June 2013
Volume 54, Issue 15
Free
ARVO Annual Meeting Abstract  |   June 2013
Racial Differences in Human Scleral Material Properties
Author Affiliations & Notes
  • Rafael Grytz
    Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, AL
    Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, AL
  • Massimo Fazio
    Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, AL
  • Vincent Libertiaux
    Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, AL
  • Luigi Bruno
    Department of Mechanical Engineering, University of Calabria, Calabria, Italy
  • Stuart Gardiner
    Devers Eye Institute, Portland, OR
  • Christopher Girkin
    Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, AL
  • J Crawford Downs
    Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, AL
    Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, AL
  • Footnotes
    Commercial Relationships Rafael Grytz, None; Massimo Fazio, None; Vincent Libertiaux, None; Luigi Bruno, None; Stuart Gardiner, Allergan (R); Christopher Girkin, SOLX (F), Heidelberg Engineering (F); J Crawford Downs, None
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science June 2013, Vol.54, 79. doi:
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    • Get Citation

      Rafael Grytz, Massimo Fazio, Vincent Libertiaux, Luigi Bruno, Stuart Gardiner, Christopher Girkin, J Crawford Downs; Racial Differences in Human Scleral Material Properties. Invest. Ophthalmol. Vis. Sci. 2013;54(15):79.

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Abstract
 
Purpose
 

To determine the racial differences in the material properties of posterior scleral shells from human donors of European (n=20 eyes) and African (n=11 eyes) descent.

 
Methods
 

Posterior scleral shells were subjected to IOP elevations from 5 to 45 mmHg and the resulting full-field displacements were recorded using laser speckle interferometry. Eye-specific finite element models were generated based on experimentally measured scleral shell surface geometry and thickness. Inverse numerical analyses were performed to identify material parameters for each eye by matching experimental deformation measurements to model predictions using a microstructure-based constitutive formulation that incorporates the crimp response and anisotropic architecture of scleral collagen fibrils. Generalized Estimating Equation models were constructed to determine whether there was a significant effect of race on the fitted material parameters while accounting for age and intra-donor correlations.

 
Results
 

The age-dependent scleral shear modulus is significantly higher (p=0.019) and the collagen fibril crimp angle is lower in donors from African descent, although this did not reach conventional statistical significance (p=0.057, Fig. 1). The IOP-dependent in-plane strains in the peripapillary sclera are significantly lower in donors from African descent (p<0.015 for all IOP levels, Fig. 2).

 
Conclusions
 

Results show that posterior sclera of donors of African descent are stiffer compared to donors of European descent due to both a higher shear stiffness of the nonfibrillar matrix and a lower level of stretch at which the collagen fibrils uncrimp and stiffen. These differences may be due to a higher collagen cross-linking density in donors of African descent and relate to a higher susceptibility to glaucoma.

 
 
Fig. 2. In-plane strain in the peripapillary sclera versus IOP (mean, standard deviation) showing significantly smaller strains in donors from African descent (p<0.015). The lower compliance of the peripapillary sclera in donors of African descent is mainly due to a higher shear modulus and a lower crimp angle of collagen fibrils.
 
Fig. 2. In-plane strain in the peripapillary sclera versus IOP (mean, standard deviation) showing significantly smaller strains in donors from African descent (p<0.015). The lower compliance of the peripapillary sclera in donors of African descent is mainly due to a higher shear modulus and a lower crimp angle of collagen fibrils.
 
 
Fig. 1. Top: Fitted shear moduli versus age showing a significantly higher shear modulus in donors of African descent (p=0.019). Bottom: Fitted crimp angle of collagen fibrils versus age showing evidence for a lower crimp angle in donors of African descent (p=0.057).
 
Fig. 1. Top: Fitted shear moduli versus age showing a significantly higher shear modulus in donors of African descent (p=0.019). Bottom: Fitted crimp angle of collagen fibrils versus age showing evidence for a lower crimp angle in donors of African descent (p=0.057).
 
Keywords: 708 sclera • 473 computational modeling • 413 aging  
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