Investigation of predictability and influence factors of the achieved lenticule thickness in small incision lenticule extraction

Abstract

Background: To evaluate the differences between the predicted and achieved lenticule thickness (ΔLT) after small incision lenticule extraction (SMILE) surgery and investigate relationships between ΔLT and predicted lenticule thickness in SMILE. Methods: A total of 184 eyes from 184 consecutive patients who underwent SMILE were included in this prospective study. One eye for each patient was randomly selected and included for statistical analysis. To achieve emmetropia, nomogram adds 10% correction of spherical refractive. An ultrasound pachymetry measurement and Scheimpflug camera corneal topography were obtained before and at 3 months after SMILE. The achieved lenticule thickness was calculated by comparing the preoperative examinations with postoperative examinations using ultrasound pachymetry and Pentacam software measurements. The pupil center and corneal vertex were selected as the 2 locations for measurement calculation on Pentacam. Analysis of variance (ANOVA) was performed to compare mean pachymetry values using different instruments. Linear regression analyses were performed between the VisuMax readout lenticule thicknesses and the measured maximum corneal change, between ΔLT and predicted lenticule thickness. Results: On average, the achieved lenticule thickness measured with ultrasound pachymetry was 13.02 ± 8.87 μm thinner than the predicted lenticule thickness. The proportion of ΔLT in predicted values is 11.9% (ultrasound) and about 15% (Pentacam). Linear regression analysis showed significant relationships between the predicted and each achieved lenticule thickness. Each ΔLT was significantly related to predicted lenticule thickness (ultrasound: R 2 = 0.242; pupil center from Pentacam: R 2 = 0.230). Conclusions: An overestimation of achieved lenticule thickness was evident in this study which may exclude eligible SMILE patient. Also, our results showed that 10% increase of spherical refractive correction in the nomogram is appropriate. Furthermore, clinicians should subtract 10% of the predicted lenticule thickness to calculate the residual corneal stroma bed thickness.

Investigation of Accuracy and Influence Factors of Predicting Lenticule Thickness in Small Incision Lenticule Extraction by Machine Learning Models

“…In previous studies, some researchers have also found that the nomogram was not accurate. Liang et al [ 13 ] suggested adding an 11% correction of SE to the nomogram for SMILE surgery; Zhou et al [ 26 ] adjusted the mean treated SE up to −6.30 ± 2.00 D when the mean preoperative SE was −5.96 ± 1.97 D in SMILE surgery; Fang et al [ 18 ] found that the proportion of overestimation of lenticule thickness in predicted value is 11.9% for ultrasound and about 15% for Pentacam. However, previous studies were only limited to studying the overestimation rate of nomogram and obtained a more accurate estimate value by reducing a certain proportion of nomogram; few studies had constructed a model to predict LT from the major factors affecting LT.…”

“…However, there was no comparison with the other algorithms in their study, and this study focused more on reducing the postoperative refractive error than the lenticule thickness error. Fang et al [ 18 ] found that the lenticule thickness predicted by the nomogram exceeds the achieved lenticule thickness by approximately 10%, but it’s just a correction.…”

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

“…First, CCT reduction was overestimated at approximately 23 μm 6 months after SMILE, which was concordant with the results of previous studies. According to several previous studies, CCT reductions could be overestimated at approximately 15–18 μm when examined by Pentacam imaging and approximately 13–24 μm by optical coherence tomography (OCT) after SMILE [ 6 , 9 , 12 , 13 ]. Corneal remodeling pattern was hypothesized as an influencing factor causing the discrepancy between predicted and achieved CCT reductions.…”

“…Moreover, as attempted SE correction increased, more corneal stromal tissues were removed, and stronger corneal stromal expansion strength was observed. In a study evaluating the difference in CCT reduction after SMILE in various degrees of myopia, the deviations were 20.08 ± 6.84 μm and 7.20 ± 10.50 μm in the high and low myopia groups, respectively [ 13 ]. Notably, our study included eyes with myopia more than − 9.0 D, and the deviation was larger than that of the former study, further supporting Reinstein et al’s hypothesis.…”

“…Wu et al evaluated the agreement between predicted and measured CCT reductions after SMILE and FS-LASIK. They concluded that both procedures overestimated CCT reduction, and that no statistical difference existed between the two procedures (16.40 ± 9.35 μm for FS-LASIK vs. 14.95 ± 8.10 μm for SMILE) [ 13 ]. Lazaridis et al proposed the higher deviation in CCT reduction after FS-LASIK compared to after SMILE (31 μm vs. 16 μm) [ 7 ].…”