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A. P. Rowley, K. Chen, B. Basinger, J. Weiland, M. Humayun; Mechanical Modeling of an Epiretinal Prosthesis. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4592.
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© ARVO (1962-2015); The Authors (2016-present)
To examine to elastic properties of the human retina, choroid and sclera as well as polyimide and silicone in saline at 37°C, to enable the development of a Finite Element Analysis model of an epiretinal prosthesis.
Twenty human donor eyes were obtained from an eye bank to acquire the necessary samples of retina, choroid and sclera. 10 samples of polyimide and silicone used in an epiretinal prosthesis were also tested. Uniaxial tensile tests were performed in both the horizontal and vertical meridian on the cadaveric material. All samples thicknesses were measured optically prior to stretching in a Bose ELF3100 dynamic mechanical test instrument at 37°C in a saline chamber.
Yield stress, yield strain, low elastic modulus and high elastic modulus of all three tissue layers were calculated. All layers behaved non-linearly, but only the retina exhibited surface anisotropy between the vertical and horizontal meridian. Modeling indicates that an acute tacking force distributes stress primarily around the edges of the electrode array, particularly the edge nearest the cable. Model predictions for one potential chronic loading configuration, where excess cable is included between the incision in the sclera and the electrode array, suggest that stress in that case is concentrated along the edge of the array furthest from the cable. Retinal damage is seen in both locations in a canine model chronically implanted with a similar 16-electrode array.
Mechanical properties of the human eyewall and relevant biomaterials can be used in Finite Element Analysis models to allow researchers to improve design parameters of future retinal prosthesis and other ocular devices.
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