April 2014
Volume 55, Issue 13
Free
ARVO Annual Meeting Abstract  |   April 2014
Age and Racial Differences in Mechanical Energy Absorption in the Posterior Human Sclera
Author Affiliations & Notes
  • Massimo Antonio Fazio
    Ophthalmology, School of Medicine, The University of Alabama at Birmingham, Birmingham, AL
  • Jeffrey S Morris
    Biostatistics, The University of Texas MD Anderson Cancer Center, Houston, TX
  • Rafael Grytz
    Ophthalmology, School of Medicine, The University of Alabama at Birmingham, Birmingham, AL
  • Luigi Bruno
    Mechanical Engineering, University of Calabria, Arcavacata di Rende, Italy
  • Christopher A Girkin
    Ophthalmology, School of Medicine, The University of Alabama at Birmingham, Birmingham, AL
  • J Crawford C Downs
    Ophthalmology, School of Medicine, The University of Alabama at Birmingham, Birmingham, AL
  • Footnotes
    Commercial Relationships Massimo Fazio, None; Jeffrey Morris, None; Rafael Grytz, None; Luigi Bruno, None; Christopher Girkin, None; J Crawford Downs, None
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science April 2014, Vol.55, 4552. doi:
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      Massimo Antonio Fazio, Jeffrey S Morris, Rafael Grytz, Luigi Bruno, Christopher A Girkin, J Crawford C Downs; Age and Racial Differences in Mechanical Energy Absorption in the Posterior Human Sclera. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4552.

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

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Abstract
 
Purpose
 

To establish the age and racial differences in the peripapillary human sclera’s capability to absorb mechanical energy from IOP-induced deformation in normal donors of African (AD) and European (ED) descent.

 
Methods
 

Twenty-eight pairs of normal eyes from human donors (9 AD, 19 ED) aged 20 to 90 years were inflation tested within 48 hours post mortem. The intact posterior scleral shell of each eye was pressurized while the full-field, three-dimensional displacements of the outer scleral surface were measured using laser speckle interferometry (ESPI). By analytical differentiation of the displacement field, the mean maximum principal (tensile) strain was computed at 10 pressure levels from 5 to 45 mmHg within the ~2-mm-wide band of peripapillary sclera surrounding the optic nerve head. An asymptotic functional form (strain = a + b*IOP + IOP/c) was used to fit the variation of strain at the increasing IOP (Figure; R2=0.99). The area under the strain-IOP curve, representing the total mechanical energy absorbed by the peripapillary sclera was computed by analytical integration.

 
Results
 

In both the AD and ED groups, the ability of the peripapillary sclera to absorb IOP-induced deformation decreased significantly with age (p<0.001, Figure), and was more pronounced in the AD group (p<0.05).

 
Conclusions
 

These results indicate 1) with advancing age, the peripapillary sclera suffers a significant loss in its ability to absorb mechanical energy from IOP-induced deformations. 2) AD eyes showed a significantly more rapid decline with age than ED eyes. These racial differences may increase the magnitude of transient IOP elevations and thereby contribute to the increased susceptibility of the elderly and persons of AD to glaucoma.

 
 
Figure (Top): strain-IOP response of the peripapillary sclera for 3 representative pairs of human eyes. Experimentally-derived maximum principal strain at 10 pressure levels (green dots) was fit to an asymptotic function (grey curves). The area under the curve (AUC, yellow) represents the IOP-induced ability of the peripapillary sclera to absorb mechanical energy per unit tissue volume. (Bottom): AUC values for the ED (blue) and AD (red) groups and of the predicted means for increasing age. The sclera’s capability to absorb IOP-induced deformations decreased with age in both the ED (p<0.001), and AD groups (p<0.001). The rate of change with age was more pronounced in the AD group (p<0.05)
 
Figure (Top): strain-IOP response of the peripapillary sclera for 3 representative pairs of human eyes. Experimentally-derived maximum principal strain at 10 pressure levels (green dots) was fit to an asymptotic function (grey curves). The area under the curve (AUC, yellow) represents the IOP-induced ability of the peripapillary sclera to absorb mechanical energy per unit tissue volume. (Bottom): AUC values for the ED (blue) and AD (red) groups and of the predicted means for increasing age. The sclera’s capability to absorb IOP-induced deformations decreased with age in both the ED (p<0.001), and AD groups (p<0.001). The rate of change with age was more pronounced in the AD group (p<0.05)
 
Keywords: 708 sclera • 413 aging  
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