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Baptiste Coudrillier, Diogo M Geraldes, Nghia Vo, Julie Albon, Richard L Abel, Ian Campbell, C Ross Ethier; A novel micro-computed tomography (μCT) method to measure IOP-induced deformation of the Lamina Cribrosa (LC) . Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):6149.
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© ARVO (1962-2015); The Authors (2016-present)
To determine high-resolution, acute, IOP-induced deformation of LC beams, relevant to the mechanobiology of glaucoma.
Two porcine eyes and 7 human donor eyes were received within 24 hours of death and stored at -4◦C. Unfixed posterior poles were inflated to 6, 15, 22, and 30 mmHg using custom built pressurization chambers. High-resolution phase-contrast μCT scans were performed at the beamline I12-JEEP, Diamond Light Source (53 keV, 3600 projections, 0.08s exposure time, 2.56 μm isotropic resolution). LC beams were segmented in 3D, following Frangi’s filter image processing to determine beam position and LC microarchitecture. Histograms of pore size, pore density, and LC beam thickness were generated using Matlab and compared between IOP levels. The central cross-sections of the LC were manually delineated to determine the pressure-induced change in LC shape. Full-field 3D measurement of strains within the LC was achieved using digital volume correlation (DVC, LaVision).
LC beams in high-resolution 3D scans of the entire unfixed LC were successfully segmented (Fig 1). The porcine LC mechanical response to IOP was nonlinear with largest deformation occurring between 6 and 15 mmHg. Elevated IOP was associated with a decrease in pore size, thinning of the LC beams and sclera, and posterior displacement of the LC. DVC measured strains with an accuracy of 0.1%. Mean first principal strain in the pig LC due to IOP increasing from 6 to 15 mmHg was 3.3% (range: 1.2-6.9%, Fig 2).
Phase-contrast μCT is a powerful tool to measure 3D changes in shape and microarchitecture of the human and porcine LC induced by increased IOP. Segmentation methods and algorithms to compute IOP-induced deformations from the 3D scans were validated on the porcine LC and are currently being applied to human LCs.
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