Abstract
Abstract: :
Purpose: The purpose of this study is to determine the induced postoperative aberrations in waveguided surgery due to the centration errors. These errors lie in the modification of the coordinate system between ocular wavefront measurement and ablation procedure. Methods: A computer analysis of the corrected eye sensitivity to the centration errors has been performed using a wavefront-eye model applied to 21 synthetic eyes characterized by different preoperative individual aberration, i.e. defocus, astigmatism, coma, spherical aberration, as well as by composite aberration patterns. The centration errors we have taken into consideration are decenter, tilt and torsion, acting individually and composed. This customized eye model is composed of a perfect-eye lens followed by a phase surface that transforms the parallel monochromatic beam into the ocular wavefront. The refractive correction is simulated by the conjugate phase surface added to the wavefront-eye transforming the aberrated ocular wavefront into a plane wave. In order to double-check the results of the sensitivity analysis a second eye model has been used. This eye model employs the concept of a thin lens defined by the removed corneal tissue and delimited between pre- and postoperative outer corneal surfaces. This lens has been named "Removed-Stroma-Lens" (RSL). Results: Some general remarks related to aberrations induced by centration errors have been pointed out. Each combination of an individual preoperative aberration with an individual error induces a particular postoperative aberration pattern. The coefficients of induced Zernike spectrum vary independently with each error and preoperative Zernike spectrum. The final aberration pattern induced by a composite preoperative Zernike spectrum with a composite error can be seen as a weighted sum of aberrations induced by each combination of an individual preoperative aberration with an individual error. The eyes most sensitive to the centration errors are the eyes having preoperative coma or/and spherical aberration. Conclusion: The results of this analysis in conjunction with a table of tolerances of the postoperative ocular aberrations can provide the requirements of centration accuracy in waveguided treatments.
Keywords: 544 refractive surgery • 550 refractive surgery: optical quality • 547 refractive surgery: corneal topography