34 EyeWorld Asia-Pacific | December 2024 REFRACTIVE SURGERY About the Physicians Avi Wallerstein, MD | Executive Vice President, Co-National Medical Director, LASIK MD, Montreal, Canada | awallerstein@lasikmd.com Mathieu Gauvin, PhD | Director of Research & Development, LASIK MD, Montreal, Canada | mgauvin@lasikmd.com Relevant Disclosures Wallerstein: None Gauvin: None Reference 1. Wallerstein A, et al. Angle kappa influence on multifocal IOL outcomes. J Refract Surg. 2023;39:840–849. This article originally appeared in the September 2024 issue of EyeWorld. It has been slightly modified and appears here with permission from the ASCRS Ophthalmic Services Corp. ASIA-PACIFIC PERSPECTIVES Michael Lawless, MD Clinical Associate Professor Sydney, Australia, 4/270 Victoria Ave, Chatswood, NSW Australia michael.lawless@vei.com.au Drs Wallerstein and Gauvin should be congratulated for their 2023 paper regarding the influence of angle kappa on multifocal intraocular lens outcomes. As they note, it is a controversial issue. They had a large database of 26,470 eyes from 13,235 patients across 21 Canadian IOL surgical centers. Approximately one-third of these patients filled in the patient satisfaction questionnaire. This paper provides valuable new evidence pushing the pendulum away from angle kappa as a relevant metric in IOL selection. The authors used the kappa displacement distance (DD), that is the distance between the pupillary axis intercept on the cornea and the vertex normal. The vertex normal corresponds reasonably well to the visual axis. The authors state that the kappa DD is known to be more accurate than chord mu. That is debatable. The authors used the Orbscan device to measure the kappa DD. Most devices including IOL Master 700, Galilei, Pentacam and Sirius, to choose some examples, use chord mu. Chord mu is known to be a lower number than kappa DD. So if you’re used to looking at chord mu, the numbers in this paper will be larger and this is reflected in the fact that 67% of eyes had a kappa DD greater than 0.5mm. Unfortunately halo and glare were not directly assessed, and so the authors used patient satisfaction as a proxy for this. Their patient satisfaction questionnaire was not validated. A validated questionnaire is a reliable instrument, but a non-validated questionnaire is not. The authors did not compare their kappa DD in mesopic versus photopic conditions. This is important because the arguments around the relevance of angle kappa in lens selection and how patients respond to, for example, trifocal lenses in this setting, is a subtle issue. More important issues in multifocal selection and tolerance are the quality of the ocular surface, the health of the macula, whether PCO exists post-op and in particular the corneal optics. By that I mean some measure of the corneal irregularity index or corneal high order aberration profile preoperatively. These are more important metrics than the angle kappa number. So to tease out the relevance of angle kappa needs more sophisticated analysis and while this paper is a large series and provides useful information, it does not settle the question of whether a high angle kappa is relevant for trifocal lens exclusion, or if there is a large angle kappa, whether patients will have more subjective halos and glare postoperatively. This paper should make us put less weight on angle kappa when considering multifocal IOL selection, but as the authors rightly state, other things are more important. As we refine and try to get the best from complex intraocular lenses, we need studies like this, and studies which go into more detail about visual quality and the final position of the intraocular lens before we can say that angle kappa is a relevant or irrelevant metric in lens surgery. This valuable paper in my view highlights the lack of data and knowledge around eventual IOL position and the impact this has, rather than providing absolute confirmation of the impact of angle kappa. Editors’ note: Dr. Michael Lawless is a consultant for Carl Zeiss and Alcon, but has no relevant financial interests related to the comments.
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