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H. Michail, G. Perry, P. Hamilton, H. Aliyar, N. Ravi; Development of a multi–axial stretcher for measuring the mechanical properties of the lens . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1726.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: In our continuing effort to understand the dynamics of accommodation, we are seeking to characterize the viscoelasticity of the lens. Using the porcine lens, past studies have included static stress–strain scans and creep–recovery experiments using a Dynamic Mechanical Analyzer 7e, (Perkin Elmer). We also have presented data obtained from a custom designed uniaxial stretcher, (ARVO abstract 250, 2003). To further advance our studies, we now have developed a four arm radial stretcher, each containing a strain gauge. Using this we can more accurately mimic the ciliary body as a mechanical analog. This stretcher is equipped with stepper motors for slow stretch, and solenoids with controlled stroke length for impulse stretches all controlled by a custom script running on a Cambridge Electronic Design (model 1401 plus) data acquisition system with their Spike2 software. This will enable us to validate past static stress data and give us stress–relaxation information to further model the viscoelastic character of the lens. Methods: Pig eyes obtained from the local abattoir were dissected. The intact lens, capsule, and ciliary body were removed. Tissue anchoring pins were placed radialy in the ciliary body and the lens was stretched using the four–arm prototype stretcher. The arms operate in a stress–strain and stress–relaxation mode. The stress decay spectra, primarily of the lens, as a function of time was obtained for one second. Results: Pictured is an example of a one second relaxation curve obtained from the stretcher. The arms move a known distance and a strain gauge in each arm measures the corresponding force exerted by the stretched lens. We obtained time constants in the range of 20ms (A) suggesting lens relaxation, and 600–700ms (B) originating from th ciliary body involvement. View OriginalDownload SlideView OriginalDownload Slide Conclusions: Our four–arm prototype has gathered useful data, which can be used for investigating stress relaxation of the porcine lens.
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