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Massimo Fazio, Rafael Grytz, Luigi Bruno, Jeffry Morris, Christopher Girkin, J Crawford Downs; Racial Differences in Mechanical Strain in the Posterior Human Sclera. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3156.
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To establish racial differences in the mechanical behavior of peripapillary and mid-peripheral human sclera in normal eyes from donors of African (AD) and European (ED) descent.
Twenty-nine pairs of normal eyes from human donors (9 AD, 20 ED) aged 0 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. Under the assumption of tissue incompressibility, mean maximum principal (tensile) strain was computed within the peripapillary and mid-peripheral regions surrounding the optic nerve head (ONH). The peripapillary and mid-peripheral regions were defined as a ~9 degree-wide-band adjacent to the ONH and the band of equal surface area immediately outside the peripapillary region, respectively.
The posterior sclera stiffened significantly faster with age in both regions of the AD eyes compared to ED donors (Figure; p<0.01). The sclera in both regions stiffened significantly with age in the AD eyes, while only peripapillary region stiffened significantly with age in the ED eyes (p<0.001).
These results indicate 1) the peripapillary sclera is subjected to significantly higher tensile strain than the mid-peripheral sclera, independent of race, 2) AD eyes showed a more rapid stiffening with age than ED eyes, and 3) while the mid-peripheral region doesn't significantly stiffen with age in the ED eyes, a rapid and significant stiffening of the mid-peripheral sclera is present in the AD eyes. These significant racial differences in scleral biomechanics may contribute to the increased susceptibility of AD persons to glaucoma.
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