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Jonathan Grimm, Richard Bilonick, Hiroshi Ishikawa, Gadi Wollstein, Larry Kagemann, Joel Schuman, Ian Sigal; Lamina Depth and Pia Insertion are Significant Factors in Optic Nerve Head Biomechanics. Invest. Ophthalmol. Vis. Sci. 2013;54(15):62.
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© ARVO (1962-2015); The Authors (2016-present)
Variations in eye anatomy, such as lamina cribrosa depth and the length of its insertion into the pia mater, have been postulated to affect optic nerve head (ONH) sensitivity to elevated IOP. Our goal was to determine how lamina cribrosa depth and lamina insertion into the pia, among other characteristics of the ONH, influence ONH biomechanics.
We adapted a previously reported finite element model of the eye (IOVS. 2011; 52:5497-506) to incorporate variations in anterior laminar insertion depth (relative to the scleral canal opening), lamina curvature and thickness, scleral canal opening radius, pia mater thickness and the stiffness of the sclera, lamina and pia mater (through the Young’s modulus). The length of the lamina insertion into the pia mater was computed for each ONH. Using a Design of Experiments technique we defined a population of 2603 ONHs. For each one we computed the biomechanical effects on the lamina cribrosa of an increase in IOP of 10 mmHg, and extracted the mean and peak tensile, compressive and shear strains and the von Mises stress. Statistical models allowing up to third order interactions were computed to determine the effects of each parameter on the responses.
Anterior lamina depth accounted for 12% of the variance of mean and peak tensile strain. Increased anterior lamina depth resulted in higher peak (up to 2%) and lower mean (up to 0.5%) tensile strains, and lower mean von Mises stress (up to 10 kPa). Scleral canal opening radius, scleral stiffness and lamina stiffness often had strong and significant interactions with anterior lamina depth. The length of the pia insertion was a significant factor for both the strains and the stresses (all p<0.000001).
Lamina depth and length of lamina insertion into the pia are significant factors in lamina biomechanics. Interestingly, our results suggest that a posterior remodeling of the lamina cribrosa may have both strain-increasing and strain-decreasing effects.
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