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Yanhui Ma, Elias Pavlatos, Xueliang Pan, Sunny Kwok, Keyton Clayson, Jun Liu; Age-related increase in anterior optic nerve head compression in response to IOP elevation. Invest. Ophthalmol. Vis. Sci. 2019;60(9):2246.
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© ARVO (1962-2015); The Authors (2016-present)
To quantify the regional mechanical responses of human optic nerve head (ONH) and peripapillary tissue (PPT) and to investigate age-associated changes in the mechanical responses.
Inflation tests were performed in 15 human donor eyes (age: 20-78 years old) with intraocular pressure (IOP) increase from 15 to 17, 19, 22, 25 and 30 mmHg and a 10 min equilibration at each step. A 3D volume of posterior eye centered at the ONH (10 mm × 10 mm) was scanned at each pressure step using a 50MHz ultrasound probe (MS700, Vevo2100, VisualSonics). A correlation-based 3D speckle tracking algorithm (Cruz Perez et al, ABME, 2015) was used to compute tissue displacements, and the Green strain tensor in the Cartesian coordinate was calculated using least squares estimation. Through-thickness (TT), circumferential, meridional and shear strains in spherical coordinates were obtained by coordinate transformation. Average regional strains at 30 mmHg were obtained and their association with age was evaluated using Pearson correlation.
Compressive TT strains were observed both in the ONH (-2.18%±0.53%) and the PPT (-3.15%±0.68%) with a much larger magnitude compared to circumferential strains (0.05%±0.14% in ONH and 0.13%±0.07% in PPT) and meridional strains (0.30%±0.18% in ONH and 0.16%±0.13% in PPT). Through-thickness compression was concentrated in the anterior region (Fig.1). The magnitude of compressive TT strain in the anterior ONH was positively correlated with age (R=0.56, p=0.028), while ONH in-plane shear strain appeared to be negatively correlated with age (R= -0.50, p=0.055, Fig.2).
Previous studies have shown an age-related stiffening in the collagenous tissue of the posterior eye. Our study showed an age-related decrease in ONH shear (i.e., stiffening); however, through-thickness compression increased with age in the anterior ONH, which is largely composed of glial cells and neural tissue. This result may provide new insights into the age-associated biomechanical susceptibility to glaucoma, particularly in the anterior ONH where glaucoma damages initiate.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Fig.1 Ultrasound images (top) and TT strain maps (bottom) for 2 human donor eyes: 24 yo (left) and 78 yo (right). Cross-section is in the inferior-superior direction at the central plane of scanned 3D volume
Fig.2 A. Compressive strain increased with age in anterior ONH; B. in-plane shear decreased with age in ONH
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