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Peter Michael Pinsky, Keith Holliday; Finite element modeling of metabolic species transport in the cornea with a hydrogel intrastromal inlay. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1131.
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Intrastromal inlays for refractive correction of presbyopia are being adopted into clinical practice. An important concern is the effect of the inlay on the long-term health of the cornea due to disturbances in the concentration profiles of metabolic species. A 3-D metabolic model for the cornea is employed to investigate oxygen, glucose and lactate ion transport in the cornea and to estimate changes in species concentrations induced by the introduction of a hydrogel inlay.
A reaction-diffusion metabolic model, appropriate for highly oxygen-permeable hydrogel inlays, is used to describe cellular consumption of oxygen and glucose and production of lactic acid. A three-layer corneal geometry comprising epithelium, stroma, and endothelium, is employed with a hydrogel inlay placed under a lamellar flap. The model is solved numerically by the finite element method. The accuracy of the metabolic model is assessed by comparing predicted glucose consumption rates to experimental measurements for rabbit in vitro. The model is employed to predict concentration profiles in a cornea containing an inlay made from a commercially available hydrogel material.
Predicted glucose consumption rate versus glucose concentration in the normal cornea compared reasonably well with rabbit measurements and confirm the predictive accuracy of the model. For a cornea with a hydrogel inlay having a relative inlay diffusivity of 43.5%, predicted maximum glucose depletion and lactate ion accumulation occur anterior to the inlay and both are less than 3%. A sensitivity study on inlay diffusivity showed that glucose depletion and lactate ion accumulation are insensitive to reductions in inlay diffusivity until the limit of approximately 20% relative diffusivity; below this level, glucose and lactate ion concentrations increase exponentially. For fixed inlay diffusivity, glucose depletion increases slightly with increasing depth of inlay placement.
The flux of metabolic species is modified by an inlay, depending on the inlay relative diffusivity. For commercially available hydrogel materials and a typical inlay design, predicted changes in species concentrations are small when compared to the variation of concentrations across the normal cornea. In general, glucose depletion and lactate ion accumulation are highly sensitive to inlay diffusivity and somewhat insensitive to inlay depth.
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