Eyeworld

44 | EYEWORLD | OCTOBER 2019 R EFRACTIVE YES CONNECT by Liz Hillman EyeWorld Senior Staff Writer How do you collect your postop outcomes data for later optimization analysis? What systems do you use? Dr. Shammas: You do not need any sys- tem. You have to record the power of the IOL used and the spherical equivalent of the final refraction. Dr. Holladay: The Holladay IOL Consultant software does this automatically when you enter the surgical and postoperative refraction. The optimization excludes outliers that are more than two standard deviations from the mean be- cause they are usually measurement errors and cases with less than 20/50 best-corrected vision because the refraction is suspect. The software does not actually use the personalized lens constant (PLC) until it reaches statistical signif- icance, which is usually from 30 to 50 cases. It looks at the data through a "rearview window," looking at the data that is most recent first and going back historically until statistical signifi- cance is reached. This keeps the PLC "fresh" in case the surgeon makes changes in his surgical technique that may unknowingly affect the PLC. What is your process of optimization of surgical outcomes derived from your col- lection of data? What is the process of how you go from a collection of postop out- comes data to optimization of your future IOL calculations? Dr. Shammas: There are different ways to do that. Some biometers will allow you to enter the power of the IOL used and the spherical equiv- alent of the final refraction and it will continu- ously optimize the constants being used. An easy way to do this optimization is to collect at least 50 cases (surgeons can start with 20 cases and update later). You then compare the final refraction to the one predicted by the formula. You subtract the predicted refraction from the obtained refraction and average all these differences. If the average difference is a negative value, that means that the surgeon is using a higher power IOL than what is required and he/she should decrease the A constant by Y ou've performed cataract surgery, implanted your selected IOL, and conducted postop visits. While it might sound like your job is done at this point, if you want to improve your outcomes further, now's the time to start crunching numbers. EyeWorld reached out to experts H. John Shammas, MD, and Jack T. Holladay, MD, to get their thoughts about systems for selecting IOLs and managing calculations, following up on refractive outcomes, and tips for conducting clinical research with IOL data. At what point postoperatively do you rec- ommend collecting variables for outcome analysis? What would you say are the most relevant variables to collect from each pa- tient? Dr. Shammas: After surgery, we refract the operated eye on day 1 and day 7. These early refractions will ensure that no errors in the IOL calculations have been made, [which] might re- quire immediate intervention. However, the best time to check the final outcome is 4 to 6 weeks after the surgery; this is when we prescribe glasses. If the surgeon or his/her staff want to conduct an outcome analysis, they would record the IOL power and the final refraction. Dr. Holladay: Six months after surgery is ideal for stability in the spherical equivalent refraction as well as the residual astigmatism. Although 3 months is often used, it is too soon for changes in the capsular bag to be complete and axial changes in the IOL are still occurring. FDA clinical trials have visits at 1 day, 1 month, 3 months, 6 months, and 1 year. The 6-month data is usually the visit where refraction is used for analysis. There is a long-term drift in against-the-rule astigmatism of about 0.25 D per decade that is the same for both cataract surgery and controls found by Ken Hayashi, MD, in his article following patients for 20 years. 1 Crunching numbers for IOL optimization About the doctors Jack T. Holladay, MD, MSEE, FACS Clinical professor of ophthalmology Baylor College of Medicine Houston H. John Shammas, MD Clinical professor of ophthalmology Keck School of Medicine, University of Southern California Los Angeles

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