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  • Cataract/Anterior Segment

    This prospective case series compares the efficacy of a computer-assisted system versus manual marking for toric IOL alignment.

    Study design

    The randomized study included 57 eyes of 29 patients with regular corneal astigmatism (1.25 D or higher) who were treated by a single surgeon. Twenty-nine eyes received digital marking with the Callisto Eye System (Carl Zeiss Meditec AG), and 28 eyes were manually marked before surgery using a bubble marker to denote the 0-degree axis while the patient was upright. Patients were evaluated 3 months after surgery. 


    On average, toric misalignment was significantly lower in the digital group (2.0 ± 1.86 degrees) than the manual group (3.4 ± 2.37 degrees; P=0.026). In addition, the mean deviation from the predicted target-induced astigmatism was also significantly lower in the digital group than the manual group (0.10 vs. 0.22 D; P=0.08). Despite these findings, uncorrected distance visual acuity did not differ between groups.

    In contrast to other comparisons of marking techniques, this study also addressed the amount of surgical time required to perform the two techniques. Alignment time was significantly reduced in the digital group (37.2 vs. 59.4 seconds), resulting in an overall shorter surgical time (727.2 digital vs. 1110.0 seconds manual).


    This study did not evaluate other marking systems such as digital photography, which uses iris fingerprinting software. A cost comparison of the methods might have proven useful, given the current era of rising healthcare costs. Weighing the overall benefits of the Callisto Eye System (i.e., accounting for the increased clinical measurement time versus the reduced operating time) is recommended.

    Clinical significance

    The findings suggest that this digital tracking approach for toric IOL alignment is an efficient and safe way to improve refractive outcomes. Furthermore, the Callisto software may help to streamline the surgical workflow.