FEATURE EWAP JUNE 2022 7 by Liz Hillman Editorial Co-Director IOL power misses: Why, what, and how A n IOL power miss — is it a complication or not? The answer is nuanced. Some patients experience residual refractive error that is relatively significant and are still happy with their outcome, while others with a seemingly small residual refractive error are unhappy. David Salz, MD, and H. John Shammas, MD, discussed why IOL power misses occur, what the options are for corrective action, and how to avoid such misses in the first place. Dr. Shammas said an error in IOL power calculation is usually suspected when a patient presents postop with unexpected, induced myopia, hyperopia, or aniseikonia. ºWhen we first started using IOLs after cataract extraction 40 years ago, results within This article originally appeared in the April 2022 issue of EyeWorld. It has been slightly modified and appears here with permission from the ASCRS Ophthalmic Services Corp. ±2 D were acceptable and deemed superior to any aphakic correction. With the refinement of IOL formulas, patients and surgeons are now expecting a more accurate final refraction in the operated eye. Nowadays, 80% of our patients are expected to be within 0.50 D and 100% within 1 D,” he said. However, Dr. Shammas noted that some patients with 1 D of error are happy with their results while patients with error as low as 0.5 D can be unhappy. “It boils down to patient expectations,” he said. Dr. Salz said that even patients off by as little as a quarter of a diopter can be unhappy if they are very sensitive about their vision. “The misses we dwell on more are when patients are unhappy, though obviously we try to minimize any amount of error period,” he said. Why misses occur Dr. Salz said there is variability within different formulas that can be used to calculate IOL power. “The reality is there is a margin of error for surgery with IOL calculations even with all the technology we now have,” he said. Another source of variability is effective lens position. Formulas can try to predict effective lens position, but they’re not perfect, Dr. Salz said. The number one source of error leading to IOL power misses, Dr. Salz said, occurs with biometry. “Most physicians have some kind of optical biometry that they use, so most variability is with the corneal measurements, the steepness of the cornea. If those numbers are off a little bit — someone has dry eye, for example — the measurements of the cornea could be off because that’s one of the main things that goes into these calculations,” he said. Dr. Shammas said most studies show that almost no errors occur over 1 D, but he still oc-casionally sees a referral with an error between 2 D and 5 D, resulting in myopia or hyperopia in the operated eye. “Occasionally, we see the inadvertent use of a different Contact information Salz: dasalz@gmail.com Shammas: hshammas@aol.com
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