Numerical and clinical investigation on the material model of the cornea in Corvis tonometry tests: differentiation between hyperelasticity and viscoelasticity

Jannesari, Mohammad; Mosaddegh, Peiman; Kadkhodaei, Mahmoud; Kasprzak, Henryk T.; Behrouz, Mahmoud Jabbarvand

doi:10.1007/s11043-018-9390-3

Cited by 14 publications

(16 citation statements)

References 32 publications

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“…Findings of our work may impact the results of various clinical studies that have utilized uncorrected air puff load values to monitor KCN ( Tian et al, 2014 ; Elham et al, 2017 ), evaluate corneal crosslinking ( Bak-Nielsen et al, 2014 ; Tian et al, 2014 ), assess the risk of refractive surgery ( Kataria et al, 2019 ), assess corneal response pre/post refractive surgery ( Pedersen et al, 2014 ; Frings et al, 2015 ; Sefat et al, 2016 ; Xu et al, 2017 ), or compare different methods of refractive surgery ( Pedersen et al, 2014 ; Sefat et al, 2016 ). Furthermore, the significant change in the air puff load as a response to the deformed corneal surface is neglected in many modeling studies of noncontact corneal deformation ( Francis et al, 2019 ; Jannesari et al, 2019 ). Although a previous modeling study reported changes in the fluid dynamics characteristics as the cornea deformed, the specifics of these changes were not quantified ( Kling et al, 2014 ).…”

Section: Discussionmentioning

confidence: 99%

The Shape of Corneal Deformation Alters Air Puff–Induced Loading

Yousefi

Roberts

Reilly

2022

Front. Bioeng. Biotechnol.

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Purpose: To determine the dynamic modification of the load exerted on the eye during air-puff testing by accounting for the deformation of the cornea.Methods: The effect of corneal load alteration with surface shape (CLASS) was characterized as an additional component of the load produced during the concave phase where the fluid outflow tangential to the corneal surface creates backward pressure. Concave phase duration (tCD), maximum CLASS value (CLASSmax), and the area under CLASS-time curve (CLASSint) are calculated for 26 keratoconic (KCN), 102 normal (NRL), and 29 ocular hypertensive (OHT) subjects. Tukey’s HSD tests were performed to compare the three subject groups. A p-value less than 0.05 was considered statistically significant.Results: Accounting for CLASS increased the load by 34.6% ± 7.7% at maximum concavity; these differences were greater in KCN subjects (p < 0.0001) and lower in OHT subjects (p = 0.0028) than in NRL subjects. tCD and CLASSint were significantly longer and larger, respectively, for KCN subjects than those in the NRL and OHT groups (p < 0.0001).Conclusion: Load characterization is an essential step in assessing the cornea’s biomechanical response to air-puff–induced deformation. The dynamic changes in the corneal surface shape significantly alter the load experienced by the corneal apex. This implies a subject-specific loading dynamic even if the air puff itself is identical. This is important when comparing the same eye after a surgical procedure or topical medication that alters corneal properties. Stiffer corneas are least sensitive to a change in load, while more compliant corneas show higher sensitivity.

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Section: Discussionmentioning

confidence: 99%

The Shape of Corneal Deformation Alters Air Puff–Induced Loading

Yousefi

Roberts

Reilly

2022

Front. Bioeng. Biotechnol.

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“…To present a quantitative comparison, a set of dynamic corneal deformation parameters was selected from Corvis-ST analysis of patient data, namely: peak distance (PD), radius of curvature at highest concavity (HCR), and maximum apical displacement (MAD). Following the study by Jannesari et al [17], the retraction of the eyeball was calculated, and the pure corneal clinical deformation responses along with corresponding values from the developed a FEM for each surgical scenario were obtained, as listed in Table 3. In addition, keratometry values were generated for each surgical scenario to obtain a correlation of the corneal deformation behavior along with the shape regularization effect.…”

Section: Effect Of Icrs On Corneal Deformations and Shape Regularization (Fem Validation)mentioning

confidence: 99%

“…Among numerical studies on biomechanical behavior of the cornea subjected to air-puff test [13,14], Francis et al [15] reported a better biomechanical outcome after small incision lenticule extraction (SMILE) and laser-assisted in situ keratomileuses (LASIK) than after photorefractive keratectomy (PRK), while SMILE left the residual cornea biomechanically stiffer than LASIK. Several studies have been conducted to evaluate the corneal material properties considering NCT, based on mechanical finite-element analysis (FEA) [13,[16][17][18] and uid-solid interactions modeling [19,20]. Muench et al [21] investigated shear stress profiles on the cornea exposed to air-puff test using computational fluid dynamics (CFD) modeling.…”

Section: Introductionmentioning

confidence: 99%

Effects of intracorneal ring segments on the biomechanical response of the ectatic cornea to air-puff: A patient-specific numerical analysis

