Comparison of Predictability in Central Corneal Thickness Reduction After SMILE and FS-LASIK for High Myopia Correction

Abstract

Introduction: To compare central corneal thickness (CCT) reduction after small incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK) in eyes with high myopia. Methods: In this prospective, consecutive study, 70 eyes with high myopia undergoing SMILE (n = 35) or FS-LASIK (n = 35) were recruited. Corneal topography images were acquired using the Pentacam HR imaging system preoperatively and at 1 day, 1 month, and 6 months postoperatively. Predicted CCT reduction was extracted directly from the Visu-Max femtosecond laser system or MEL 80 excimer laser platform. The achieved CCT reduction was determined using corneal thickness difference maps from the Pentacam. Comparative statistics and linear regression analyses were performed to evaluate the predictability in stromal thickness reduction. Results: The mean predicted CCT reductions were 152.9 ± 6.7 lm and 150.9 ± 7.3 lm in the FS-LASIK and SMILE groups, respectively, with no statistical difference. For each follow-up time, no significant difference was noted in the two groups in the achieved CCT reduction. At 6-month follow-up, the CCT reductions were overestimated to be 23.06 ± 6.97 lm and 28.29 ± 13.92 lm in the SMILE and FS-LASIK groups, respectively (P = 0.003), showing statistical difference. Regression analysis revealed that the positive correlation between achieved and predicted CCT reductions was stronger in SMILE (R 2 = 0.5065, P \ 0.001) than in FS-LASIK (R 2 = 0.2237, P = 0.004). Overestimated CCT reduction was not correlated with predicted CCT reduction in either group. Conclusions: Systematically overestimated CCT reduction is found after SMILE and FS-LASIK in high myopia correction. Deviations between planned and achieved CCT reductions are more pronounced in FS-LASIK than in SMILE.

Comparison of planned versus achieved central corneal stromal thickness reduction in SMILE versus FS-LASIK: a retrospective study

“…Thus, calculating the corneal stromal reduction by subtracting the postoperative corneal thickness measurement from the preoperative measurement, the stromal ablation depth will be underestimated. However, due to the limitation of the diagnostic devices, some studies did not exclude the influence of epithelial hyperplasia 16 , 20 , 24 or set a constant for epithelial hyperplasia thickness to correct this bias 5 . In this study, we evaluated the thickness of the corneal epithelium and stroma separately, through which we can exclude the interference of postoperative epithelial hyperplasia thickness, thus avoiding the underestimation of the achieved central CST reduction.…”

“…The nomogram is a series of formulas that appropriately adjust a patient's manifest refraction (MR) before we input it into the laser portal software 21 – 23 . Previous studies used surgical parameters with nomogram adjustment to evaluate the accuracy of planned CT reduction, which inherently ignored the influence of nomogram 15 – 17 , 24 .…”

Corneal remodeling after SMILE for moderate and high myopia: short-term assessment of spatial changes in corneal volume and thickness

“…For a long time, the safety, stability, and effectiveness of SMILE have been a continuing concern for clinicians and patients. Studies have shown that changes in corneal volume (CV), curvature, and thickness distribution occur after SMILE for corneal remodeling [ 3 , 4 ], and these are not only important indicators for evaluating the safety and stability of refractive surgery, but also for effectively monitoring the occurrence of complications such as corneal ectasia or secondary keratoconus [ 5 – 8 ]. Therefore, the stability of CV, corneal thickness (CT) and curvature are essential for patients after SMILE.…”

“…Therefore, the stability of CV, corneal thickness (CT) and curvature are essential for patients after SMILE. Compared with patients with low myopia, patients with moderate and high myopia have a higher incidence of corneal instability and iatrogenic corneal ectasia postoperatively [ 3 ], so it is more important for them to evaluate the corneal repair and stability after SMILE. However, there are limited studies on corneal remodeling after SMILE in moderate and high myopia, and the spatial distribution of the corneal profile and its specific changes in the process of postoperative remodeling remain to be investigated.…”