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Jun Liu, Ryan Short, Hugh J Morris, Kimberly Metzler, Benjamin Cruz Perez, Richard T Hart, Xueliang Pan; Influence of scleral stiffening on intraocular pressure increase during microvolumetric changes. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):6147.
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© ARVO (1962-2015); The Authors (2016-present)
To examine how a localized alteration of the scleral biomechanical properties affects the whole globe’s response to a controlled change in intraocular volume.
Porcine globes were tested within 48 hours postmortem. Twelve globes were randomized to either a treatment group (local immersion with 4% glutaraldehyde in saline) or a control group (saline only). Each eye was subjected to a one-second infusion of 15 µL of phosphate buffered saline (PBS) before and after the treatment of an area of the posterior temporal region of the sclera and the IOP increase (ΔIOP) was recorded. Inflation tests with ultrasound speckle tracking were performed before and after the treatment to examine the mechanical strains in the treated area of the sclera. An initial computational model using linear elastic material properties was built to predict the effect of scleral stiffening and compare with the experimental results.
The ΔIOP associated with an infusion volume of 15 µL was significantly greater (19.2 ± 3.5 mmHg vs 16.1 ± 2.7 mmHg, p=0.01) after stiffening an area of the sclera. No difference was found in the control group (15.1 ± 3.1 mmHg vs 15.7 ± 2.3 mmHg). Ultrasound speckle tracking showed significant reduction in both axial (by 2.3 fold) and lateral (by 4.3 fold) strains at 25 mmHg in the area of treatment (p<0.05). Computational models based on linear elasticity showed that only when the cornea was of similar modulus as the sclera, scleral stiffening could generate appreciable effects on ΔIOP; while a much more compliant cornea would dominate the outcome during volumetric changes.
The experimental results showed a small but statistically significant increase in ΔIOP during microvolumetric changes in ex vivo porcine globes treated with a collagen crosslinking agent in the posterior sclera. Combined with the computational models and a previous report (Liu and He, IOVS, 2009, 50(5)), corneal and scleral biomechanics affect IOP dynamics but cornea is likely more influential. Future studies will implement viscoelastic tissue properties to examine the rate dependence of the ocular volume-pressure relationship.
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