Corneal Biomechanical Properties from Two-Dimensional Corneal Flap Extensiometry: Application to UV-Riboflavin Cross-Linking

Kling, Sabine; Ginis, Harilaos; Marcos, Susana

doi:10.1167/iovs.12-9583

Cited by 31 publications

(19 citation statements)

References 22 publications

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“…Both methods captured the inter-eye differences of the measured samples. On the other hand the reconstructed values are in agreement with previous reports in the literature on porcine corneas: 0.8–2.6 MPa from Wollensak et al using uniaxial extensiometry [37]; 0.6–3.9 MPa from Kling et al, using eye’s inflation [15]. The differences between the measured and simulated results may come from the assumptions of the material models.…”

Section: Discussionsupporting

confidence: 89%

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Material Properties from Air Puff Corneal Deformation by Numerical Simulations on Model Corneas

et al. 2016

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ObjectiveTo validate a new method for reconstructing corneal biomechanical properties from air puff corneal deformation images using hydrogel polymer model corneas and porcine corneas.MethodsAir puff deformation imaging was performed on model eyes with artificial corneas made out of three different hydrogel materials with three different thicknesses and on porcine eyes, at constant intraocular pressure of 15 mmHg. The cornea air puff deformation was modeled using finite elements, and hyperelastic material parameters were determined through inverse modeling, minimizing the difference between the simulated and the measured central deformation amplitude and central-peripheral deformation ratio parameters. Uniaxial tensile tests were performed on the model cornea materials as well as on corneal strips, and the results were compared to stress-strain simulations assuming the reconstructed material parameters.ResultsThe measured and simulated spatial and temporal profiles of the air puff deformation tests were in good agreement (< 7% average discrepancy). The simulated stress-strain curves of the studied hydrogel corneal materials fitted well the experimental stress-strain curves from uniaxial extensiometry, particularly in the 0–0.4 range. Equivalent Young´s moduli of the reconstructed material properties from air-puff were 0.31, 0.58 and 0.48 MPa for the three polymer materials respectively which differed < 1% from those obtained from extensiometry. The simulations of the same material but different thickness resulted in similar reconstructed material properties. The air-puff reconstructed average equivalent Young´s modulus of the porcine corneas was 1.3 MPa, within 18% of that obtained from extensiometry.ConclusionsAir puff corneal deformation imaging with inverse finite element modeling can retrieve material properties of model hydrogel polymer corneas and real corneas, which are in good correspondence with those obtained from uniaxial extensiometry, suggesting that this is a promising technique to retrieve quantitative corneal biomechanical properties.

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Section: Discussionsupporting

confidence: 89%

“…A disadvantage of these tests is that post-mortem time influences the hydration state of the cornea, which in turn affects the mechanical properties [11]. Also, tests requiring the use of corneal strips are affected by the orientation and density of the collagen fibers [12–14], and changes in the boundary conditions [15]. …”

Section: Introductionmentioning

confidence: 99%

Material Properties from Air Puff Corneal Deformation by Numerical Simulations on Model Corneas

et al. 2016

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“…Twodimensional extensometry 30 as applied in this study resembles the natural condition in a more realistic way than onedimensional extensometry, which has been used for the biomechanical analysis of porcine, rabbit, and human corneas. 6,16 We could confirm the finding of a previous study 17 that viscoelastic testing approaches, such as stress-relaxation or creep tests, are more sensitive to measure the effect of CXL.…”

Section: Discussionmentioning

confidence: 99%

Establishing Corneal Cross-Linking With Riboflavin and UV-A in the Mouse Cornea In Vivo: Biomechanical Analysis

Hammer

Kling

Boldi

et al. 2015

Invest. Ophthalmol. Vis. Sci.