Bagheri

Mosaddegh

Kadkhodaei

2021

Mathematics and Mechanics of Solids

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The assessment of the underlying factors that influence the biomechanics and dynamics of the cornea is essential for preserving the safety and efficacy of refractive surgeries. In the present work, the operated cornea with intracorneal ring segments (ICRSs) in a patient-specific finite-element model (FEM) was subjected to the air-puff. Then, the dynamic deformation parameters predicted by the FEM were obtained and compared with the corresponding values in clinical measurements. In this study, the effects of ICRS design, position, and implementation procedure in six different surgical scenarios were examined on the induced corneal stresses, deformation behavior, and shape regularization. While surgical scenarios with arc lengths of 160° (single and double segment), 355° implemented with the tunnel incision method provided similar maximum apical displacement (MAD) and highest concavity radius of curvature HCR), they induced significantly different flattening effects. The surgical scenarios with the segment of 160° arc-length implemented in nasal–temporal direction showed an approximately 15% higher reduction in mean corneal power ([Formula: see text]) value than the superior–inferior direction. From a solid-mechanics perspective, the study of ICRS mechanics in the cornea also confirmed the importance of the implementation position to achieve satisfactory flattening outcomes. Comparison of the two types of ICRS implementation procedures showed that, although the pocket method demonstrated a 10.23% higher MAD, it induced a higher reduction in the HCR of 21.65% compared with tunnel incision. The developed numerical model demonstrated the direct correlation of the ICRS insertion site with induced contact stresses and ICRS position stability. The study hypothesizes the significant influence of ICRS implementation position and procedure on the corneal biomechanical and dynamical behaviors. The proposed approach can be assessed as a robust and novel framework for planning optimized corneal refractive surgeries.

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“…This approach was also proposed for the material properties of the cornea. Jannesari et al state that the contribution of material viscosity in the dynamic tonometry test is trivial and can be ignored, but hyper–viscoelastic is a more accurate definition of the behavior of the whole eye globe [ 17 ]. The viscoelastic–hyperelastic model of the cornea is examined in papers [ 18 , 19 ].…”

Section: Introductionmentioning

confidence: 99%

Novel Method of Measuring Corneal Viscoelasticity Using the Corvis ST Tonometer

Boszczyk

Kasprzak

Przeździecka-Dołyk

2022

JCM

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Background: The process of rapid propagation of the corneal deformation in air puff tonometer depends not only on intraocular pressure, but also on the biomechanical properties of the cornea and anterior eye. One of the biomechanical properties of the cornea is viscoelasticity, which is the most visible in its high-speed deformations. It seems reasonable to link the corneal viscoelasticity parameter to two moments of the highest speed of corneal deformations, when the cornea buckles. The aim of this work is to present a method of determining the time and place of occurrence of corneal buckling, examine spatial and temporal dependencies between two corneal applanations and bucklings in the Corvis ST tonometer, and correlate these dependencies with corneal viscoelastic properties. Methods: Images of the horizontal cross section of the Corvis ST deformed cornea from the air puff tonometer Corvis ST were used. 14 volunteers participated in the study, each of them had one eye measured eight times. Mutual changes in the profile slopes of the deformed corneas were numerically determined. They describe pure corneal deformation, eliminating the influence of rotation, and displacement of the entire eyeball. For each point in the central area of the corneal profile, the maximum velocities of mutual slope changes accompanying the applanations were estimated. The times of their occurrence were adopted as buckling times. Results: The propagation of buckling along the corneal profile is presented, as well as the repeatability and mutual correlations between the buckling parameters and intraocular pressure. Based on the relationship between them, a new parameter describing corneal hysteresis: Corvis Viscoelasticity (CVE) is introduced. It is characterized by high repeatability: ICC = 0.82 (0.69–0.93 CI) and low and insignificant correlation with intraocular pressure: r = 0.25 (p-value = 0.38). Conclusion: The results show for the first time how to measure the corneal buckling and viscoelastic effects with Corvis ST. CVE is a new proposed biomechanical parameter related to the viscoelastic properties of the cornea, which has high repeatability for the examined subject. The distribution of its values is planned to be tested on different groups of patients in order to investigate its clinical applicability.

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Numerical and clinical investigation on the material model of the cornea in Corvis tonometry tests: differentiation between hyperelasticity and viscoelasticity

Cited by 14 publications

References 32 publications

The Shape of Corneal Deformation Alters Air Puff–Induced Loading

The Shape of Corneal Deformation Alters Air Puff–Induced Loading

Effects of intracorneal ring segments on the biomechanical response of the ectatic cornea to air-puff: A patient-specific numerical analysis

Novel Method of Measuring Corneal Viscoelasticity Using the Corvis ST Tonometer

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