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56 | EYEWORLD | JUNE 2019 C ORNEA PRESENTATION SPOTLIGHT by Stefanie Petrou Binder, MD EyeWorld Contributing Writer error that would have resulted had the surgeon's preoperative plan been followed. He collected postoperative data from the ORA System (Alcon) from multiple centers in the U.S. The ORA Analyzor database stores pa- tient preoperative, intraoperative, and postoper- ative data on a secure server. The database had more than 1 million cataract surgeries recorded, roughly 300,000 of which included postop- erative data. Of those, 35,766 entries had the specified inclusion criteria, 1,786 of which had axial lengths over 26.5 mm and a single-piece acrylic IOL platform. Dr. Breen hypothesized that the absolute prediction error would be lower with IA and the proportion of eyes with postoperative abso- lute prediction error ≤0.50 D of the predicted postoperative SE would be higher with IA com- pared to the preoperative plan. Ten percent of the eyes were randomly selected for hypothesis development and 90% were used for hypothesis confirmatory analysis. None of the eyes had a history of surgery, prior refractive surgery, or ocular disease. IA calculations were driven by the measured apha- kic spherical equivalent (SE). "The calculation we did for prediction error was fairly basic," Dr. Breen said. "It was the IA predicted postoperative SE minus the actual postoperative SE. The absolute prediction error for the preoperative calculation was the differ- ence between the power implanted and the IOL power based on the preoperative calculation, actual postoperative SE, and the back-calculated postoperative SE prediction error had the pre- operative IOL power been implanted," he said. The results showed that both the mean and median preoperative prediction errors were sig- nificantly greater than the IA prediction error. "There were significant differences in both PEs, that is the mean absolute and the median abso- lute PE, not in all the cases but especially in the cases where there was a difference in lens power that was calculated by IA compared to the pre- operative, comprising about 51% of the cases," Dr. Breen said. "These differences in prediction A study involving nearly 2,000 eyes suggests that calculations incorporat- ing intraoperative aberrometry (IA) outperform preoperative calcula- tions, with the difference even more pronounced when IA suggested a different IOL power from preopera- tive measurements. Evolving beyond formulae The evolution of IOL power calculations has resulted in improved, more reliable refractive outcomes in cataract surgery. But achieving the predicted postoperative spherical equivalent is still difficult in a high percentage of eyes, with just over half of eyes demonstrating a residual refractive cylinder of ≤0.50 D, according to one study, 1 only 55% of cases reaching actual em- metropia according to another study, 2 and long axial lengths presenting a continued challenge to obtain target outcomes. 3 Intraoperative aberrometry, through its use of an aphakic refraction-based calculation, has been shown to help improve refractive out- comes in cataract surgery, according to Michael Breen, OD, who spoke at the 36th Congress of the European Society of Cataract and Refrac- tive Surgeons. While IA has shown encouraging outcomes, he said extensive data is lacking on how it could improve refractive outcomes in long eyes. IA in patients with bilateral cataracts un- dergoing toric IOL implantation increased the proportion of eyes with postoperative refractive astigmatism of 0.50 D or less and reduced the mean postoperative refractive astigmatism at 1 month, compared to standard methods, accord- ing to a study. 4 An unrelated study found 67% of eyes with prior myopic LASIK or PRK came within ±0.5 D of IA's predicted outcome, com- pared to 46% with conventional preoperative methodology. 5 Assessing IA In a retrospective analysis, Dr. Breen looked for differences between the absolute prediction er- ror using an IA driven calculation for IOL pow- er determination and the absolute prediction IOL power calculations incorporating intraoperative aberrometry About the doctor Michael Breen, OD Head, Medical Science, Surgical and Vision Care North America Clinical Develop- ment and Medical Affairs Alcon References 1. Holland E, et al. The AcrySof Toric intraocular lens in subjects with cataracts and corneal astigmatism: a randomized, subject-masked, parallel-group, 1-year study. Ophthalmology. 2010;117:2104–11. 2. Behndig A, et al. Aiming for emmetropia after cataract sur- gery: Swedish National Cataract Register study. J Cataract Refract Surg. 2012;38:1181–6. 3. Wang L, et al. Optimizing in- traocular lens power calculations in eyes with axial lengths above 25.0 mm. J Cataract Refract Surg. 2011;37:2018–27. 4. Woodcock MG, et al. Intra- operative aberrometry versus standard preoperative biometry and a toric IOL calculator for bilat- eral toric IOL implantation with a femtosecond laser: One-month results. J Cataract Refract Surg. 2016;42:817–25. 5. Ianchulev T, et al. Intraop- erative refractive biometry for predicting intraocular lens power calculation after prior myopic refractive surgery. Ophthalmology. 2014;121:56–60. continued on page 58

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