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Front Bioeng Biotechnol. 2019 May 16;7:105. doi: 10.3389/fbioe.2019.00105. eCollection 2019.

Determination of Corneal Biomechanical Behavior in-vivo for Healthy Eyes Using CorVis ST Tonometry: Stress-Strain Index.

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School of Engineering, University of Liverpool, Liverpool, United Kingdom.
St Paul's Eye Unit, Royal Liverpool and Broadgreen University Hospital, Liverpool, United Kingdom.
Department of Biomedical Science, Humanitas University, Rozzano, Italy.
Eye Center, Humanitas Clinical and Research Center, Rozzano, Italy.
Rio de Janeiro Corneal Tomography and Biomechanics Study Group, Rio de Janeiro, Brazil.
Department of Ophthalmology, Federal University of the State of Rio de Janeiro, Rio de Janeiro, Brazil.
Department of Ophthalmology and Visual Science, Department of Biomedical Engineering, The Ohio State University, Columbus, OH, United States.
NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, United Kingdom.
School of Biological Science and Biomedical Engineering, Beihang University, Beijing, China.


Purpose: This study aims to introduce and clinically validate a new algorithm that can determine the biomechanical properties of the human cornea in vivo. Methods: A parametric study was conducted involving representative finite element models of human ocular globes with wide ranges of geometries and material biomechanical behavior. The models were subjected to different levels of intraocular pressure (IOP) and the action of external air puff produced by a non-contact tonometer. Predictions of dynamic corneal response under air pressure were analyzed to develop an algorithm that can predict the cornea's material behavior. The algorithm was assessed using clinical data obtained from 480 healthy participants where its predictions of material behavior were tested against variations in central corneal thickness (CCT), IOP and age, and compared against those obtained in earlier studies on ex-vivo human ocular tissue. Results: The algorithm produced a material stiffness parameter (Stress-Strain Index or SSI) that showed no significant correlation with both CCT (p > 0.05) and IOP (p > 0.05), but was significantly correlated with age (p < 0.01). The stiffness estimates and their variation with age were also significantly correlated (p < 0.01) with stiffness estimates obtained earlier in studies on ex-vivo human tissue. Conclusions: The study introduced and validated a new method for estimating the in vivo biomechanical behavior of healthy corneal tissue. The method can aid optimization of procedures that interfere mechanically with the cornea such as refractive surgeries and introduction of corneal implants.


biomechanics; cornea; finite element modeling; material properties; numerical modeling

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