The impact of horizontal eye movements versus intraocular pressure on optic nerve head biomechanics: A tridimensional finite element analysis study

Biomechanical simulations of crystalline lens oscillations resulting from the changes in the gaze in an accommodated eye

Purpose

The goal of the study is to introduce a generic, versatile biomechanical model that aims to reproduce the dynamic wobbling phenomenon.

Methods

A systematic strategy is used, which includes a) capturing the in vivo data on a group of healthy volunteers, b) analyzing the changes in Purkinje images over time, and c) performing the combined biomechanical and optical simulations to develop the model that might be useful for understanding the mechanical behavior of the lens during wobbling and its influence on ocular dynamics.

Results

Examples of lens wobbling patterns for six measured eyes were presented, and parameters characterizing the oscillatory motion were determined, including frequency of oscillations, Q-factor, damping factor and time constant. The average values of these parameters are the following: frequency: 20.0 ± 2.4 Hz; Q-factor: 1.86 ± 0.44; damping factor: 0.27 ± 0.06; time constant: 0.11 ± 0.06 s. The data reproduced by means of simulations: frequency: 19.3 Hz; Q-factor: 2.17; damping factor: 0.23; time constant: 0.15 s. This comparison reveals a good agreement between the measured and reconstructed data with the values being within the standard deviation limits.

Conclusion

The developed generic model together with the presented methodology is able to reconstruct the typical crystalline lens wobbling dynamics with a satisfying accuracy. However, the observed intersubject variability highlights the need for personalized biomechanical models. The introduced model may constitute the basis for future individualization of the data, bringing broad perspectives for prospective investigations aimed to explain the biomechanical mechanisms within the eye.

Investigation of crystalline lens overshooting: ex vivo experiment and optomechanical simulation results

Introduction: Crystalline lens overshooting refers to a situation in which the lens momentarily shifts too much from its typical location immediately after stopping the rotational movement of the eye globe. This movement can be observed using an optical technique called Purkinje imaging. Methods: In this work, an experimental setup was designed to reproduce this effect ex vivo using a fresh porcine eye. The sample was rotated 90° around its centroid using a high-velocity rotation stage, and the Purkinje image sequences were recorded, allowing us to quantify the overshooting effect. The numerical part of the study consisted of developing a computational model of the eye, based on the finite element method, that allowed us to understand the biomechanical behavior of the different tissues in this dynamic scenario. A 2D fluid-structure interaction model of the porcine eye globe, considering both the solid parts and humors, was created to reproduce the experimental outcomes. Results: Outputs of the simulation were analyzed using an optical simulation software package to assess whether the mechanical model behaves optically like the real ex vivo eye. The simulation predicted the experimental results by carefully adjusting the mechanical properties of the zonular fibers and the damping factor. Conclusion: This study effectively demonstrates the importance of characterizing the dynamic mechanical properties of the eye tissues to properly comprehend and predict the overshooting effect.