Optical ray tracing for the calculation of optimized corneal ablation profiles in refractive treatment planning.

PURPOSE Optical calculations have shown that wavefront-based ablation profiles as well as intraocular lens (IOL) implantations can cause residual aberrations or even induce significant additional aberrations due to the poor registry between the eye's optical components. These effects can be exacerbated in eyes that require higher corrections. Individualized eye models can provide accurate ablation profiles for these cases. The aim of this report is to analyze the relevance of individualized eye models for refractive treatment planning from a theoretical point of view. METHODS A method for the customization of eye models based on various types of measurement data of a specific patient is presented and the calculation of optimal ablation profiles and IOL shapes by means of ray tracing through customized model eyes are discussed. Topography data with an original centration on the corneal apex were aligned on the pupil center for the creation of eye models. RESULTS An ideal ablation profile or a customized IOL can be calculated based on the obtained individualized eye models. Calculations have shown that in theory ray-tracing optimized ablation profiles do not leave any residual aberrations in the eye whereas wavefront-guided corrections were found to have the potential to increase specific types of aberrations by a factor of two. This is due to the negligence of the multi-lens structure of the eye. CONCLUSIONS Optical ray tracing algorithms allow the highest degree of customization. The systematic induction of higher order aberrations by means of wavefront-guided treatments or standard IOLs has to be overcome by such a method. However, these theoretical observations must be compared to the corresponding measurement accuracies and precisions and they must be supported by future clinical trials.