Inverse elastographic method for analyzing the ocular lens compression test

Reilly, Matthew A.; Cleaver, Andre

doi:10.1142/s1793545817420093

Cited by 8 publications

(6 citation statements)

References 45 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The mechanical nonlinearity of the human capsule turned more significant with a high strain regime [1,3,39], where hyper-elastic models became more appropriate [15,24,42]. More complex behaviours of the biological capsules, such as stress softening, viscoelasticity (creep, relaxation) and anisotropy, exist at different loading conditions [1,[43][44][45][46][47][48][49]. The stress softening, i.e., Mullins effect, was observed for silicone rubber under cyclic loading, and was more evident at higher strain levels [36,50].…”

Section: Discussionmentioning

confidence: 99%

Characterisation and Modelling of an Artificial Lens Capsule Mimicking Accommodation of Human Eyes

Wei

Wolffsohn

Oliveira³

et al. 2021

Polymers

View full text Add to dashboard Cite

A synthetic material of silicone rubber was used to construct an artificial lens capsule (ALC) in order to replicate the biomechanical behaviour of human lens capsule. The silicone rubber was characterised by monotonic and cyclic mechanical tests to reveal its hyper-elastic behaviour under uniaxial tension and simple shear as well as the rate independence. A hyper-elastic constitutive model was calibrated by the testing data and incorporated into finite element analysis (FEA). An experimental setup to simulate eye focusing (accommodation) of ALC was performed to validate the FEA model by evaluating the shape change and reaction force. The characterisation and modelling approach provided an insight into the intrinsic behaviour of materials, addressing the inflating pressure and effective stretch of ALC under the focusing process. The proposed methodology offers a virtual testing environment mimicking human capsules for the variability of dimension and stiffness, which will facilitate the verification of new ophthalmic prototype such as accommodating intraocular lenses (AIOLs).

show abstract

Section: Discussionmentioning

confidence: 99%

Characterisation and Modelling of an Artificial Lens Capsule Mimicking Accommodation of Human Eyes

Wei

Wolffsohn

Oliveira³

et al. 2021

Polymers

View full text Add to dashboard Cite

show abstract

“…The lens can be described as a visco-hyperelastic material consisting of the nucleus, cortex and capsule. The importance of accounting for the lens capsule has recently been demonstrated in a simulation study (Reilly and Cleaver, 2017) under a similar compressive loading. Therefore, following the approach of our recent study (Cabeza-Gil et al, 2023), the lens capsule was modeled with a homogeneous thickness of 60 μm and a Neo-Hookean coefficient of 0.166 MPa (equivalent to a Young's modulus of 1 MPa).…”

Section: Finite Element Modelingmentioning

confidence: 99%

Storage-induced mechanical changes of porcine lenses assessed with optical coherence elastography and inverse finite element modeling

Tahsini,

Gil,

Kling

2024

Front. Bioeng. Biotechnol.

View full text Add to dashboard Cite

IntroductionIn an effort of gaining a better understanding of the lens mechanics, ex vivo lenses samples are often used. Yet, ex vivo tissue might undergo important postmortem changes depending on the unavoidable preservation method employed. The purpose of this study was to assess how various storage conditions and the removal of the lens capsule affect the mechanical properties of ex vivo porcine lens samples.MethodsA total of 81 freshly enucleated porcine eyes were obtained and divided into six groups and preserved differently. In the first three groups, the lens within the intact eye was preserved for 24 h by: (i) freezing at −80°C (n = 12), (ii) freezing at −20°C (n = 12), and (iii) refrigeration at +8°C (n = 12). In the remaining groups, the lenses were immediately extracted and treated as follows: (iv) kept intact, no storage (n = 12), (v) decapsulated, no storage (n = 21), and (vi) immersed in Minimum Essential Medium (MEM) at +8°C (n = 12) for 24 h. Frozen lenses were thawed at room temperature. Each lens was compressed between two glass lamella and subjected, first to a period of relaxation during which the compression force was recorded and second to an oscillating micro-compression while the deformation was recorded with a total of 256 subsequent B-scans via optical coherence tomography. The corresponding axial strain was retrieved via phase-sensitive image processing and subsequently used as input for an inverse finite element analysis (iFEA) to retrieve the visco-hyperelastic material properties of the lenses.ResultsAfter freezing at temperatures of −80°C and −20°C, the cortical strains increased by 14% (p = 0.01) and 34% (p < 0.001), and the nuclear strains decreased by 17% (p = 0.014) and 36% (p < 0.001), compared to the lenses tested immediately after postmortem, respectively. According to iFEA, this resulted from an increased ratio of the nuclear: cortical E-modulus (4.06 and 7.06) in −80°C and −20°C frozen lenses compared to fresh lenses (3.3). Decapsulation had the largest effect on the material constant C10, showing an increase both in the nucleus and cortex. Preservation of the intact eye in the refrigerator induced the least mechanical alterations in the lens, compared to the intact fresh condition.DiscussionCombining iFEA with optical coherence elastography allowed us to identify important changes in the lens mechanics induced after different preserving ex vivo methods.

