May 2007
Volume 48, Issue 13
Free
ARVO Annual Meeting Abstract  |   May 2007
Continuum-Level Finite Element Modeling of the Optic Nerve Head: Influence of Microstructure on Biomechanics in Normal and Early Glaucoma Eyes
Author Affiliations & Notes
  • M. D. Roberts
    Discoveries in Sight Research Laboratories, Devers Eye Institute, Portland, Oregon
  • C. F. Burgoyne
    Discoveries in Sight Research Laboratories, Devers Eye Institute, Portland, Oregon
  • R. T. Hart
    Department of Biomedical Engineering, Columbus, Ohio
  • J. C. Downs
    Discoveries in Sight Research Laboratories, Devers Eye Institute, Portland, Oregon
  • Footnotes
    Commercial Relationships M.D. Roberts, None; C.F. Burgoyne, None; R.T. Hart, None; J.C. Downs, None.
  • Footnotes
    Support NIH Grant EY11610
Investigative Ophthalmology & Visual Science May 2007, Vol.48, 3300. doi:
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      M. D. Roberts, C. F. Burgoyne, R. T. Hart, J. C. Downs; Continuum-Level Finite Element Modeling of the Optic Nerve Head: Influence of Microstructure on Biomechanics in Normal and Early Glaucoma Eyes. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3300.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose:: To explore the biomechanical response of the connective tissues of the optic nerve head (ONH) and posterior scleral shell to increased intraocular pressure (IOP) using anatomical 3D finite element (FE) models which incorporate characterization of the porous microstructure of the lamina cribrosa (LC) into the models' material description.

Methods:: Three dimensional reconstructions of the ONH were generated for three pairs of primate eyes, with one eye of each pair exhibiting IOP-induced early glaucoma (EG), using a serial sectioning technique described previously [IOVS, 2004, 45(12)]. Custom software was used to delineate boundaries for the ONH and surrounding peripapillary sclera and segment the 3D LC microstructure [IEEE Trans Med Imag, 2006, 25(3)]. The ONH reconstruction was incorporated into a generic anatomical scleral shell with mapped regional thickness variations [IOVS, 2001, 42(13)] and a FE model was generated.The porous, load-bearing LC was modeled using a continuum approach, with orthotropic material properties for each element in the ONH assigned based on an estimate of the laminar material constant, the connective tissue volume fraction, and the predominant laminar beam orientation measured by the fabric tensor [JBiomech, 1992, 25(1)]. The estimated laminar material constant was adjusted until the average posterior deformation of the anterior ONH surface of the FE model agreed with previously reported deformation data [IOVS, 2003, 44(42)].

Results:: Microstructural characterization showed that in the EG eyes of all pairs, total connective tissue volume increased (67%, 78%, 115% percent increase versus normal).The average volume fraction showed a percentage increase of 11% and 27% in two pairs of eyes. FE analysis of the paired continuum models indicated that the EG eyes required an approximately seven-fold decrease in the laminar modulus to match experimental ONH deformation. Furthermore, inclusion of fabric tensor information engendered an overall stiffening of the ONH structure compared to isotropic material property descriptions.

Conclusions:: While the total amount of connective tissue in the LC region is increased in EG, the FE models show that the material constant is lower in the EG eye of each pair, suggesting that the material properties of the LC connective tissue are compromised. The inclusion of material microstructure (volume fraction and orientation) into FE models has a pronounced effect on biomechanical behavior.

Keywords: lamina cribrosa • computational modeling • intraocular pressure 
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