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T.A. Silvestrini, P.M. Pinsky, B. Christie; Analysis of Glucose Diffusion Across the Acufocus Corneal Inlay Using a Finite Element Method . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2195.
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Purpose: To estimate the steady state glucose concentration profile in a cornea implanted with the AcuFocus Corneal Inlay (ACI), a device designed to restore near vision. Methods: The finite element method was used to model the steady–state Fickian diffusive transport of extracellular glucose across a cornea implanted with a thin, microperforated, semi–opaque membrane designed to treat presbyopia. As glucose diffuses across the cornea from the endothelium to the epithelium, it is partially consumed by keratocytes at rates that depend on the level of extracellular glucose. Based on published experimental data, a model for glucose consumption is incorporated by the addition of a nonlinear sink term in the diffusion equation. The aqueous provides the corneal glucose source and it is assumed that the glucose concentration is uniform and constant at the stroma–Descemet's membrane interface. At the epithelium, experimental evidence indicates that glucose consumption by the epithelial cells is proportional to the extracellular glucose concentration and this is incorporated through a boundary condition that relates glucose normal flux to the extracellular glucose concentration. The non linear finite element solves for the glucose concentration over a representative region of the cornea taking into account the full three–dimensional details of the microperforations in the implanted device. Results: Steady state glucose concentration profiles determined for ACIs positioned at depths of 5, 65, and 120 microns in the cornea showed a drop in the glucose level at the corneal epithelium of between 5% and 40%, depending on the spacing of the micro perforation pores. The model provides a detailed view of extracellular glucose transport in the vicinity of the pore holes in the implanted device and can provide useful guidance in the creation of optimal designs for the implant microperforations. Conclusions: The dimensions and permeability of the ACI appear to allow good nutritional flow of glucose throughout the cornea. The model provides a complete understanding of how the design variables of the ACI affect glucose levels in the cornea.
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