Combined Use of Parallel-Plate Compression and Finite Element Modeling to Analyze the Mechanical Properties of Intact Porcine Lens

Abstract

The objective of this study is to explore the feasibility of a compression test for measuring mechanical properties of intact eye lenses using novel parallel plate compression equipment to compare the accuracy of implementing a classical Hertzian model and a newly proposed adjusted Hertzian model to calculate Young’s modulus from compression test results using finite element (FE) analysis. Parallel-plate compression tests were performed on porcine lenses. An axisymmetric FE model was developed to simulate the experimental process to evaluate the accuracy of using the classical Hertzian theory of contact mechanics as well as a newly proposed adjusted Hertzian theory model for calculating the equivalent Young’s modulus. By fitting the force-displacement relation obtained from FE simulations to both the classical and adjusted Hertzian theory model and comparing the calculated modulus to the input modulus of the FE model, the results demonstrated that the classical Hertzian theory model overestimated the Young’s modulus with a proportional error of over 10%. The adjusted Hertzian theory model produced results that are closer to original input values with error ratios all lower than 1.29%. Measurements of three porcine lenses from the parallel plate compression experiments were analyzed with resulting values of Young’s modulus of between 3.2[Formula: see text]kPa and 4.3[Formula: see text]kPa calculated. This study demonstrates that the adjusted Hertzian theory of contact mechanics can be applied in conjunction with the parallel-plate compression system to investigate the overall mechanical behavior of intact lenses.

Multimodal quantitative optical elastography of the crystalline lens with optical coherence elastography and Brillouin microscopy

“…Currently, assessing the biomechanical properties of the lens is a challenge due to its location inside the eye-globe. Mechanical loading, which is the gold standard for assessing material properties such as Young's modulus, has been utilized for elasticity estimation of the whole lens [8,9]. However, the lens must be removed from the eye-globe, which limits the applicability of mechanical testing for in vivo measurements.…”

Functional effects of the spatial-varying lens mechanical properties in accommodation

“…There is also a likely underestimation of the elastic modulus in the larger lens biopsy punches and whole lenses due to ellipsoidal geometry potentially dominating instead of cylindrical geometry. This can be partially mitigated by allowing flat plate contact before starting the compression test, but corrections may be better using Hertzian contact theory, and has been demonstrated by other researchers [ 52 ]. It was observed that for biopsy punches below 8 mm the stress–strain curves resembled shapes consistent with linear elastic models rather than Hertzian contact.…”

Design of an Automatically Controlled Multi-Axis Stretching Device for Mechanical Evaluations of the Anterior Eye Segment

“…These include the seminal work by Fisher [25], who developed the spinning lens method to mimic the lens shape change during accommodation using centrifugal forces. A similar technique was investigated by Burd et al [18], the classical compressional method adopted to characterise the overall lens stiffness [26], stretching of the lens to simulate ciliary muscle forces [27] as well as the indentation [28] and oscillational shear rheometry used on sectioned lens samples [12,13,29]. However, the results revealed by studies adopting the above methods have varied over several orders of magnitude in elastic moduli and inconsistencies in the ageing trends have also been reported [2].…”