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SR Evans, EB Papas, BA Holden; Computational Fluid Dynamics Model of the Contact Lens and Tear Film Under Normal Pressure . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3098.
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Purpose: To assess the effects of normal pressure on the tear flow pattern in the post-lens tear layer. A continuous viscosity profile for the tear film is also constructed for use in this and other studies. Methods: Computational fluid dynamics techniques have been used to construct a pressure-forced model of the contact lens and tear film. Viscosity/shear rate measurements of tears and mucin (Pandit et al, Exp. Eye Res. 68:247, 1999) were fitted to the Bird-Carreau viscosity model (Chem. Eng. Sci 23:427, 1968), then interpolated to produce a continuously varying viscosity profile for the tears. A layer of tears was placed between a flexible contact lens and a solid cornea. The resulting finite-volume model was forced by pressure normal to its anterior boundary, as in the closed eye. Results: The geometric features of the lens and cornea produce a tear flow pattern with several significant features. Quiescent zones and regions of reversed flow occur. The shear stresses felt at the ocular surface are comparable to those resulting from the shear forces occurring during blinking, based on previous models. Conclusion: Small geometric features of the lens may have a significant effect on the character of the tear exchange under contact lenses, with consequences for the efficiency of fluid and solid flushing. While blinking may be intuitively seen as the only significant cause of shear stresses under the contact lens, we show that normal pressure alone can also result in stresses of similar magnitude.
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