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Ian A. Sigal, Jonathan Grimm, Korey Reid, Donald J. Brown; Median Pore Size And Beam Thickness Are Good Predictors Of Median IOP-Induced Shear Strain Within The Lamina Cribrosa Microarchitecture. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3184.
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To measure eye-specific displacements and deformations (stretch, compression and shear) induced within the lamina cribrosa (LC) microstructure of human eyes by increases in IOP.
Five human eyes from three donors aged 54 to 82 were scanned using second harmonic generated (SHG) imaging (Zeiss 510 Meta LSM). The optic nerves were cut to allow imaging of the LC from the posterior direction. Images up to a depth of 300 µm (2 µm resolution) were acquired at IOPs ranging from 10 to 50 mmHg, after allowing equilibration for 30 min. Mosaic lateral resolution varied from1.76 to 4.97 µm/pixel. Digital image correlation techniques were used to calculate the deformation mapping between maximum intensity projection images at low and at elevated IOP, and the measurements analyzed globally and split into eight 45° regions. Beam thickness and pore size were measured through scripted image processing (Fiji).
IOP-increases produced substantial displacements and biologically relevant deformations within all the eyes (Table). There were significant variations between eyes (P’s<0.0001, nested ANOVA) and between regions of a given eye (P’s<0.0001) (Figure), although contralateral eyes were more similar than unrelated eyes (P’s<0.0001). Larger displacements, stretch, compression and shear often did not colocalize. Median shear strain was strongly and significantly correlated with both median beam thickness (adjusted-R2= 0.96, P<0.003) and median pore size (0.95, P<0.003) separately, and simultaneously (0.999, P<0.007). Stretch and compression were modestly correlated and displacement magnitude weakly correlated with pore size and beam thickness.
We measured eye-specific IOP-induced displacements and deformations of the pores and beams of the LC in uncut and unfixed human eyes with unprecedented detail. Median pore size and beam thickness were excellent predictors of median LC shear and modest predictors of median stretch and compression, suggesting that LCs with thick beams and/or large pores may be more sensitive to elevated IOP.
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