Best IOL power calculation formula varies with atypical eyes
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BOSTON — Atypical eyes pose challenges for IOL calculations and require special treatment, according to a speaker at the American Society of Cataract and Refractive Surgery meeting.
In the Cornelius Binkhorst, MD, Lecture, Mitchell P. Weikert, MD, MS, ABO, said there are four primary sources of error in IOL power calculations: effective lens position, postoperative refraction, axial length and corneal power measurement.
“As formulas have evolved, developers have incorporated various strategies to get around or mitigate the effect of these sources of error, such as adding measurement variables, building ray-tracing models, incorporating big data and artificial intelligence, or a combination of these methods,” he said. “Unfortunately, all of the more modern formulas are essentially black boxes. So, we can study how they perform, but we really don’t have insight into their inner workings.”
Weikert discussed four common groups of atypical eyes: long eyes, short eyes, keratoconic eyes and post-laser vision correction eyes that underwent LASIK or PRK.
Long eyes have an axial length greater than about 25 mm and occur in up to 16% of patients undergoing cataract surgery, Weikert said. IOL power tends to be underestimated in these eyes, resulting in hyperopic errors.
Short eyes are less than about 22 mm in axial length and occur in up to 7% of cataract surgery patients. IOL power is usually overestimated, leading to myopic errors.
The prevalence of keratoconic eyes is about one in 2,000, and Weikert said these eyes are affected by variable measurements due to contact lens use. IOL power is commonly underestimated, leading to hyperopic errors.
Post-laser vision correction eyes are becoming more common and occur in up to 14% of cataract surgery patients at Weikert’s center. IOL power tends to be underestimated after myopic ablation and overestimated after hyperopic ablation.
Weikert said the best IOL power calculation formula varies depending on the kind of atypical eye.
“We all owe a debt of gratitude to the atypical individuals who really enjoy this stuff and have put so much blood, sweat and tears into this work to improve our results and our patients’ outcomes,” he said. “They’re a very special group of individuals who deserve a lot of recognition. So, if you see any of them out in the wild, please, thank a nerd.”
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Weikert MP. IOL calculations in atypical eyes: Exploration & explication. Presented at: American Society of Cataract and Refractive Surgery meeting; April 5-8, 2024; Boston.
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