Mechanical Deformation of Human Optic Nerve Head and Peripapillary Tissue in Response to Acute IOP Elevation

Abstract

Purpose To measure the deformation of the human optic nerve head (ONH) and peripapillary tissue (PPT) in response to acute intraocular pressure (IOP) elevation. Methods The ONH and PPT of 14 human donor globes were imaged with high-frequency ultrasonography during inflation testing from 5 to 30 mm Hg. A correlation-based speckle tracking algorithm was used to compute tissue displacements, and the through-thickness, in-plane, and shear strains were calculated by using least-squares strain estimation methods. The ONH and PPT were segmented along the anterior-posterior direction and the nasal-temporal direction. Regional displacements and strains were analyzed and compared. Results The ONH displaced more posteriorly than the PPT in response to an acute IOP increase. Scleral canal expansion was minimal but correlated with ONH posterior displacement at all IOP levels. Through-thickness compression was concentrated in the anterior of both the ONH and the PPT. Shear was concentrated in the vicinity of the canal with higher shear in the peripheral ONH than the central ONH and higher shear in the PPT near the scleral canal than that further away from the canal. Conclusions High-resolution ultrasound speckle tracking showed a displacement mismatch between the ONH and the PPT, larger compressive strains in the direction of IOP loading in the anterior ONH and PPT, and higher shear strains in the periphery of ONH in response to acute IOP elevation in the human eye. These findings delineate the deformation patterns within and around the ONH and may help understand IOP-associated optic nerve damage.

Ocular Pulse Elastography: Imaging Corneal Biomechanical Responses to Simulated Ocular Pulse Using Ultrasound

“…We implemented speckle tracking in RF data with interpolation of correlation coefficients, resulting in displacement sensitivity approaching tens of nanometers. 18,31,32 This high sensitivity enabled the detection of the spatial gradient of displacement despite a small range of magnitudes (i.e., within a few micrometers) (Fig. 3).…”

Scleral structure and biomechanics

“…Tang and Liu (Tang and Liu, 2012) developed an alternative system, in which ultrasound speckle tracking was used to obtain cross-sectional profiles of scleral displacements in a porcine model. This was subsequently adapted successfully for studies in human (Pavlatos et al, 2016) (Ma et al, 2019) (see Fig 19) and canine (Palko et al, 2016) sclera. In contrast to DIC methods, ultrasound speckle tracking does not require the application of particulate markers to the scleral surface, but rather generates intrinsic speckle patterns from acoustic interference of sub-resolution scatterers.…”

Heartbeat-Induced Corneal Axial Displacement and Strain Measured by High Frequency Ultrasound Elastography in Human Volunteers

“…We have implemented a method to densely sample the radiofrequency (RF) data, which are voltage values of the ultrasound signals, to achieve very high displacement sensitivity reaching 10s of nanometers with interpolation. 2 , 6 Second, the OPE technique tracks displacements of many spatial points within the scanned corneal cross-section. Local mechanical strains can be computed from the spatial gradients of the displacements, which may be distinct in ocular diseases, such as keratoconus and glaucoma.…”