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PURPOSE. To establish corneal cross-linking (CXL) with riboflavin and UV-A in in the mouse cornea in vivo and to develop tools to measure the biomechanical changes observed. METHODS.A total of 55 male C57BL/6 wild-type mice (aged 5 weeks) were divided into 14 groups. Standard CXL parameters were adapted to the anatomy of the mouse cornea, and riboflavin concentration (0.1%-0.5%) and fluence series (0.09-5.4 J/cm 2 ) were performed on the assumption of the endothelial damage thresholds. Untreated and riboflavin only corneas were used as controls. Animals were killed at 30 minutes and at 1 month after CXL. Corneas were harvested. Two-dimensional (2D) biomechanical testing was performed using a customized corneal holder in a commercially available stress-strain extensometer/indenter. Both elastic and viscoelastic analyses were performed. Statistical inference was performed using t-tests and specific mathematical models fitted to the experimental stress-strain and stressrelaxation data. Adjusted P values by the method of Benjamini and Hochberg are reported.RESULTS. For all CXL treatment groups, stress-relaxation showed significant differences (P < 0.0001) after 120 seconds of constant strain application, with cross-linked corneas maintaining a higher stress (441 6 40 kPa) when compared with controls (337 6 39 kPa). Stress-strain analysis confirmed these findings but was less sensitive to CXL-induced changes: at 0.5% of strain, cross-linked corneas remained at higher stress (778 6 111 kPa) when compared with controls (659 6 121 kPa).CONCLUSIONS. Cross-linking was induced in the mouse cornea in vivo, and its biomechanical effect successfully measured. This could create opportunities to study molecular pathways of CXL in transgenic mice.

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“…Ex-vivo biomechanical testing methods currently applied to measure corneas include tensile stretching (or strip extensiometry) 7–20 , bulge/inflation testing 18, 21–27 , nanoindentation testing (atomic force microscopy, AFM) 28–35 , indentation testing 36 , shear testing 4, 37 , and acoustic radiation force elastic microscopy 38 . Despite the existence of a variety of characterization methods available, the published values derived from such techniques lack reproducibility, evidenced by the large range of reported corneal Young’s modulus of elasticity values in literature (0.57kPa – 41MPa) 7–18, 21–36, 39 . Although the varied nature of the characterization methods may contribute to the sizable range of published elasticity values, one should not assume that this is the sole reason.…”

Section: Introductionmentioning

confidence: 99%

Impact of Hydration Media on Ex Vivo Corneal Elasticity Measurements

Dias

Ziebarth

2015

Eye &Amp; Contact Lens: Science &Amp; Clinical Practice

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Objectives To determine the effect of hydration media on ex vivo corneal elasticity. Methods Experiments were conducted on forty porcine eyes retrieved from an abattoir (10 eyes each for PBS, BSS, Optisol, 15% Dextran). The epithelium was removed and the cornea was excised with an intact scleral rim and placed in 20% Dextran overnight to restore its physiological thickness. For each hydration media, corneas were evenly divided into two groups: one with an intact scleral rim and the other without. Corneas were mounted onto a custom chamber and immersed in a hydration medium for elasticity testing. While in each medium, corneal elasticity measurements were performed for 2 hours: at 5-minute intervals for the first 30 minutes and then 15-minute intervals for the remaining 90 minutes. Elasticity testing was performed using nanoindentation with spherical indenters and Young’s modulus was calculated using the Hertz model. Thickness measurements were taken before and after elasticity testing. Results The percentage change in corneal thickness and elasticity was calculated for each hydration media group. BSS, PBS, and Optisol showed an increase in thickness and Young’s moduli for corneas with and without an intact scleral rim. 15% Dextran exhibited a dehydrating effect on corneal thickness and provided stable maintenance of corneal elasticity for both groups. Conclusions Hydration media affects the stability of corneal thickness and elasticity measurements over time. 15% Dextran was most effective in maintaining corneal hydration and elasticity, followed by Optisol.

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Corneal Biomechanical Properties from Two-Dimensional Corneal Flap Extensiometry: Application to UV-Riboflavin Cross-Linking

Cited by 31 publications

References 22 publications

Material Properties from Air Puff Corneal Deformation by Numerical Simulations on Model Corneas

Material Properties from Air Puff Corneal Deformation by Numerical Simulations on Model Corneas

Establishing Corneal Cross-Linking With Riboflavin and UV-A in the Mouse Cornea In Vivo: Biomechanical Analysis

Impact of Hydration Media on Ex Vivo Corneal Elasticity Measurements

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