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P. D. Hamilton, M. Reilly, N. Ravi; Viscoelastic Behavior of the Lens Soluble Proteins. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3830.
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© ARVO (1962-2015); The Authors (2016-present)
This work is an extension and validation of work previously presented on lens crystallin viscoelasticity1 to increase our understanding of this subject which is essential for gaining insight into the process of accommodation.
Fresh porcine lenses were decapsulated and lenses were homogenized. This homogenate was ultracentrifuged to separate the soluble and insoluble proteins. The viscoelastic behavior of the lens soluble proteins was characterized using a cone-and-plate rheometer at 37°C in steady shear, creep, and dynamic protocols.
The lens soluble proteins exhibit a large degree of shear thinning, with a low-shear asymptotic viscosity of 28.1 Pa-s. They behave as a liquid under all conditions, exhibiting a minimum loss tangent at a frequency of 0.65 Hz. In the included graph, the viscosity in the creeping flow regime is fitted with the Krieger-Dougherty equation for concentrated nonspherical particles. Equilibrium viscosity measurements were modeled using the rate process-based Powell-Eyring model, which describes the shear-thinning behavior of viscoelastic suspensions.
The lens soluble proteins contribute to the viscous portion of the lens’ viscoelastic behavior. The sigmoidal shape of the equilibrium viscosity - shear rate relationship indicates two primary flow regimes. At low shear rates, interparticle forces dominate, resulting in a very high viscosity. As shear rate increases, the inertial forces dominate, destroying non-covalent or weak interactive forces between the crystallin molecules, and the viscosity approaches that of the solvent. The excellent fit of the Powell-Eyring model indicates that the dispersion behaves as a viscoelastic suspension. Shear thinning behavior allows large changes in accommodation to occur with less force than would be necessary if the fluid behaved as a Newtonian fluid.1. Rapp B, Hamilton P, Ravi N. Insights into lens viscoelasticity. Invest. Ophth. & Vis. Sci. ARVO, PN729, 2005.
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