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Xin Gao, Qiaoqiao Zhu, Weiyong Gu; Effects of variation of hydration and glycosaminoglycan content on the flow facility in trabecular meshwork. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5662.
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In glaucomatous eyes, the increased deposition of the extracellular matrix (ECM) component and the decreased glycosaminoglycan (GAG) content within the trabecular meshwork (TM) have been reported. The deposition of ECM may narrow the pathways for transporting aqueous humor. The depletion of GAGs will lead to the reduction of the amount of fixed charges which are attached to GAG. These fixed charges can cause the TM swelling, which can broaden these transport pathways. The objective of this study was to develop a quantitative model to characterize the effects of hydration and GAG content [or fixed charge density (cf)] within TM on the transport of aqueous humor.
A 3D numerical model was developed to quantitatively characterize the effects of hydration (φw) and GAG content on aqueous humor dynamics in human TM. This model was based on the continuum mixture theory (Lai et al, 1991) and finite element method. The constitutive models for permeability and elasticity were hydration-dependent. The pressure difference was applied as boundary condition across a realistic human TM geometry. The flow facility was calculated with a physiological fluid flux (2.25 µL/min).
Our simulated results for flow facility and Young’s modulus for TM with hydration (φw) in the range from 0.944 to 0.974 were consistent with those reported in healthy and glaucoma eyes (Fig. 1a). The small reduction of hydration (~3%) has significant effects on flow facility (~93% decrease) and elasticity (~10 times increase). The flow facility decreased only ~10% when fixed charge density decreased from 30 mM to zero at healthy (φw=0.972) with 2.25 µL/min fluid flux (Fig. 1b).
Alteration of the hydration has significant effects on the flow dynamics and the mechanical properties of TM. However, from the biomechanical point of view, the depletion of GAG content has limited impact on the transport of aqueous humor in TM.
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