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Edgar Janunts, Marc Kannengiesser, Achim Langenbucher; Individualization of IOLs in a Biconic Eye Model. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6180.
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© ARVO (1962-2015); The Authors (2016-present)
The purpose of the presented work is to introduce a mathematical approach for customizing an intraocular lens (IOL) by optimizing one surface of the lens based on the individual topographic and biometric measurement data. The new lens has predefined anterior surface and a customized free form posterior surface, which compensates the asphericity and toricity of the eye.
The model is defined by biconic anterior and posterior corneal surfaces, a pupil function, predefined 2nd order rotationally symmetric anterior lens, the central lens thickness, and the axial length. Bunch of radially distributed light rays are originated at the virtual plane before the anterior cornea and traced thorough the optical surfaces to the anterior lens surface by computing the ray-surface intersection, the surface normals and the refracted ray directions. The intersection points at the posterior lens surface are derived by applying an optimization algorithm in terms of minimizing the optical path length difference between the rays. Spot diagrams at the retinal plane are obtained by forward raytracing after a fitting the optimized IOL back surface by biconic function by using Levenberg-Marquardt non-linear fitting algorithm.
The simulations are set to a 6 mm zone with a pupil aperture of 4 mm. 10800 rays are calculated (100 µm radial distance, azimuthally 1° steps). Refractive indices of the cornea/posterior chamber/lens/posterior chamber are considered 1.377, 1.337, 1.460, and 1.336. The central lens thickness set to 1mm and the axial length (reference length) to 24 mm. Optical path lengths difference error was smaller than nm. The peak-to-valley/root mean square fitting error of the back IOL surface yield 1.2 µm / 0.506 µm.
Customized IOLs based on the biconic corneal geometry and predefined anterior lens surface has the potential to overcome the limitations of the current IOL concepts and provide significant benefits for image performance. Biconic surface models are proven to yield clinically more relevant representation of the corneal refractive properties. In the presented model the effect of decentration and tilt of customized IOLs into the image quality could be studied. For further proof of concept the model will be applied to clinical data.
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