Abstract
Aim/Purpose: Previous studies have shown that the trabecular meshwork (TM) is mechanically stiffer in glaucomatous eyes as compared to normal eyes. It is believed that elevated TM stiffness increases resistance to the aqueous humor outflow, producing increased intraocular pressure (IOP).It would be advantageous to measure TM mechanical properties in vivo, as these properties are believed to play an important role in the pathophysiology of glaucoma and could be useful for identifying potential risk factors. The purpose of this study was to develop a method to estimate in-vivo TM mechanical properties using clinically available exams and computer simulations.Design: Inverse finite element simulationMethods: A finite element model of the TM was constructed from optical coherence tomography (OCT) images of a healthy volunteer before and during IOP elevation. An axisymmetric model of the TM was then constructed. Images of the TM at a baseline IOP level of 11, and elevated level of 23 mmHg were treated as the undeformed and deformed configurations, respectively. An inverse modeling technique was subsequently used to estimate the TM shear modulus (G). An optimization technique was used to find the shear modulus that minimized the difference between Schlemm’s canal area in the in-vivo images and simulations.Results: Upon completion of inverse finite element modeling, the simulated area of the Schlemm’s canal changed from 8,889 μm2 to 2,088 μm2, similar to the experimentally measured areal change of the canal (from 8,889 μm2 to 2,100 μm2). The calculated value of shear modulus was found to be 1.93 kPa, (implying an approximate Young’s modulus of 5.75 kPa), which is consistent with previous ex-vivo measurements.Conclusion: The combined imaging and computational simulation technique provides a unique approach to calculate the mechanical properties of the TM in vivo without any surgical intervention. Quantification of such mechanical properties will help us examine the mechanistic role of TM biomechanics in the regulation of IOP in healthy and glaucomatous eyes.
Highlights
Glaucoma is a major health concern and a leading cause of blindness, affecting more than 3 million people in the US and 63 million people worldwide.[1,2] Globally, the number of glaucomatous bilateral blindness cases is expected to exceed 11 million by 2020;3 it has been estimated that, by 2040, 111.8 million people will have glaucoma worldwide.[1]
Using ex-vivo samples significantly limits the applicability of the measurement as a diagnostic tool in the future. To bridge this knowledge gap, we propose a new method to determine the mechanical properties of the trabecular meshwork (TM) in vivo without the need for any surgical intervention by employing computer simulations and clinically available non-invasive TM imaging techniques
A value of 1.93 kPa was obtained for the TM shear modulus, G
Summary
Glaucoma is a major health concern and a leading cause of blindness, affecting more than 3 million people in the US and 63 million people worldwide.[1,2] Globally, the number of glaucomatous bilateral blindness cases is expected to exceed 11 million by 2020;3 it has been estimated that, by 2040, 111.8 million people will have glaucoma worldwide.[1]. Aqueous humor exits the anterior eye through two pathways: the trabecular meshwork (TM) pathway, accounting for ~60% of the outflow, and the uveoscleral pathway.[5] The TM pathway begins at the apex of the iridocorneal angle. It continues through the trabecular tissue, across the inner wall of Schlemm’s canal, into the canal’s lumen, and into the collector channels. IOP increases with respect to normal conditions both if the resistance to aqueous outflow or the aqueous production rate increases
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