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Benjamin Cruz Perez, Hugh J Morris, Hong Chen, Xueliang Pan, Richard T Hart, Jun Liu; 3D Strains in Porcine Superotemporal Posterior Sclera during Inflation. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4262.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize the 3D strains of the porcine superotemporal posterior sclera during inflation using 3D high-resolution ultrasound speckle tracking.
Six porcine globes were tested within 72 hrs postmortem. The corneoscleral shell was mounted on a custom-made pressurization chamber and preconditioned by five cycles of inflation from 5 to 35 mmHg. After a 30 min equilibration at 15 mmHg, the shell was inflated to 17 mmHg and then 19 mmHg with a 7 min equilibration in between. The specimen was immersed in 0.9% saline solution during the tests. A volume of 5.5 mm long, 2 mm wide, and encompassing the full-thickness of the posterior superotemporal sclera was scanned using a 55-MHz ultrasound probe by stacking 2D scans with a 14 μm interval. 3D speckle tracking, validated in simulated radiofrequency data, was performed in the scanned volume using a modified cross-correlation algorithm (Tang & Liu, J Biomech Eng 2012, 134(9)). The full strain tensor was computed using a 3D least-squares strain estimator. Principal strains and volume ratios were computed. The scanned volume was further divided into two sub-regions of equal length (adjacent to ONH and about 2.5-mm away from ONH). The strains and volume ratios of these two regions were compared using paired t-tests.
The principal strains and volume ratios for the overall scanned volume and the two sub-regions are summarized in Table 1. The region close to the ONH showed significantly larger compressive strains than the region farther from the ONH (p<0.001). In addition, as the pressure increased, the volume ratio decreased in the region close to the ONH (p=0.001) while increased in the region farther away (p=0.029).
Ultrasound speckle tracking was successfully implemented to measure the 3D deformation of the posterior sclera during inflation. Initial results suggested substantial negative strains (ε1) during IOP increase presumably due to radial compression. The regions immediately adjacent to the ONH appeared to have larger strains than the regions farther away from ONH. This technique may provide more complete experimental characterization of the posterior sclera and benefit the computational modeling efforts to elucidate the role of sclera in optic nerve damage.
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