Refractive: Research highlight
Fall 2024
by Ellen Stodola
Editorial Co-Director
In 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 discovered, and what this means for future research.
“Eyes with a large angle kappa should not be excluded from MIOL surgery, nor should angle kappa be used as a sole determinant for MIOL candidacy.”
Avi Wallerstein, MD, and Mathieu Gauvin, PhD
“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 previous 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, evidence-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 maintained 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 surgery centers. Conducting a study on this scale required meticulous data collection enabled by a custom EMR designed with research capabilities. They described the methodology of a thorough EMR review focusing on preoperative angle kappa measurements and standard refractive 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 recommending the procedure,” they said.
Source: Mathieu Gauvin, PhD
“To ensure the accuracy and reliability of our findings, we implemented rigorous data validation processes,” they continued. Outlier angle kappa values—those beyond three standard 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 postoperative 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 equivalent,” 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 subject-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 preoperatively, with 72% having an RMS angle kappa 0.5 mm or greater and 12% greater than 1.00 mm.
The analysis showed that angle kappa does not correlate to postoperative refractive accuracy, vision, subjective satisfaction, or the likelihood of recommending the procedure to friends and relatives. The contribution of angle kappa to clinical outcomes in most eyes undergoing refractive lens exchange and cataract surgery was negligible in this large-scale study.
“Eyes with a large angle kappa should not be excluded from MIOL surgery, nor should angle kappa be used as a sole determinant for MIOL candidacy,” Dr. Wallerstein and Dr. Gauvin said.
Some surgeons use the criterion of an angle kappa DD greater than 0.5 mm to exclude patients from surgery. “Had we used those criteria, our analysis reveals that 67% of the eyes in the current study—who had excellent outcomes—would have been excluded from undergoing MIOL surgery, leaving only one-third of patients as candidates,” they said.
While the evidence is strong that angle kappa cannot be used as a single variable to determine MIOL candidacy, they emphasized that the study does not suggest that angle kappa is totally without significance in a comprehensive preoperative assessment.
“Angle kappa should be considered alongside other factors such as axial length, corneal topography, corneal higher order aberrations and astigmatism, retinal health, pupil size, and the patient’s specific visual needs and lifestyle. This multi-variable approach ensures more accurate surgical planning and better overall prediction of outcomes. While angle kappa alone does not show evidence as being a critical factor, it should continue to be measured and combined with other diagnostic data to optimize MIOL outcomes.”
Dr. Wallerstein and Dr. Gauvin plan to extend their research by exploring additional variables that might influence MIOL outcomes, such as preoperative pupil size, which appears to be more predictive than angle kappa in their preliminary assessment. “In addition, machine learning will undoubtedly enhance our ability to predict patient satisfaction and refractive outcomes by analyzing multiple variables simultaneously, paving the way for even more personalized and effective treatments,” they said
Further studies could include longer follow-up periods to assess the stability of MIOL centration and its long-term impact on visual quality. “Additionally, investigating other measures of visual quality, such as contrast sensitivity and higher order aberrations, could provide deeper insights. We’re also interested in examining patient-reported visual disturbances, such as halos and glare, in relation to angle kappa. This expanded research will help refine our understanding and further improve surgical outcomes for patients.”
Dr. Wallerstein and Dr. Gauvin concluded by emphasizing that eyes with a large angle kappa should not be excluded from MIOL surgery, nor should angle kappa be used independently for determining MIOL candidacy. They also highlighted the importance of large-scale, data-driven research in resolving clinical debates and advancing ophthalmic practice. “We hope that our findings will encourage surgeons to adopt a more comprehensive approach to MIOL candidacy and thoroughly analyze their outcomes, ensuring that decisions are based on robust evidence rather than isolated variables. Ultimately, our goal is to improve patient outcomes and satisfaction in laser vision correction and IOL surgery, fostering a better quality of life for those undergoing these procedures.”
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
Reference
- Wallerstein A, et al. Angle kappa influence on multifocal IOL outcomes. J Refract Surg. 2023;39:840–849.
Relevant disclosures
Wallerstein: None
Gauvin: None
Contact
Wallerstein: awallerstein@lasikmd.com
Gauvin: mgauvin@lasikmd.com
