Regional Deformation of the Optic Nerve Head and Peripapillary Sclera During IOP Elevation

Abstract

PurposeTo measure the deformation of the porcine optic nerve head (ONH) and peripapillary sclera (PPS) in response to intraocular pressure (IOP) elevation.MethodsHigh-frequency ultrasound was used to image the ONH and PPS of 12 porcine eyes during ex vivo inflation testing from 5 to 30 mm Hg. A speckle tracking algorithm was used to compute tissue displacements in the anterior-posterior direction and expansion of the scleral canal. Through-thickness, in-plane, and shear strains were calculated within the ONH. Regional displacements and strains were analyzed and compared.ResultsThe ONH and PPS showed overall posterior displacement in response to IOP elevation. Posterior displacement of the ONH was larger than and strongly correlated with the posterior displacement of the PPS throughout inflation testing. Scleral canal expansion was much smaller and leveled off quicker than ONH posterior displacement as IOP increased. Through-thickness compression was concentrated in the anterior ONH, which also experienced larger in-plane and shear strains than the posterior ONH. Within the anterior ONH, all three strains were significantly higher in the periphery compared with the center, with the shear strain exhibiting the greatest difference between the two regions.ConclusionsHigh-resolution ultrasound speckle tracking revealed the full-thickness mechanical response of the posterior eye to IOP elevation. A mismatch in posterior displacement was found between the ONH and PPS, and regional analyses showed a concentration of strains within the periphery of the anterior porcine ONH. These deformation patterns may help in understanding IOP-associated optic nerve damage and glaucoma susceptibility.

Continuous intraocular pressure monitoring in patients with obstructive sleep apnea syndrome using a contact lens sensor

“…How these IOP fluctuations can contribute to the onset and progression of glaucoma is not completely understood. It is believed that the IOP increase could directly damage the optic nerve but also this elevation could affect the blood flow indirectly harming the optic nerve [34][35][36]. Finally, it has been described that astrocytes in the optic nerve head are mechanosensitive and can respond to the mechanical stress induced by IOP increase, reducing the trophic support or changes in extracellular remodeling in the optic nerve [37,38].…”

Lamina cribrosa pore movement during acute intraocular pressure rise

“…7 In a clinical study on optic nerve head changes during an acute IOP rise, we observed a thinning mainly of the prelaminar tissue, while the lamina cribrosa showed morphological changes mostly with an IOP elevation by >15 mm Hg. 9 Applying sonography, Pavlatos et al 20 found that a posterior displacement of the sclera and optic nerve head was associated with the IOP in a non-linear manner. The current study suggested that the IOP rise-associated displacement in the lamina cribrosa may occur in the anterior-posterior direction (ie, thinning of the prelaminar tissue and backward bowing of the lamina cribrosa) and in the frontal plane leading to a lateral movement of the LCPs.…”

Quantitative confocal optical coherence elastography for evaluating biomechanics of optic nerve head using Lamb wave model

“…9 There are several experimental techniques currently being used to investigate changes in the mechanical compliance of the ONH and posterior scleral surface. 10,11 Most of these identify the pressure-induced deformation at the level of the LC and use this information to determine the biomechanical properties of the tissue. 10 However, it is known that the ONH and anterior laminar surfaces are not only displaced posteriorly but also anteriorly (with reference to Bruch's membrane opening) in a significant portion of glaucoma patients.…”

“…10,11 Most of these identify the pressure-induced deformation at the level of the LC and use this information to determine the biomechanical properties of the tissue. 10 However, it is known that the ONH and anterior laminar surfaces are not only displaced posteriorly but also anteriorly (with reference to Bruch's membrane opening) in a significant portion of glaucoma patients. 12 Characterizing elasticity of the ONH over physiological pressures may provide a better understanding of how changes in IOP lead to changes in the mechanical environment of the ONH.…”