A modified version of the FemtoLASIK technology for the correction of mixed astigmatism on the FemtoVisum and Microscan Visum

Introduction. The functional results after refractive surgery for astigmatism are influenced by the diameter and localization of the femtoflap, the expansion of the ablation zone, its correct centering, and the good functioning of the tracking system. Purpose of the study were to modify the course of femtolasic surgery in patients with mixed astigmatism using the FemtoVisum and Microscan Visum. Material and methods. A total of 32 people (50 eyes) with mixed astigmatism were examined. The average value of the cylindrical component was 3.87 ± 0.25 diopters (range 1.25 to 6.25 diopters). The mean thickness of the cornea in the center was 515 ± 5.12 μm (510 to 530 μm). All patients had a significant shift of the optical axis in relation to the center of the pupil and corneal thickness was lower than average. The first stage in the operation was the fixation of the visual axis and the launch of the tracking system on the MicroScanVizum, which gave a clear understanding in terms of further localization of the flap and ensuring the correct centering of ablation. After that, the stage of femtoflap formation was carried out with its positioning after aplanation on the cornea not in the center of the pupil, but taking into account the angle kappa. Results and discussion. In 42 % of cases, after femtodissection, the presence of a small accumulation of gas was noted, which did not interfere with ablation and the tracking system worked non-stop. Fixation of the visual axis and initiation of the tracking system to the stage of femtodissection provided more accurate centering of ablation, despite the change in the transparency of the stroma. By 12 months after surgery, the result is stable, repeated operations were not performed due to high visual functions. Conclusions. The results of mixed astigmatism correction on the Visum platforms according to the proposed algorithm are effective, safe, predictable and stable. The proposed operation option allows to personalize the positioning of the femtoflap and ensure the correct centering of the ablation, which reduces the risk of decentration and increases the functional results of the operation. Keywords: femtolasic, femtovisum, microscan visum, mixed astigmatism, ablation center, angle kappa, visual axis