Effects of Laser In Situ Keratomileusis and Small-Incision Lenticule Extraction on Corneal Biomechanical Behavior: A Finite Element Analysis

Abstract

Myopia, which is the result of the uncoordinated development of the eyeball, has become a major public health focus worldwide. Laser in situ keratomileusis (LASIK) and small-incision lenticule extraction (SMILE) have been successfully used in modern corneal refractive surgery. However, there are still controversies about postoperative results of LASIK and SMILE. In this study, a three-dimensional finite element model of the cornea was constructed based on the elevation and pachymetry data of a female volunteer. Surgical parameters, magnitudes of myopic correction, and intraocular pressure (IOP) were varied. Furthermore, an iterative algorithm was applied to retrieve the free-stress state of the intact corneal model, LASIK model, and SMILE model. To better evaluate the differences between LASIK and SMILE procedures, the displacement and Von Mises stress on the anterior and posterior corneal surface along the x- and y-axes were analyzed. Results for the zero-pressure model showed larger displacement compared to the image-based corneal model, suggesting that the initial corneal pre-stress stiffens the response of the cornea, both in the intact cornea and under refractive surgery. In addition, the displacement on the corneal surface in LASIK (both zero-pressure and image-based model) was obviously higher than that of the SMILE model. In contrast, SMILE increased Von Mises stress in the corneal cap and reduced Von Mises stress in the residual stromal bed compared with the LASIK model. However, the maximum Von Mises stress in the SMILE model was still smaller than that of the LASIK model. Moreover, the displacement and Von Mises stress on the residual stromal bed increased linearly with IOP. Overall, LASIK and SMILE refractive surgery could change biomechanical behaviors of the cornea. Compared to LASIK refractive surgery, SMILE may present a lower risk of ectasia. Creating a corneal cap rather than a corneal flap may have an advantage in improving corneal biomechanical stability.

Comparison of the biomechanical differences in the occlusal movement of wild-type and BMP9 knockout mice with apical periodontitis

“…According to this method, the whole structure is regarded as finite elements connected to one another, and the mechanical properties of the whole structure can be understood by studying the characteristics of each element in turn and combining the mechanical properties of each element. Due to its high feasibility, high accuracy, and low cost, FEA has been widely used as a mechanical analysis tool for the study of oral biomechanics ( Mangado et al, 2016 ; Wang et al, 2022 ). In recent years, an increasing number of studies have introduced 3D FEA into root canal therapy ( Jang et al, 2014 ; Gomes É et al, 2015 ; Askerbeyli Örs et al, 2019 ).…”

Predictive models for IOPs measured with NCT, GAT, and ORA among patients undergoing SMILE

“…There are many studies on IOP among patients undergoing laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) ( Chang and Stulting, 2005 ; Kohlhaas et al, 2006 ; Yang et al, 2006 ; Pepose et al, 2007 ; Johannesson et al, 2012 ; Han et al, 2013 ; Schallhorn et al, 2015 ; Sales-Sanz et al, 2016 ), while limited literature reports exist on predictive models of IOP changes after small incision lenticule extraction (SMILE) ( Li et al, 2016 ; Shen et al, 2016 ). As a flapless procedure utilizing a small incision, SMILE preserves the integrity of the corneal tissue (including Bowman’s layer) and serves a better corneal biomechanics than LASIK ( Wang et al, 2022 ), although it does not preserve suspect corneas before iatrogenic ectasia ( Bao et al, 2022 ; Xin et al, 2022 ). The impact of SMILE on the corneal structure prompts changes in the IOP that might differ from other refractive surgeries.…”

Strategy of Surgical Treatment of Patients with Pigment Dispersion Syndrome and Myopia

“…В случае решения вопроса о возможности проведения пациенту с СПД кераторефракционной операции (КРО) этот выбор становится еще более неоднозначным. Выполнение КРО изменяет ригидные свойства роговицы, следовательно, влияет на результат измерения ВГД по Маклакову и, таким образом, осложняет динамическое наблюдение за пациентами [6,7]. Тем не менее следует отметить, что современные диагностические приборы, такие как анализатор переднего отрезка глаза Pentacam HR (Oculus, Германия) и Visionix VX130+ (ООО «Визионикс Рус», Россия) в автоматическом режиме представляют данные результатов пневмотонометрии в зависимости от пахиметрии [8,9].…”