Biomechanical interplay between lamina cribrosa and peripapillary sclera characterized by 3D ultrasound elastography

The lamina cribrosa (LC) and peripapillary sclera (PPS) form a biomechanical structure whose response to intraocular pressure (IOP) is central to glaucomatous optic nerve damage. Computational models predict strong biomechanical interactions between PPS and LC, yet experimental validation in human eyes has remained limited, particularly for full-thickness characterization. In this study, we applied 3D high-frequency ultrasound elastography technique to quantify full-thickness deformation of PPS and LC and to characterize their biomechanical interplay under controlled IOP elevation. Inflation testing from 15 to 30 mmHg was performed in 22 human donor whole globes. At each pressure step, 3D radiofrequency ultrasound data was acquired and analyzed using a validated speckle-tracking algorithm to estimate full-field tissue displacements and calculate the spherical Green-Lagrange strain tensor. PPS and LC boundaries were manually segmented on radial reconstructions to enable region-specific strain and morphometric analyses. Our results showed that IOP-induced shear strains were significantly correlated between the PPS and LC (all r > 0.6, P < 0.01). Among the morphometric parameters, PPS radius of curvature was correlated with all PPS and LC shear strains (r: 0.54 to 0.71). PPS thickness was negatively correlated with PPS out-of-plane shear strains (r: -0.44 to -0.48). LC depth was correlated with LC shear strains (r: 0.42 to 0.46), and LC thickness was correlated with PPS shear strains (r: 0.54 to 0.56). These findings provide experimental evidence that PPS/LC biomechanical coupling under IOP elevation is associated with shear deformation. Quantifying PPS and LC shear behavior may improve understanding of optic nerve head biomechanics and facilitate discovery of new biomechanical biomarkers relevant to glaucoma susceptibility.