Eyeworld

60 | EYEWORLD | APRIL 2022 by Liz Hillman Editorial Co-Director ATARACT C About the physicians David Salz, MD The Eye Specialists Bridgewater, New Jersey H. John Shammas, MD Shammas Eye Medical Center Lynwood, California References 1. Jivrajka RV, et al. Improving the second-eye refractive error in patients undergoing bilateral sequential cataract surgery. Ophthalmology. 2012;119:1097– 1101. 2. Covert DJ, et al. Intraocular lens power selection in the sec- ond eye of patients undergoing bilateral, sequential cataract extraction. Ophthalmology. 2010;117:49–54. Relevant disclosures Salz: None Shammas: Alcon, Oculus 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 be- cause 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 power IOL due to human error," he said, adding, "The most common cause is an error in axial length measurement. These errors are often seen in long or short eyes, especially if the eyes present with advanced cataracts that could not be measured by optical biometry; the technician will resort to measuring these eyes with ultrasound, with a greater possibility of error measurements." What options for 'treatment' First and foremost, Dr. Shammas said to identify the source of postoperative error. • Recheck the power of the IOL against the calculated power to rule out human error. Dr. Shammas recommended the surgeon personally check the IOL power prior to implantation. • Remeasure both eyes to rule out error in axial length measurement. • Recalculate corneal power to rule out postoperative steepening of the cornea. Dr. Shammas said tight sutures can occasional- ly cause steepening. • Assess the IOL's position to rule out forward placement with or without tilt. How to treat the eye with residual refrac- tive error depends on the patient's level of unhappiness, Dr. Salz said. If the refraction isn't perfect but the patient is happy with the overall quality of vision, Dr. Salz said there is no reason A n IOL power miss—is it a complica- tion or not? The answer is nuanced. Some patients experience residual refrac- tive 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 myo- pia, hyperopia, or aniseikonia. "When we first started using IOLs after cataract extraction 40 years ago, results within +/–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 pa- tients 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 differ- ent 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. IOL power misses: Why, what, and how

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