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Jonathan Pieter Vande Geest, Ehab Tamimi, Jeffrey Pyne, Stephen J Howerton; Optic nerve deformations in normal enucleated human eyes in response to increased intraocular pressure. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3158.
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© ARVO (1962-2015); The Authors (2016-present)
Glaucoma is the second leading cause of blindness worldwide affecting more than 7 million people. Assessment of the optic nerve head as a biomechanical structure may be important for identifying specific mechanisms in glaucomatous optic neuropathy. However, few studies in the literature have focused on measuring experimental strains of the optic nerve head in an inflated eye. In this study, we use an in-house sequential-digital image correlation system (S-DIC) to gather optic nerve deformation data for human posterior scleral shells undergoing pressure inflation. We hypothesize that there are significant differences in ON strains as compared to both PPS and non-PPS regions.
The posterior sclera of eyes from human donors of European descent above 50 years old (n=12) were inflated to intraluminal pressures from 5 to 45 mmHg. The S-DIC system was used to measure deformation data by tracking individual points of a speckle pattern applied to each eye. These measurements were used to create a point cloud for both the sclera and the optic nerve for both pressures. These point clouds were used to create meshes from which in-plane principal green strains were calculated. The geometries were segmented into three regions: the optic nerve (ON), the peripapillary sclera (PPS) and the non-PPS. The 95th percentile E1 and E2 values within these regions were compared.
E1 values of the ON were significantly lower than that of PPS region (p-value = 0.017). E2 values of the ON were significantly lower than both the PPS and the non-PPS regions (p-value < 0.001 for both, Figure 1). Furthermore, a Pearson product-moment correlation was run to determine the relationship between the volume of the ON stump and the principal strain. There was no significant correlation between ON volume and E1 (r = 0.49, p = 0.106) or E2 (r = 0.06, p = 0.852).
Our results indicate that the ON regions experienced less tensile deformation and more compressive deformation compared to scleral regions. Deformations in and around the ON may be important in assessing the biomechanical environment in the context of glaucoma. Future work in our laboratory is focused on identifying if ON strains differ across donor tissues from various racioethnic populations at higher risk for glaucoma.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Figure 1. Left) Principal strains of the various regions; Right) Example distributions of E1 and E2
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