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Hugh Morris, Benjamin Cruz Perez, Junhua Tang, Xueliang Pan, Richard Hart, Paul Weber, Jun Liu; Correlation of Posterior Scleral Strains with IOP Increase by Volume Controlled Infusion. Invest. Ophthalmol. Vis. Sci. 2013;54(15):71.
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© ARVO (1962-2015); The Authors (2016-present)
Corneoscleral biomechanics may be important modulators of dynamic intraocular pressure (IOP). This study tested the hypothesis that IOP increase, induced by controlled increase in intraocular volume, is correlated with the biomechanical responses of the posterior sclera.
Eight porcine globes were tested with 24hrs postmortem. The globes were first perfused with PBS at a constant pressure of 15mmHg and then infused at a rate of 15μL/s for one second using a syringe pump (UltraPhD, Havard Apparatus) to induce an IOP increase. IOP was monitored at a sampling rate of 20Hz using a pressure sensor (TAM-A, Havard Apparatus) and the maximal increase in IOP (ΔIOP) during the infusion was recorded. The sclera shells were then prepared and clamped on a custom-built chamber for inflation testing. The strains along the circumferential and meridian directions on the temporal superior region of the posterior sclera, induced by inflation of the sclera shell from 5 to 45 mmHg, were measured by ultrasound speckle tracking (Tang & Liu, J. Biomech Eng 2012, 134(9)). The relationships between the sclera strains and ΔIOP were evaluated using Pearson correlation coefficients.
ΔIOP was 10.9 ± 2.4 mmHg at a 15 μl volume infusion. Along the circumferential direction, the axial strains in the posterior sclera were -1.0 ± -0.3%, -2.1 ± -0.6%, -2.7 ± -0.8%, and -3.4 ± -1.0%, and the lateral strains were 0.7 ± 0.3%, 1.2 ± 0.5%, 1.4 ± 0.5%, and 1.6 ± 0.6%, at pressures of 10, 20, 30, and 45 mmHg. Correlation coefficients between ΔIOP and circumferential axial strains ranged from 0.73 and 0.79 for inflation pressures from 10 to 45 mmHg (all p<0.05). Correlation coefficients between ΔIOP and circumferential lateral strains were -0.57 to -0.73 at different inflation pressures (p-values ranged from 0.039 to 0.139). Similar correlations were observed in the meridian strains, but the p-values were generally larger.
This study showed lower axial compression and smaller lateral extension in the posterior sclera was associated with a higher IOP increase during a given volume infusion. This result provided preliminary experimental evidences to the link between corneoscleral biomechanics to IOP dynamics, which may play an important role in understanding IOP-associated glaucomatous damage. Future studies with a larger sample size are needed to verify these results..
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