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A. Langenbucher, A. C. Schröder, B. Seitz, T. Eppig; Calculation of Optical Performance With Individualized Aspheric Intraocular Lens Design. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5734.
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In the last decade different aspheric intraocular lens designs have been launched to the market for enhancement of optical performance. Most of these concepts are based on model eyes or on normal values for the corneal architecture and ocular measures. The aim of the study was to investigate the best-fit aspheric intraocular lens design for different ocular geometries with respect to image quality and robustness for far and near distance vision.
For exemplary modelling, we defined a model eye with a 2-surface cornea (meniscus lens), an aperture stop and a 2-surface intraocular lens. Corneal front and back surface data, central corneal thickness, axial length and phakic ACD were measured. IOL position was estimated from axial length and phakic ACD, and IOL front surface, central thickness and refractive indexes were predefined (extracted from a schematic model eye). Both corneal surfaces and the anterior IOL surface were characterized by a quadric function and a bundle of rays was traced through the eye equalizing the optical path length from an object to the fovea. Software was written in MATLAB (version 6.5).
For each ray passing through the pupil we derived the location of the individual posterior IOL surface by keeping the cumulative optical pathway through all optical media constant. This posterior IOL surface was fitted by a quadric surface and the ray bundle was traced through the entire optical system to the fovea. For our exemplary calculations, fitting error/optical path differences ranged in between ±2 µm/±200 nm. The retinal spot diameter (ignoring diffraction) increased from around 1 µm to 25 µm for a (point) object approximated from -infinity to -33 cm (reading distance).
Raytracing through quadric surfaces is a very simple and efficient strategy for calculating the individual best-fit aspheric IOL design, if the corneal architecture and biometry of the eye are known. In a next step, the impact of decentration and tilt of the surfaces on the stability of the model and optical performance will be investigated. Further steps will expand the model to arbitrary functional surface descriptors.
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