We characterized the stiffness and anisotropy of the equatorial sclera and its dependence on intraocular pressure (IOP). Porcine eyes were tested using ultrasound elastography under IOP control. Shear waves were induced using a mechanical shaker, and an off-axis 17.8 MHz transducer used to track the wave propagation in the equatorial and anterior-posterior directions. Wave speed was measured and used to estimate directional Young’s moduli. Anisotropy was defined as the ratio of the equatorial moduli to the anterior-posterior moduli. Sclera was stiffer in the equatorial direction, with anisotropy decreasing with IOP, from, 5.1 at 10 mmHg to 3.7 at 30 mmHg.
The mechanosensitivity of the optic nerve head (ONH) plays a pivotal role in the pathogenesis of glaucoma. Characterizing elasticity of the ONH over changing physiological pressure may provide a better understanding of how changes in intraocular pressure (IOP) lead to changes in the mechanical environment of the ONH. Optical coherence elastography (OCE) is an emerging technique that can detect tissue biomechanics noninvasively with both high temporal and spatial resolution compared with conventional ultrasonic elastography. We describe a confocal OCE system in measuring ONH elasticity in vitro, utilizing a pressure inflation setup in which IOP is controlled precisely. We further utilize the Lamb wave model to fit the phase dispersion curve during data postprocessing. We present a reconstruction of Young’s modulus of the ONH by combining our OCE system with a Lamb wave model for the first time. This approach enables the quantification of Young’s modulus of the ONH, which can be fit using a piecewise polynomial to the corresponding IOP.
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