show abstract

“…The spinning lens test is advantageous as the lens is subject to minor mechanical disturbances during measurement, but internal stiffness variations cannot be determined directly but rather inferred from axisymmetric finite element (FE) inverse analysis using a neo-Hookean model ( Burd et al, 2011 ). Reilly et al implemented the inverse FE method to perform mechanical analysis of both the lens and its capsule from a compression test ( Reilly and Cleaver, 2017 ). This method is promising in enabling the assessement of lenses with different shapes, sizes, and mechanical properties, but the assumed model neglects viscous effects and known spatial variations of lenticular biomechanical properties.…”

Section: Introductionmentioning

confidence: 99%

The lens capsule significantly affects the viscoelastic properties of the lens as quantified by optical coherence elastography

Mekonnen

Zevallos-Delgado²,

Zhang³

et al. 2023

Front. Bioeng. Biotechnol.

View full text Add to dashboard Cite

The crystalline lens is a transparent, biconvex structure that has its curvature and refractive power modulated to focus light onto the retina. This intrinsic morphological adjustment of the lens to fulfill changing visual demands is achieved by the coordinated interaction between the lens and its suspension system, which includes the lens capsule. Thus, characterizing the influence of the lens capsule on the whole lens’s biomechanical properties is important for understanding the physiological process of accommodation and early diagnosis and treatment of lenticular diseases. In this study, we assessed the viscoelastic properties of the lens using phase-sensitive optical coherence elastography (PhS-OCE) coupled with acoustic radiation force (ARF) excitation. The elastic wave propagation induced by ARF excitation, which was focused on the surface of the lens, was tracked with phase-sensitive optical coherence tomography. Experiments were conducted on eight freshly excised porcine lenses before and after the capsular bag was dissected away. Results showed that the group velocity of the surface elastic wave, V, in the lens with the capsule intact (V=2.55±0.23 m/s) was significantly higher (p < 0.001) than after the capsule was removed (V=1.19±0.25 m/s). Similarly, the viscoelastic assessment using a model that utilizes the dispersion of a surface wave showed that both Young’s modulus, E, and shear viscosity coefficient, η, of the encapsulated lens (E=8.14±1.10 kPa,η=0.89±0.093 Pa∙s) were significantly higher than that of the decapsulated lens (E=3.10±0.43 kPa,η=0.28±0.021 Pa∙s). These findings, together with the geometrical change upon removal of the capsule, indicate that the capsule plays a critical role in determining the viscoelastic properties of the crystalline lens.

show abstract

Inverse elastographic method for analyzing the ocular lens compression test

Cited by 8 publications

References 45 publications

Characterisation and Modelling of an Artificial Lens Capsule Mimicking Accommodation of Human Eyes

Characterisation and Modelling of an Artificial Lens Capsule Mimicking Accommodation of Human Eyes

Storage-induced mechanical changes of porcine lenses assessed with optical coherence elastography and inverse finite element modeling

The lens capsule significantly affects the viscoelastic properties of the lens as quantified by optical coherence elastography

Contact Info

Product

Resources

About