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Daniel G. Brady, Doug Cali, Henk A. Weeber, Ed Geraghty; Evaluation of Key Parameters Providing Dioptric Power Change in an Optic- A Finite Element Analysis. Invest. Ophthalmol. Vis. Sci. 2011;52(14):821.
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The goal of this Finite Element Analysis (FEA) was to identify the key variables and their relative influence on optical power change for a deformable optic accommodating intraocular lens.
Non-linear static Finite Element Analysis was performed using Abaqus/Standard simulation software. Various optical-mechanical designs were modeled and evaluated for optic body deformation based on boundary conditions that simulated physiological force conditions. Boundary conditions consisted of 6gF that was applied either as a pressure to the outside surface of the optic (optic edge) or to an intermediate rigid surface that was in frictionless contact with the optic edge. Optical power was calculated using Abaqus output of pre and post deformation optic surface node coordinates for the central 3 mm optic zone. Optical surface data was imported into Zemax for optical quality analysis.
The power change of the optic was affected by 4 key variables. The key variables identified were optic material mechanical properties, optic diameter, optic thickness and refractive index. The most significant variable found was the material mechanical property, i.e. Young’s modulus, which when evaluated by FEA showed that materials,with low Young’s moduli, produced relatively large optical power change when all other variables were held constant. A specific FEA model simulating a lens optic having a Young’s modulus of 5.5kPa resulted in an optical power change of approximately 9D. The power change was also significantly increased by decreasing the optic diameter from 6 mm to 2mm. The thickness of the optic edge also had an affect on the power change of the optic, continuing to increase the power change of the optic up to 4D and leveled off at 5D. Lastly, Refractive index was also shown to be another factor in increasing the power change. The optical analysis using Zemax demonstrated that the optical quality can be maintained when the optic is compressed with 6gF.
The key variables of lens optic material mechanical property and center thickness identified in the FEA simulations show the potential to generate optical power change similar to that produced in the natural crystalline lens. Furthermore, when constrained by the physiological forces available within the eye lens optical materials with a Young’s modulus between 10 to 100 kPA demonstrated optical power change similar to that of a healthy human crystalline lens with an approximated Young’s modulus of 1.5 kPA.
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