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M Bueeler; Required Accuracy of Lateral and Cyclotorsional Alignment in Aberration Sensing and Customized Treatments . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2059.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To estimate the required alignment accuracy needed in wavefront sensing and customized treatments to achieve a sought level of reproducibility in a certain percentage of the normal population. Methods: The effect of misalignment on the optical outcome was simulated by applying coordinate transformations to measured wavefront aberration patterns of 130 normal eyes. Simulations included lateral decentrations and rotations around the longitudinal axis (cyclotorsion). The optical quality of the simulated correction was rated by means of the root-mean-squared residual wavefront error. Results: The required accuracy for lateral centration to achieve the diffraction limit at a pupil size of 8 mm in 95% of the investigated eyes should be 50 microns or better. However, an accuracy of 450 microns was found to be enough to guarantee that none of the investigated eyes would suffer from a decreased optical performance after surgery. Alignment would have to be performed with a cyclotorsional precision of approximately 1 deg or better in order to achieve the diffraction limit in 95% of the measured normal eyes for an 8-mm pupil, whereas an accuracy of 15 deg is required to obtain some improvement of the optical quality in all the examined eyes. The accuracy needed for cyclotorsional alignment increases compared to pure sphero-cylindrical treatments when additional correction of the higher-order aberrations is aspired. Conclusion: A high reproducibility of the torsional alignment between the measurement and the treatment has to be provided to justify the choice of a wavefront-guided treatment over a classical treatment. Using systems, that do not feature special alignment procedures linking the alignment information of the measurement with the one of the treatment, the goal of an ideal i.e. diffraction limited correction might only be achieved in a small fraction of the treated eyes.
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