Eyeworld

48 | EYEWORLD | FALL 2024 R EFRACTIVE by Ellen Stodola Editorial Co-Director About the sources Avi Wallerstein, MD Executive Vice President Co-National Medical Director LASIK MD Montreal, Canada Mathieu Gauvin, PhD Director of Research & Development LASIK MD Montreal, Canada RESEARCH HIGHLIGHT I n a recent study, Avi Wallerstein, MD, Mathieu Gauvin, PhD, and colleagues explored the influence of angle kappa on multifocal IOL outcomes. 1 Dr. Wallerstein and Dr. Gauvin shared with EyeWorld the motivation behind this study, what was discov- ered, and what this means for future research. "Our lab, the McGill Refractive Surgery Research Unit, leverages large databases to investigate controversies in refractive surgery. With more than 100,000 new eyes added yearly, we utilize big data analytics to gain insights to improve patient care, dispel misinformation, and address unresolved questions in our field," Dr. Wallerstein and Dr. Gauvin said in an email to EyeWorld. The ongoing debate around angle kappa's impact on multifocal IOL (MIOL) outcomes caught the attention of these researchers due to its potential to affect large numbers of MIOL surgeries worldwide. The literature is divided: Some studies suggest that a large angle kappa might negatively impact postoperative MIOL outcomes, while others find no significant correlation. Additionally, some surgeons reject high angle kappa patients, while others are convinced that angle kappa or an attempt at IOL centration on the corneal vertex does not play a clinically significant role. Given the lack of consensus and the small sample sizes of pre- vious studies, Dr. Wallerstein, Dr. Gauvin, and colleagues saw an opportunity to bring clarity to this issue with a large-scale investigation. "Our goal was to conduct a robust, evi- dence-based study that would provide definitive answers and clarify the true impact of angle kappa on MIOL refractive outcomes and patient satisfaction, thereby guiding clinical decision making. As per all our investigations, we main- tained a neutral stance, understanding the need for a large-scale unbiased study," they said. According to Dr. Wallerstein and Dr. Gauvin, their study is the largest of its kind, involving a comprehensive review of 26,470 eyes from 13,235 patients across 21 Canadian IOL sur- gery centers. Conducting a study on this scale required meticulous data collection enabled by a custom EMR designed with research capa- bilities. They described the methodology of a thorough EMR review focusing on preoperative angle kappa measurements and standard re- fractive and subjective postoperative outcomes. "We assessed postoperative refractive accuracy (sphere, cylinder, spherical equivalent, defocus equivalent), visual acuity, and postoperative patient satisfaction—near, intermediate, and distance vision, and likelihood of recommend- ing the procedure," they said. "To ensure the accuracy and reliability of our findings, we implemented rigorous data validation processes," they continued. Outlier angle kappa values—those beyond three stan- dard deviations from the mean—were excluded from the analysis. Extreme values exceeding 2.5 standard deviations were reviewed by two expert eyecare professionals to verify accuracy, with any erroneous data points being manually discarded. "This meticulous approach allowed us to maintain a robust dataset, providing a highly reliable and comprehensive analysis of angle kappa's impact on MIOL outcomes." The study sought to characterize angle kappa and explore its relationship with postop- erative refractive accuracy, visual outcomes, and patient satisfaction in a large population of eyes with MIOLs. "It's crucial to thoroughly understand and characterize angle kappa in studies because not all measurements of angle kappa are equiva- lent," they explained. "In our study, we used the kappa displacement distance (DD), which measures the distance between the pupillary axis intercept on the cornea and the vertex normal, a point that closely corresponds to the visual axis. This measurement is known to be more accurate than the chord mu used in other studies, though the chord mu is a reasonable approximation." Chord mu measures the distance between the center of the entrance pupil and the sub- ject-fixated coaxially sighted corneal light reflex. While these measures are often used interchangeably, they are not identical. "Kappa DD values are generally larger than chord mu. Both measures are valuable for estimating angle kappa, but the distinction ensures consistency and accuracy in research." The study findings revealed that nearly all eyes undergoing refractive lens exchange or cataract surgery have some level of angle kappa Angle kappa and its influence on multifocal IOL outcomes

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