The posterior sclera likely plays an important role in the development of glaucoma, and accurate characterization of its mechanical properties is needed to understand its impact on the more delicate optic nerve head—the primary site of damage in the disease. The posterior scleral shells from both eyes of one rhesus monkey were individually mounted on a custom-built pressurization apparatus. Intraocular pressure was incrementally increased from to , and the 3D displacements were measured using electronic speckle pattern interferometry. Finite element meshes of each posterior scleral shell were reconstructed from data generated by a 3D digitizer arm (shape) and a 20 MHz ultrasound transducer (thickness). An anisotropic hyperelastic constitutive model described in a companion paper (Girard, Downs, Burgoyne, and Suh, 2009, “Peripapillary and Posterior Scleral Mechanics—Part I: Development of an Anisotropic Hyperelastic Constitutive Model,” ASME J. Biomech. Eng., 131, p. 051011), which includes stretch-induced stiffening and multidirectional alignment of the collagen fibers, was applied to each reconstructed mesh. Surface node displacements of each model were fitted to the experimental displacements using an inverse finite element method, which estimated a unique set of 13 model parameters. The predictions of the proposed constitutive model matched the 3D experimental displacements well. In both eyes, the tangent modulus increased dramatically with IOP, which indicates that the sclera is mechanically nonlinear. The sclera adjacent to the optic nerve head, known as the peripapillary sclera, was thickest and exhibited the lowest tangent modulus, which might have contributed to the uniform distribution of the structural stiffness for each entire scleral shell. Posterior scleral deformation following acute IOP elevations appears to be nonlinear and governed by the underlying scleral collagen microstructure as predicted by finite element modeling. The method is currently being used to characterize posterior scleral mechanics in normal (young and old), early, and moderately glaucomatous monkey eyes.
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Peripapillary and Posterior Scleral Mechanics—Part II: Experimental and Inverse Finite Element Characterization
Michaël J. A. Girard,
Michaël J. A. Girard
Department of Biomedical Engineering,
e-mail: michael.girard@me.com
Tulane University
, 6823 St. Charles Avenue, New Orleans, LA 70118; Ocular Biomechanics Laboratory, Devers Eye Institute, Legacy Health Research
, 1225 NE 2nd Avenue, Portland, OR 97232
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J. Crawford Downs,
J. Crawford Downs
Ocular Biomechanics Laboratory, Devers Eye Institute,
Legacy Health Research
, 1225 NE 2nd Avenue, Portland, OR 97232; Department of Biomedical Engineering, Tulane University
, 6823 St. Charles Avenue, New Orleans, LA 70118
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Michael Bottlang,
Michael Bottlang
Biomechanics Laboratory,
Legacy Health Research
, 1225 NE 2nd Avenue, Portland, OR 97232
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Claude F. Burgoyne,
Claude F. Burgoyne
Optic Nerve Head Research Laboratory, Devers Eye Institute,
Legacy Health Research
, 1225 NE 2nd Avenue, Portland, OR 97232; Department of Biomedical Engineering, Tulane University
, 6823 St. Charles Avenue, New Orleans, LA 70118
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J.-K. Francis Suh
J.-K. Francis Suh
Moksan BioEng LLC
, 605 Middle Street, Unit No. 25, Braintree, MA 02184; Department of Biomedical Engineering, Tulane University
, 6823 St. Charles Avenue, New Orleans, LA 70118
Search for other works by this author on:
Michaël J. A. Girard
Department of Biomedical Engineering,
Tulane University
, 6823 St. Charles Avenue, New Orleans, LA 70118; Ocular Biomechanics Laboratory, Devers Eye Institute, Legacy Health Research
, 1225 NE 2nd Avenue, Portland, OR 97232e-mail: michael.girard@me.com
J. Crawford Downs
Ocular Biomechanics Laboratory, Devers Eye Institute,
Legacy Health Research
, 1225 NE 2nd Avenue, Portland, OR 97232; Department of Biomedical Engineering, Tulane University
, 6823 St. Charles Avenue, New Orleans, LA 70118
Michael Bottlang
Biomechanics Laboratory,
Legacy Health Research
, 1225 NE 2nd Avenue, Portland, OR 97232
Claude F. Burgoyne
Optic Nerve Head Research Laboratory, Devers Eye Institute,
Legacy Health Research
, 1225 NE 2nd Avenue, Portland, OR 97232; Department of Biomedical Engineering, Tulane University
, 6823 St. Charles Avenue, New Orleans, LA 70118
J.-K. Francis Suh
Moksan BioEng LLC
, 605 Middle Street, Unit No. 25, Braintree, MA 02184; Department of Biomedical Engineering, Tulane University
, 6823 St. Charles Avenue, New Orleans, LA 70118J Biomech Eng. May 2009, 131(5): 051012 (10 pages)
Published Online: April 15, 2009
Article history
Received:
June 21, 2008
Revised:
December 11, 2008
Published:
April 15, 2009
Connected Content
A companion article has been published:
Peripapillary and Posterior Scleral Mechanics—Part I: Development of an Anisotropic Hyperelastic Constitutive Model
Citation
Girard, M. J. A., Downs, J. C., Bottlang, M., Burgoyne, C. F., and Suh, J. F. (April 15, 2009). "Peripapillary and Posterior Scleral Mechanics—Part II: Experimental and Inverse Finite Element Characterization." ASME. J Biomech Eng. May 2009; 131(5): 051012. https://doi.org/10.1115/1.3113683
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