A Multi-Scale Model for the Mechanics of the Human Lens Capsule Harvey Burd Civil Engineering...
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A Multi-Scale Model for the Mechanics of the Human Lens Capsule Harvey Burd Civil Engineering Research Group Department of Engineering Science, Oxford University, UK Finite element model Schematic eye capsule
A Multi-Scale Model for the Mechanics of the Human Lens Capsule Harvey Burd Civil Engineering Research Group Department of Engineering Science, Oxford
A Multi-Scale Model for the Mechanics of the Human Lens Capsule
Harvey Burd Civil Engineering Research Group Department of
Engineering Science, Oxford University, UK Finite element model
Schematic eye capsule
Slide 2
Scope Background Accommodation mechanism Finite element
analysis of the human lens Mechanics of the lens capsule Uniaxial
and biaxial test data. Structural constitutive model (Micronet) 1
Multi-scale finite element analysis Implementation of the Micronet
model in an axisymmetric hyperelastic finite element program
Example analyses 1. Burd (2009) Biomech Model Mechanobiol 8(3)
217-231
Slide 3
Anatomy of the human eye Aqueous Vitreous Ciliary body
Zonules
Slide 4
Accommodation (Helmholtz 1909) Zonule Ciliary body Iris Cornea
AccommodatedUnaccommodated
Slide 5
Lens : geometric model ref. Wolffs Anatomy Axis of symmetry
Lens outline MRI data on 29 and 45 year lenses. Hermans et al. 2008
Zonule geometry: Age-related model for the geometry of the
intersection of zonules with capsule. Canals et al. 1996;
Farnsworth and Shyne 1979 Ciliary body radius: MRI data. Strenk et
al. 1999 Nucleus outline Brown, 1973; Dubbelman et al., 2003;
Hermans et al., 2007; Kasthurirangan et al., 2008; Sweeney and
Truscott, 1998; Ayaki et al., 1993; Gullapalli et al., 1995
Slide 6
Lens capsule: geometric model
http://www.kumc.edu/instruction/medicine/anatomy/h
istoweb/eye_ear/eye_ear.htm 250 Microns Capsule Lens Data from:
Barraquer et al. (2006). Human lens capsule thickness as a function
of age and location along the sagittal lens perimeter. IOVS Capsule
thickness Anterior pole Posterior pole
Slide 7
(a) Uniaxial Test (Krag et al. 2003) Sample cut from lens
capsule Stress MPa Strain % Mechanics of the lens capsule
Slide 8
(b) Biaxial tests (i) Isolated capsule inflation test (Fisher
1969) Initial capsule geometry P
Slide 9
(ii) In-situ capsule inflation (Pedrigi et al. 2007)
Slide 10
uniaxial test biaxial test Linear elastic model; data on Youngs
modulus
Slide 11
A structural model for the lens capsule (a) Structure of the
lens capsule Barnard et al. 1992 50 nm Filaments of collagen type
IV Barnard et al. 1992 J. Struct. Biol.
Slide 12
(b) Components of a structural model Non-linear pin-jointed
bars ( 2 parameters) Neo-Hookean matrix ( 1 parameter) after
Barnard et al. 1992
Slide 13
(b) Components of a structural model (i) Strain energy density
( ii) Neo-Hookean model for matrix networkmatrix a1a1 a2a2
Slide 14
(b) Components of a structural model (iii) Strain energy
density for bars where
Slide 15
Implementation in multi-scale finite element model a1a1 a2a2
internal bars edge bars Specify stretch ratios 1 and 2 Apply
periodic boundary conditions Constrain one joint to be fixed
Compute updated joint coordinates ( W=0) Compute derivatives
Initial configuration
Slide 16
Generating the internal mesh
Slide 17
Calibration tests Membrane traction = (a) Uniaxial test (b)
Biaxial test Membrane traction =
Slide 18
Simulation of isolated capsule inflation test Fisher
(1969)
Slide 19
Simulation of in-situ capsule inflation test Pedrigi et al.
(2007)
Slide 20
Simulation of in-situ capsule inflation test Pedrigi et al.
(2007)
Slide 21
Simulation of in-situ capsule inflation test circumferential
meridional Point D Point X
Slide 22
Simulation of in-situ capsule inflation test Point D Point
F
Slide 23
Conclusions 3-parameter structural model for the lens capsule
Implementation in axisymmetric finite element analysis Comparison
with previous capsule inflation data
