Cyclorotation in astigmatic correction

Femto laser’s automated measurement system reliable and accurate

Cheryl Guttman Krader

Posted: Thursday, December 3, 2020

Douglas D Koch, MD

A computer-based method for automated measurement of cyclorotation incorporated in the Catalys Precision Laser System (Johnson & Johnson Surgical Vision) demonstrated a high rate of successful registration and accuracy when compared to cyclorotation determinations of human graders, according to research presented at ARVO 2020.
The laser’s algorithm for measuring cyclorotation registers the image of the preoperative undilated iris captured by the Cassini low-light topographer (Cassini Technologies, Inc.) with the patient sitting upright to the dilated iris imaged with the patient supine and with the eye docked with the Catalys’s liquid optics interface. In addition to calculating the angle of cyclorotation, the algorithm generates a quality score indicating the confidence of the returned angle’s accuracy.
An investigation of the system’s performance was conducted using images from 49 eyes of cataract patients operated on at Baylor College of Medicine, Texas, USA (37 eyes) and the Eye Centre of New York, New York, USA (12 eyes). The results showed that the automated algorithm successfully registered image pairs for 47 (96%) of the 49 eyes. For 46 (98%) of the 47 registered eyes, the cyclorotation measurement calculated by the automated system was within 2 degrees of the average cyclorotation determined by three human graders.
Discussing the relevance of the findings with EuroTimes, Douglas D Koch, MD, Baylor College of Medicine, noted that his goal for astigmatic correction during cataract surgery is to reduce refractive astigmatism to less than 0.5D.
“This is especially important for patients receiving presbyopia-correcting IOLs. When using the femtosecond laser to make arcuate incisions or toric alignment marks, accurate registration is essential to achieving these outcomes, but it can be complicated by rotation of the eye between the preoperative measurement and the laser,” he said.
“Manual marking techniques to guide astigmatic correction are time-consuming and subject to error if not meticulously performed. Automated intraoperative registration by the femtosecond laser provides maximal accuracy and saves time by eliminating preoperative and intraoperative marking steps.”
A second objective of the study was to describe the amount of cyclorotation present in femtosecond laser cataract surgery, said David Dewey, Research Scientist, Johnson & Johnson Surgical Vision, who reported the research.
The analyses showed the range and distribution of measured cyclorotation was nearly identical for the human graders and automated algorithm and identified a difference of about 10º between left and right eyes.
Mr Dewey commented: “In order to cover the breadth of the distribution in a symmetric manner, the automated system needs to address a ±20º range of cyclorotation angles. Based on other research, the left-right eye difference is likely due to the docking induced portion of the measured cyclorotation and not the natural cyclorotation associated with change in patient position,” he said.