Purpose To compare the thickness and stromal optical density (OD) evolution of the flap and cap after femtosecond (FS-LASIK; Visumax) and small incision lenticule extraction (SMILE), respectively, for myopia correction. Methods A prospective study comprising 78 eyes (n=39 per group) was performed. Anterior segment optical coherence tomography (MS39) images were collected at each postoperative visit (1 day, 1 week and 1 and 3 months) and flap/cap thicknesses were measured. Using ImageJ software, three regions were defined to measure OD (in grayscale units: flap/cap stroma, residual stromal bed (RSB) and all stroma (including flap/cap-stroma, surgical interface and RSB). Results Mean central thickness significantly increased during the 3-month follow-up in both LASIK (5.43±4.23 μm; p=0.0118) and SMILE (2.76±5.61 μm; p=0.0118), with differences between both techniques statistically significant (p=0.020). All OD values showed a statistically significant reduction during SMILE follow-up: cap 48.96±5.55 versus 44.95±5.41 (p=0.19×10−6), RSB 50.26±7.06 versus 45.42±7.53 (p=0.00005), total stroma 50.34±6.49 versus 45.46±6.96 (p=0.5×10−5) at 1 day and 3 months, respectively, whereas no statistically significant changes were found during LASIK follow-up. No significant differences were observed in OD values between both techniques at any time point, although SMILE showed a tendency for higher OD values than LASIK within the first postoperative month. Visumax presented a tendency for thicker caps than target (11.48±7.85 μm), but not for flaps (2.73±8.93 μm) (p=0.00003). Conclusions Both LASIK flaps and SMILE caps show a significant postoperative rethickening. SMILE corneas present higher optical densities than LASIK corneas in the early postoperative period, with a significant decrease thereafter and up to 3 months. These findings correlate with the delayed visual recovery observed after SMILE.

中文翻译：

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激光原位角膜磨镶术与小切口微晶状体摘除近视矫正后角膜厚度和光密度的变化

目的 比较飞秒（FS-LASIK；Visumax）和小切口微透镜提取（SMILE）后皮瓣和帽的厚度和基质光密度（OD）变化，分别用于近视矫正。方法 进行了一项包括 78 只眼睛（每组 n = 39）的前瞻性研究。在每次术后访视（1 天、1 周和 1 个月和 3 个月）时收集眼前节光学相干断层扫描 (MS39) 图像，并测量皮瓣/帽的厚度。使用 ImageJ 软件，定义了三个区域来测量 OD（以灰度为单位：皮瓣/帽基质、残余基质床 (RSB) 和所有基质（包括皮瓣/帽-基质、手术界面和 RSB）。结果平均中心厚度显着增加在 LASIK (5.43±4.23 μm; p=0.0118) 和 SMILE (2.76±5.61 μm; p=0.0118) 的 3 个月随访期间，两种技术之间的差异具有统计学意义（p=0.020）。在 SMILE 随访期间，所有 OD 值均显示出统计学上显着的降低：上限 48.96±5.55 对 44.95±5.41（p=0.19×10-6），RSB 50.26±7.06 对 45.42±7.53（p=0.00005），总基质 50.34±在 1 天和 3 个月分别为 6.49 和 45.46±6.96 (p=0.5×10-5)，而在 LASIK 随访期间未发现统计学上的显着变化。在任何时间点，两种技术的 OD 值均未观察到显着差异，尽管 SMILE 显示术后第一个月内 OD 值高于 LASIK 的趋势。Visumax 呈现出比目标更厚的瓶盖趋势 (11.48±7.85 μm)，但对于襟翼 (2.73±8.93 μm) 没有 (p=0.00003)。结论 LASIK 皮瓣和 SMILE 帽均显示出显着的术后再增厚。SMILE 角膜在术后早期呈现比 LASIK 角膜更高的光密度，此后和长达 3 个月显着下降。这些发现与 SMILE 后观察到的延迟视力恢复相关。