Experimental and theoretical basis of the differentiated approach to the implementation of aspheric ablation profile with a preset Q-factor using excimer laser device "Microscan-Vizum"
To ground the differentiated approach to the application of aspheric ablation algorithm, conic-constant oriented, using the Russian excimer laser device «Microscan-Vizum», a series of experimental samples of ablation profiles was made on 24 plates of polymethyl methacrylate (PMMA). During the creation of samples we used standard and aspheric ablation profile. Initially different keratometry, a different diameter of the optic zone, a set point Q-factor (of conic constant) were introduced into the parameters of operation. High-precision scanning laser microscope ZYGO model «New Wiew - 5000 ZYGO» (Germany) was used for measuring the depth, profile, the diameter of the ablation of PMMA samples. The method of comparative analysis on a personal computer was used to study the measurement data of the depth, profile and the diameter of the ablation of experimental PMMA samples. Results. After the comparative evaluation, the following was confirmed: - the depths of a standard (spherical) and aspheric ablation algorithm differ by 9.8%. The depth of aspheric ablation at initial value of spherical and cylindrical component equal to zero was approximately 10 microns; - the spherical ablation depth is directly proportional to the value of Q-factor; - if keratometry is in the range of 37 to 39 diopters it is necessary to increase the values of Q-factor for aspheric ablation profile, if keratometry is 47 diopters or more it is necessary to reduce the value of Q-factor or not to use an aspheric algorithm; - the futility is revealed of using aspheric correction if the optical zone diameter is less than 6.0 mm. The proposed optimized method for effective aspherical operation with the Russian excimer laser device «Microscan-Vi-zum», the result of which would be formation of manageable planar wave front, effective functional optical zone with monofocal-ity on the entire surface and the absence of multifocality effect on the periphery of the optical zone, needs additional software, in which all of the above mentioned features of aspherical operation will be taken into account.