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Numerical and clinical investigation on the material model of the cornea in Corvis tonometry tests: differentiation between hyperelasticity and viscoelasticity
Mechanics of Time-Dependent Materials ( IF 2.5 ) Pub Date : 2018-05-25 , DOI: 10.1007/s11043-018-9390-3
Mohammad Jannesari , Peiman Mosaddegh , Mahmoud Kadkhodaei , Henryk Kasprzak , Mahmoud Jabbarvand Behrouz

Non-contact tonometers, including ORA and Corvis ST, are not only used to estimate intraocular pressure (IOP) in clinical surveys but are also utilized to evaluate biomechanical properties of the cornea or anterior eye. However, for the cornea a realistic material model is still a controversial issue, and the main goal of the present study is to make this clearer. To this aim, the corneal biomechanical response is modeled by using a four-element linear viscoelastic model, which is characterized by in-vivo clinical data from Corvis ST tonometer. IOP tonometry tests on 5 normal and 5 keratoconic cases are accomplished by Corvis ST tonometer. Images from cornea deformation due to applied air jet are acquired from Corvis ST and are converted to the corneal deformation profiles by image processing techniques. By excluding the eye globe rigid body motion (retraction) from the total eye displacement, pure deformation of the cornea is obtained and used to calculate the required material properties. By calculating retardation time, contribution of the material viscosity during the test is estimated. The results show that viscosity effects do not substantially contribute to the cornea response during dynamic tests for both normal and keratoconic corneas. Indeed, the viscous effect comes from the eye globe rigid body motion.



中文翻译:

Corvis眼压计测试中角膜材料模型的数值和临床研究:超弹性和粘弹性之间的区别

非接触式眼压计,包括ORA和Corvis ST,不仅用于评估临床调查中的眼内压(IOP),而且还用于评估角膜或前眼的生物力学特性。然而,对于角膜而言,现实的材料模型仍然是一个有争议的问题,本研究的主要目的是使这一点更加清晰。为此,使用四元素线性粘弹性模型对角膜生物力学响应进行建模,该模型的特征在于来自Corvis ST眼压计的体内临床数据。Corvis ST眼压计可完成5例正常情况和5例圆锥角膜情况的IOP眼压测试。从Corvis ST获取由于施加的空气射流而产生的角膜变形图像,并通过图像处理技术将其转换为角膜变形轮廓。通过从总眼球位移中排除眼球刚体运动(回缩),可获得角膜的纯形变并用于计算所需的材料特性。通过计算延迟时间,可以估算出测试过程中材料粘度的贡献。结果表明,在正常和角圆锥形角膜的动态测试过程中,粘度效应基本上不影响角膜响应。确实,粘性效果来自眼球刚体运动。结果表明,在正常和角圆锥形角膜的动态测试过程中,粘度效应基本上不影响角膜响应。确实,粘性效果来自眼球刚体运动。结果表明,在正常和角圆锥形角膜的动态测试过程中,粘度效应基本上不影响角膜响应。确实,粘性效果来自眼球刚体运动。

更新日期:2018-05-25
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