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S. Barbero, S. Marcos, V; Analytical Tools for Intraocular Lens Design With Aspheric Surfaces. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3130.
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© ARVO (1962-2015); The Authors (2016-present)
To present a complete methodology to develop Intraocular Lens (IOL) designs and evaluate their performance based on an analytical formulation. To explore the possibilities of the methodology to propose more efficient optical designs using aspheric surfaces.
The analytical formulation is based on Gaussian and third-order aberration theory applied to a pseudoaphakic eye model. The model used in the computations is composed of a multilayer cornea and an IOL with homogenous refractive index and aspheric surfaces. Explicit relations of the defocus and spherical aberration coefficients as a function of the different parameters of the model (pupil radius, IOL surfaces radii of curvature and asphericities, thickness and refractive index) are derived. From these equations the Root Mean Square (RMS) of the wave aberration and the equivalent defocus (Me) is computed and used as an optical metric.
The derived equations allow representation as bi-dimensional graphics of the IOL optical performance as a function of IOL anterior and posterior surface radii of curvature (Ra and Rp) and asphericities (Qa and Qp). These graphics show specific regions where the combination of the different parameters produce acceptable performance. Furthermore, robust analytical optimization algorithms were used to search for the optimal combination of radii and asphericities. Additionally, it is possible to impose constraints on any of the IOL parameters (driven from manufacturing or biomechanical limitations) and to search the optimal values for the other parameters. As an example, for a specific eye model, we obtained the optimal monofocal spherical IOL design (n=1.55, thickness=0.667 mm) for a 3-mm pupil diameter as a meniscus (Ra=8 mm, Rp=91 mm) or biconvex lens (Ra=10 mm, Rp=-66.6 mm), producing an equivalent defocus, Me, of ~0.25. Introducing asphericities (Qa=-5 and Qp=0, for example) Me can be reduced to 0 D.
An analytical procedure is presented to obtain optimal spherical/aspheric IOL designs, allowing a graphic visualization of the performance as a function of the design parameters, as well as analytical optimization tools and a tolerance analysis. The strength of the procedure is the straightforward analysis of the optical performance of generic designs without the use of expensive blind ray tracing routines. The methodology can be extended off-axis and to multifocal designs.
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