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M. D. Roberts, J. Grimm, J. Reynaud, I. A. Sigal, C. F. Burgoyne, J. C. Downs; Modeling of Optic Nerve Head (ONH) Biomechanics in Bilaterally Normal Monkeys. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4891.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the biomechanical response of 4 pairs of bilaterally normal monkey eyes to IOP elevation using eye-specific 3D finite element models of the ONH which include detailed descriptions of LC microarchitecture.
3D reconstructions of the ONH were generated for 4 pairs of normal monkey eyes and used to construct continuum finite element models of their posterior poles [IOVS, 2004, 45(12); ARVO 2007, #378-B314]. Material properties (stiffness) for each of 45 LC elements were assigned based on the predominant LC beam orientation and connective tissue volume fraction (CTVF) [IOVS, 2008, Sept 20, Epub]. A global LC material constant was used for all eyes. LC elements were regionalized into Superior, Inferior, Nasal, Temporal, and Central zones and strain and stress were calculated for an acute IOP elevation from 10 to 45 mmHg. Average scleral canal expansion at the anterior and posterior laminar insertions (ALI and PLI) and LC displacement were also calculated.
Scleral canal expansion, stress, and strain in contralateral eyes were remarkably similar, but there were large differences between animals (see Table). Regional analysis showed that the highest strains and lowest stresses were associated with areas of lowest CTVF (primarily Temporal) but this did not translate into larger LC displacement in the highly strained regions. Conversely, the highest stresses and lowest strains were associated with regions with the highest CTVF (primarily Central and Superior). Average LC displacement was posterior (0.4 to 13 µm outward) and radial PLI expansion was larger than ALI expansion.
These results confirm that the anatomic similarity in contralateral monkey eyes translates into bilaterally similar mechanical behavior at the macro-scale, despite some differences in local LC microarchitecture. The models predicted an inverse relationship between regional LC CTVF and tensile strain, with the less dense temporal region being subjected to the highest strains and the robust central and superior regions bearing the lowest strains.
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