ45 = 0.962J45 − 0.002 (R = 0.923), ΔC = 0.187TIA + 0.101 (R = 0.272), mean coma reduced from 0.114 (SD, ±0.087; 95% CI, 0.096 to 0.132) to 0.077 μm (SD, ±0.059; 95% CI, 0.065 to 0.089), and trefoil from 0.089 (SD, ±0.049; 95% CI, 0.079 to 0.0990) to 0.056 μm (SD, ±0.047; 95% CI, 0.046 to 0.066). In comparison with SMILE, femtosecond LASIK offered better precision in the overall control of astigmatism and HOAs.