scholarly journals Wavefront aberrations induced from biomechanical effects after customized myopic laser refractive surgery in finite element model

2021 ◽  
Author(s):  
Ruirui Du ◽  
Lihua Fang ◽  
Weijian Peng ◽  
Ruizhi Yang ◽  
Shifeng Nie ◽  
...  
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Refractive Surgery ◽  
Element Model ◽  
High Order ◽  
Spherical Equivalent ◽  
Wavefront Aberrations ◽  
Material Parameters ◽  
Ablation Profile ◽  
High Order Aberrations

Abstract Purpose A customized myopic refractive surgery was simulated by establishing a finite element model of the human eye,after which we studied the wavefront aberrations induced by biomechanical effects and ablation profile after wavefront-guided LASIK surgery. Methods Thirty myopia patients (i.e., 60 eyes) without other eye diseases were selected. Their ages, preoperative spherical equivalent, astigmatism, and wavefront aberration were then obtained, in addition to the mean spherical equivalent error range − 4 to -8D. Afterward, wavefront-guided customized LASIK surgery was simulated by establishing a finite element eye model, followed by the analysis of the wavefront aberrations induced by the surface displacement from corneal biomechanical effects, as well as customized ablation profile. Finally, the preoperative and induced aberrations were statistically analyzed. Results Comatic aberrations were the main wavefront abnormality induced by biomechanical effects, and the wavefront aberrations induced by the ablation profile mainly included coma and secondary-coma, as well as sphere and secondary-sphere aberrations. Overall, the total high-order aberrations (tHOAs), total coma (C31), and sphere () increased after wavefront-guided customized LASIK surgery. According to our correlation analyses, coma, sphere, and total high-order aberrations were significantly correlated with decentration. Additionally, the material parameters of ocular tissue were found to affect the postoperative wavefront aberrations. When the material parameters of the sclera remained constant but those of cornea increased, the induced wavefront aberrations were reduced. Conclusion All biomechanical effects of cornea and ablation profile had significant effects on postoperative wavefront aberrations after customized LASIK refractive surgery; however, the effects of the ablation profile were more notorious.Additionally,the characteristics of biomechanical materials have influence on the clinical correction effect.

scholarly journals Biaxial estimation of biomechanical constitutive parameters of passive porcine sclera soft tissue

2021 ◽  
Author(s):  
Zwelihle Ndlovu ◽  
Dawood Desai ◽  
Thanyani Pandelani ◽  
Harry Ngwangwa ◽  
Fulufhelo Nemavhola
Keyword(s):  
Finite Element ◽  
Soft Tissue ◽  
Finite Element Model ◽  
Test Data ◽  
Element Model ◽  
Finite Element Models ◽  
Anisotropic Model ◽  
Material Models ◽  
Material Parameters ◽  
Constitutive Parameters

This study assesses the modelling capabilities of four constitutive hyperplastic material models to fit the experimental data of the porcine sclera soft tissue. It further estimates the material parameters and discusses their applicability to a finite element model by examining the statistical dispersion measured through the standard deviation. Fifteen sclera tissues were harvested from porcine’ slaughtered at an abattoir and were subjected to equi-biaxial testing. The results show that all the four material models yielded very good correlations at correlations above 96 %. The polynomial (anisotropic) model gave the best correlation of 98 %. However, the estimated material parameters varied widely from one test to another such that there would be needed to normalise the test data to avoid long optimisation processes after applying the average material parameters to finite element models. However, for application of the estimated material parameters to finite element models, there would be needed to consider normalising the test data to reduce the search region for the optimisation algorithms. Although the polynomial (anisotropic) model yielded the best correlation, it was found that the Choi-Vito had the least variation in the estimated material parameters thereby making it an easier option for application of its material parameters to a finite element model and also requiring minimum effort in the optimisation procedure. For the porcine sclera tissue, it was found that the anisotropy more influenced by the fiber-related properties than the background material matrix related properties.

Accuracy and Robustness Analysis of Geometric Finite Element Model Updating Approach for Material Parameters Identification in Transient Dynamic

2018 ◽  
Vol 16 (01) ◽  
pp. 1850084 ◽  
Author(s):  
Clément Touzeau ◽  
Benoit Magnain ◽  
Quentin Serra ◽  
Éric Florentin
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Model Updating ◽  
Numerical Test ◽  
Robustness Analysis ◽  
Element Model ◽  
Finite Element Model Updating ◽  
Transient Dynamic ◽  
Material Parameters ◽  
Material Parameters Identification

We study the accuracy and the robustness of the Geometrical Finite Element Model Updating method proposed in Touzeau et al. [Touzeau, C., Magnain, B., Emile, B., Laurent, H. and Florentin, E. (2016) “Identification in transient dynamic using a geometry-based cost function in finite element model updating method,” Finite Elements Anal. Des. 122, 49–60]. In this work, the method is applied to transient dynamic in finite transformations to identify mechanical material parameters. A stochastic approach is performed to determine accuracy and robustness. The method is illustrated on numerical test cases and compared to a classical FEMU method. Uncertainties on the loading are taken into account in the identification using an original approach.

scholarly journals The corneal biomechanical changes after SMILE and LASIK refractive surgery were compared based on finite element analysis

2021 ◽  
Vol 271 ◽  
pp. 03045
Author(s):  
Yinyu Song ◽  
Lihua Fang ◽  
Ruirui Du ◽  
Luchao Lin ◽  
Xingming Tao
Keyword(s):  
Finite Element ◽  
Refractive Surgery ◽  
Three Dimensional ◽  
Element Model ◽  
Biomechanical Properties ◽  
Stress And Strain ◽  
Wavefront Aberration ◽  
Human Cornea ◽  
Element Analysis ◽  
Wavefront Aberrations

The three-dimensional (3D) finite element model of human eye was established, and the intraocular pressure (IOP) was loaded to simulate refractive surgery. The biomechanical properties of human cornea after SMILE and LASIK surgery were studied from the stress, strain and induced wavefront aberration. Our results showed that SMILE had less impact on the biomechanics, having less stress and strain changes than LASIK. However, the stress and strain of the cornea increased with the increase of the diopter and were concentrated in the central region. We also investigated the changes in wavefront aberrations of the cornea after surgery, and the results indicated that the defocus and vertical commotion were significantly affected by SMILE and LASIK surgery, while the remaining aberrations were approximately unchanged. In conclusion, both SMILE and LASIK sergury procedures changed the postoperative corneal biomechanics, but SMILE had less impact on the biomechanics of corneal.

High order finite element model for core loss assessment in a hysteresis magnetic lamination

2009 ◽  
Vol 106 (4) ◽  
pp. 043911 ◽  
Author(s):  
Yu Zhang ◽  
Ming-C. Cheng ◽  
Pragasen Pillay ◽  
Brian Helenbrook
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Core Loss ◽  
Element Model ◽  
High Order ◽  
Loss Assessment
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