Abstract
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.
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Acknowledgements
The authors are grateful to Reza Ghaffari, MD (Farabi hospital, Tehran, Iran), Soheila Asgari, MD (Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran), and Hesam Hashemian, MD (Farabi hospital, Tehran, Iran) for collecting Corivs ST data from Noor Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran. Ali R Djalilian, MD (Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, IL) is acknowledged for his courtesy and precious comments on the present work.
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Jannesari, M., Mosaddegh, P., Kadkhodaei, M. et al. Numerical and clinical investigation on the material model of the cornea in Corvis tonometry tests: differentiation between hyperelasticity and viscoelasticity. Mech Time-Depend Mater 23, 373–384 (2019). https://doi.org/10.1007/s11043-018-9390-3
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DOI: https://doi.org/10.1007/s11043-018-9390-3