A numerical-experimental protocol to characterize corneal tissue with an application to predict astigmatic keratotomy surgery

Ariza-Gracia, Miguel Ángel; Ortillés, Ángel; Cristobal, Ja; Matas, José Félix Rodríguez; Calvo, Begoña

doi:10.1016/j.jmbbm.2017.06.017

Cited by 17 publications

(11 citation statements)

References 33 publications

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“…Figure 7 shows the relationship between the corrected D and IOP a under various IOP conditions, with the actual IOP values inside being assumed to be 7.5, 15, 22.5, and 45 mmHg. The curve corresponding to the low IOP value (7.5 mmHg) demonstrates a nearly constant IOP a in these models, indicating the rigidity of the structural system providing a considerably greater opposing force than the force obtained from the actual IOP 14 . By contrast, a high IOP could bend the peripheral cornea outwards and flatten the central cornea, resulting in a low IOP a upon applanation.…”

Section: Resultsmentioning

confidence: 80%

“…Thus, the stress is transferred to the minor axis and increases the values as illustrated in Figure S1c . Upon applanation, the hoop stress, , in the central cornea decreased because the applanation force bent the central cornea inward, thus compressing the top of the central cornea 14 .…”

Section: Resultsmentioning

confidence: 99%

“…reported that the noncontact tonometry test is not sufficient to evaluate the individual mechanical properties and a complete in vivo characterization of the preoperative cornea, in which the anterior cornea presents compression in a range of 0–0.4 MPa individually 13 . Other ex vivo measurements with a numerical-experimental protocol, which include biaxial tension and bending experiments, should be used to calibrate corneal mechanical properties individually 14 , 15 . Furthermore, measuring the entire shape of the cornea 16 , 17 instead of the apical displacements, with an in vivo biomechanical analyser is indispensable for this purpose 18 , because the limbus stiffness is 47.3% lower than that of the central cornea.…”

Section: Introductionmentioning

confidence: 99%

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Biomechanical Simulation of Stress Concentration and Intraocular Pressure in Corneas Subjected to Myopic Refractive Surgical Procedures

Shih

Wang

Cai

et al. 2017

Sci Rep

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Recent advances in the analysis of corneal biomechanical properties remain difficult to predict the structural stability before and after refractive surgery. In this regard, we applied the finite element method (FEM) to determine the roles of the Bowman’s membrane, stroma, and Descemet’s membrane in the hoop stresses of cornea, under tension (physiological) and bending (nonphysiological), for patients who undergo radial keratotomy (RK), photorefractive keratectomy (PRK), laser-assisted in situ keratomileusis (LASIK), or small incision lenticule extraction (SMILE). The stress concentration maps, potential creak zones, and potential errors in intraocular pressure (IOP) measurements were further determined. Our results confirmed that the Bowman’s membrane and Descemet’s membrane accounted for 20% of the bending rigidity of the cornea, and became the force pair dominating the bending behaviour of the cornea, the high stress in the distribution map, and a stretch to avoid structural failure. In addition, PRK broke the central linking of hoop stresses and concentrated stress on the edge of the Bowman’s membrane around ablation, which posed considerable risk of potential creaks. Compared with SMILE, LASIK had a higher risk of developing creaks around the ablation in the stroma layer. Our FEM models also predicted the postoperative IOPs precisely in a conditional manner.

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Section: Resultsmentioning

confidence: 80%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Biomechanical Simulation of Stress Concentration and Intraocular Pressure in Corneas Subjected to Myopic Refractive Surgical Procedures

Shih

Wang

Cai

et al. 2017

Sci Rep

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“…As previously reported [13,21], the material behavior of the cornea was defined by a Demiray strain energy function [22] to account for its nonlinear stress/strain relationship;…”

Section: Geometrical and Mechanical Descriptionmentioning

confidence: 99%

Fluid–structure simulation of a general non-contact tonometry. A required complexity?

Ariza-Gracia

Calvo

et al. 2018

Computer Methods in Applied Mechanics and Engineering

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Understanding corneal biomechanics is important for applications regarding refractive surgery prediction outcomes and the study of pathologies affecting the cornea itself. In this regard, non-contact tonometry (NCT) is gaining interest as a non-invasive diagnostic tool in ophthalmology, and is becoming an alternative method to characterize corneal biomechanics : in :::: vivo. In general, identification of material parameters of the cornea from a NCT test relies on the inverse finite element method, for which an accurate and reliable modelization of the test is required. This study explores four different :::::::: modelling : strategies ranging from pure structural analysis up to a fluid-structure interaction model considering the air-cornea and humour-cornea interactions. The four approaches have been compared using clinical biomarkers commonly used in ophthalmology. Results from the simulations indicate the importance of considering the humors as fluids and the deformation of the cornea when determining the pressure applied by the air-jet during the test. Ignoring this two elements in the modeling lead to an overestimation of corneal displacement and therefore an overestimation of corneal stiffness when using the inverse finite element method.

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“…The wavefront error of the optical system was calculated using an in-house ray tracing algorithm 34 and fitted using Zernike polynomials 35 to calculate the SE, 36

where

(µm) is the Zernike coefficient corresponding to the defocus and r 0 (mm) is the radius of the exit pupil of the optical system.…”

Section: Methodsmentioning

confidence: 99%

Corneal Biomechanics After Intrastromal Ring Surgery: Optomechanical In Silico Assessment

Ariza-Gracia

Flecha-Lescún

Büchler

et al. 2020

Trans. Vis. Sci. Tech.

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Purpose To provide a biomechanical framework to better understand the postsurgical optomechanical behavior of the cornea after ring implantation. Methods Calibrated in silico models were used to determine the corneal shape and stresses after ring implantation. After mechanical simulations, geometric ray-tracing was used to determine the change in spherical equivalent. The effect of the surgical procedure, circadian variation of intraocular pressure, or the biomechanical weakening introduced by keratoconus (KC) were evaluated for each intrastromal ring. Results Models predicted the postsurgical optomechanical response of the cornea at a population level. The localized mechanical effect of the additional intrastromal volume introduced by the implants (size and diameter) drives the postsurgical corneal response. However, central corneal stresses did not increase more than 50%, and thus implants did not strengthen the cornea globally. Because of the biomechanical weakening introduced by laser pocketing, continuous implants in a pocket resulted in higher refractive corrections and in the relaxation of the anterior stroma, which could slow down KC progression. Implants can move within the stroma, acting as a dynamic pivot point that modifies corneal kinematics and flattens the corneal center. Changes in stromal mechanical properties did not impact on refraction for normal or pathological corneas. Conclusions Implants do not stiffen the cornea but create a local bulkening effect that regularizes the corneal shape by modifying corneal kinematics without canceling corneal motion. Translational Relevance In silico models can help to understand corneal biomechanics, to plan patient-specific interventions, or to create biomechanically driven nomograms.

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A numerical-experimental protocol to characterize corneal tissue with an application to predict astigmatic keratotomy surgery

Cited by 17 publications

References 33 publications

Biomechanical Simulation of Stress Concentration and Intraocular Pressure in Corneas Subjected to Myopic Refractive Surgical Procedures

Biomechanical Simulation of Stress Concentration and Intraocular Pressure in Corneas Subjected to Myopic Refractive Surgical Procedures

Fluid–structure simulation of a general non-contact tonometry. A required complexity?

Corneal Biomechanics After Intrastromal Ring Surgery: Optomechanical In Silico Assessment

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