In most patients undergoing cataract surgery, emmetropia can be achieved by implantation of a monofocal intraocular lens (IOL). However, several studies have shown that approximately 20% to 30% of patients who undergo cataract surgery have a preexisting corneal astigmatism of 1.25 diopters (D) while the prevalence of corneal astigmatism >2.00 D is 8% and over >3.00 D 2.6%. This astigmatism, if not corrected during surgery, leads to postoperative spectacle dependence. In patients without contraindications and a desire to achieve postoperative freedom from spectacles for distance vision, correction of astigmatism can be achieved at the time of surgery by using toric IOLs.~A number of factors relating to corneal astigmatism are critical to lens selection and positioning.The most important factors are the preoperative corneal measurements and the correct alignment of the toric lens itself.~Each degree of deviation results in a 3% reduction in astigmatism correction. The introduction of digital marking systems is intended to minimize the disadvantages of manual marking, such as tilting of the head during marking, incorrect and smudged marking. In addition to several different manual marking methods, there is also a range of digital markers which have been proven to be equal or even better than manual marking. These include among others the Callisto Eye with Z-Align and the Alcon VERION Digital Marker. The principle of these digital marking systems is based on a preoperative photo which is recorded in the course of biometry where the keratometry values are obtained. In the further course, the steep axis is determined on the basis of this image and the target axis is projected on to the eye intraoperatively. Beside the ideal implantation axis for the T-IOL, the size of the capsulorhexis and position, as well as incision placement can be displayed.~In the course of this study, we will investigate the alignment axis of the two most used digital guidance systems from Alcon and Zeiss. A head to head comparison has already been carried out by Hura et al. in 2017.~15 eyes of 15 patients will be included into this study. There will only be one preoperative study visit, on the day of surgery, where reference pictures with a slitlamp camera and the biometers will be taken.
Comparison of the alignment axis of the Alcon Verion and the Zeiss Callisto alignment systems intraoperatively