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3d Biomechanical Response of the Optic Nerve Head: Initial Results From Porcine Globe Inflation Using High-frequency Ultrasound Elastography.

Characterization of the biomechanical behavior of the optic nerve head (ONH) in response to intraocular pressure (IOP) elevation is important for understanding glaucoma susceptibility. In this study, we aimed to develop and validate a 3D ultrasound elastographic technique to obtain mapping and visualization of the 3D distributive displacements and strains of the ONH and surrounding peripapillary tissue (PPT) during whole globe inflation from 15 to 30 mmHg. 3D scans of the posterior eye around the ONH were acquired through full tissue thickness with a high frequency ultrasound system (50 MHz). A 3D cross-correlation based speckle-tracking algorithm was used to compute tissue displacements at ~30,000 kernels distributed within the region of interest, and the components of the strain tensors were calculated at each kernel by using least square estimation of the displacement gradients. The accuracy of displacement calculation was evaluated using simulated rigid-body translation on ultrasound radiofrequency data obtained from a porcine posterior eye. The accuracy of strain calculation was evaluated using finite element models. Experimental data in porcine eyes showed that ONH deformation was heterogeneous with localized high strains. Substantial compression was observed in the anterior ONH and out-of-plane shear was shown to concentrate in the vicinity of ONH/PPT border. These preliminary results demonstrated the feasibility of this technique to achieve comprehensive 3D evaluation of the mechanical responses of the posterior eye, which may provide mechanistic insights into the regional susceptibility in glaucoma.