March 2012
Volume 53, Issue 14
Free
ARVO Annual Meeting Abstract  |   March 2012
Regional Variations in Mechanical Strain in the Posterior Human Sclera
Author Affiliations & Notes
  • Massimo A. Fazio
    Ocular Biomechanics Laboratory, Devers Eye Institute, Portland, Oregon
  • Rafael Grytz
    Ocular Biomechanics Laboratory, Devers Eye Institute, Portland, Oregon
  • Luigi Bruno
    Mechanical Engineering, University of Calabria, Cosenza, Italy
  • Michael J. Girard
    Bioengineering, Imperial College London, London, United Kingdom
  • Christopher A. Girkin
    Ophthalmology, Univ of Alabama at Birmingham, Birmingham, Alabama
  • Andrea Poggialini
    Mechanical Engineering, University of Calabria, Cosenza, Italy
  • Crawford Downs
    Ocular Biomechanics Laboratory, Devers Eye Institute, Portland, Oregon
  • Footnotes
    Commercial Relationships  Massimo A. Fazio, None; Rafael Grytz, None; Luigi Bruno, None; Michael J. Girard, None; Christopher A. Girkin, None; Andrea Poggialini, None; Crawford Downs, None
  • Footnotes
    Support  NIH Grants R01-EY18926, R01-EY19333; Legacy Good Samaritan Foundation
Investigative Ophthalmology & Visual Science March 2012, Vol.53, 3188. doi:
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      Massimo A. Fazio, Rafael Grytz, Luigi Bruno, Michael J. Girard, Christopher A. Girkin, Andrea Poggialini, Crawford Downs; Regional Variations in Mechanical Strain in the Posterior Human Sclera. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3188.

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

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Abstract
 
Purpose:
 

To establish regional variability of the mechanical behavior of peripapillary and mid-peripheral sclera in normal eyes of elderly human donors.

 
Methods:
 

Ten pairs of normal eyes from human donors aged 57 to 90 years old were mechanically inflation tested within 48 hours post mortem as follows. The intact posterior scleral shell of each eye was pressurized from 5 to 45 mmHg while the full-field three-dimensional displacements of the scleral surface were measured using laser speckle interferometry. A customized B-spline system was used to fit the displacement field to continuous and differentiable analytical functions, from which the full strain tensor of the outer sclera surface was calculated assuming tissue incompressibility. Mean maximum principal (tensile) strain was computed overall and for eight circumferential sectors (45° wide) within the peripapillary and mid-peripheral regions surrounding the optic nerve head (ONH). The peripapillary region was defined as a ~9 degree-wide-band adjacent to the ONH and the mid-peripheral region as a ~6 degree-wide-band immediately outside the peripapillary region.

 
Results:
 

On average, the peripapillary sclera exhibited significantly higher tensile strain (1.2%) than mid-peripheral sclera (0.95%) for a 40 mmHg IOP elevation (p<0.001). Regional differences are presented in the Figure. In the peripapillary region, the inferior sector exhibited the highest tensile strain (1.35%) while the superotemporal had the lowest strain (1.12%). In the mid-peripheral region, the temporal sector had the highest tensile strain (1.07%) while the superonasal sector exhibited the lowest (0.86%).

 
Conclusions:
 

Human posterior sclera exhibits highly complex mechanical behavior in response to acute IOP elevations from 5 to 45 mmHg. These results indicate 1) the peripapillary sclera is subjected to significantly higher tensile strain than the midperipheral sclera, and 2) there is a tendency for strain to concentrate inferiorly in the peripapillary sclera, which could contribute to the increased susceptibility of focal glaucomatous damage seen in the inferior ONH.  

 
Keywords: sclera • stress response • optic nerve 
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