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Research Papers

Dynamic Response of Intraocular Pressure and Biomechanical Effects of the Eye Considering Fluid-Structure Interaction

[+] Author and Article Information
S. Salimi, S. Simon Park

Department of Mechanical and Manufacturing Engineering,  University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canada

T. Freiheit

Department of Mechanical and Manufacturing Engineering,  University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canadatfreihei@ucalgary.ca

J Biomech Eng 133(9), 091009 (Oct 14, 2011) (11 pages) doi:10.1115/1.4005166 History: Received August 11, 2010; Revised September 19, 2011; Published October 14, 2011

The vibration characteristics of shell structures such as eyes have been shown to vary with intraocular pressure (IOP). Therefore, vibration characteristics of the eye have the potential to provide improved correlation to IOP over traditional IOP measurements. As background to examine an improved IOP correlation, this paper develops a finite element model of an eye subject to vibration. The eye is modeled as a shell structure filled with inviscid pressurized fluid in which there is no mean flow. This model solves a problem of a fluid with coupled structural interactions of a generally spherically shaped shell system. The model is verified by comparing its vibrational characteristics with an experimental modal analysis of an elastic spherical shell filled with water. The structural dynamic effects due to change in pressure of the fluid are examined. It is shown that the frequency response of this fluid-solid coupled system has a clear increase in natural frequency as the fluid pressure rises. The fluid and structure interaction is important for accurate prediction of system dynamics. This model is then extended to improve its accuracy in modeling the eye by including the effect of the lens to study corneal vibration. The effect of biomechanical parameters such as the thicknesses of different parts of the eye and eye dimensions in altering measured natural frequencies is investigated and compared to the influence of biomechanical parameters in Goldmann applanation tonometry models. The dynamic response of the eye is found to be less sensitive to biomechanical parameters than the applanation tonometry model.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Finite element models of elastic spheres. The models are axisymmetric around the vertical axis, 30 degrees of the spheres are shown. (a) Model M1 (b) Model M2 (higher wall density) (c) Model M3

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Figure 2

Comparison of FRFs of Models M1 through M3 at Different Pressures

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Figure 3

EMA set up on the elastic ball (a) schematic (b) impact hammer test

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Figure 4

FRFs Experimental Modal Analysis for Three Internal Pressures

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Figure 5

FRF fitted curve for EMA at 13.7 kPa

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Figure 6

A schematic of profile of the lens [25]

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Figure 7

Complex and simplified lens models load and boundary conditions (cross sectional view) (a) Complex Lens model (for eyewl ) (b) Simplified Lens Model (for eyesl )

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Figure 8

Schematic of the simplified lens FE model (eyesl )

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Figure 9

Comparison eyewl and eyesl Frequency Response Function

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Figure 10

Comparison eyesl and eyenl Frequency Response Function

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Figure 11

FRF of eyesl (simplified lens) at different IOPs

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