Eyeworld

EW FEATURE 46 All about IOL calculations • January 2017 AT A GLANCE • Getting within ±0.5 D of target refraction is the goal, but there are still many surgeons not reaching that in their IOL calculations. • Personalizing or optimizing one's lens constant improves accuracy of calculations. • Using an optical biometer instead of a contact A-scan can improve measurements for better calculations as well. • Avoid using drops or measuring IOP before performing keratometry as this can lead to variability in measurements. by Liz Hillman EyeWorld Staff Writer own formula, the Hoffer Q. In eyes 24.5 to 26 mm, Dr. Hoffer said he thinks the Holladay 1 is best, while in eyes greater than 26 mm, he said the SRK/T seems to work well. For eyes between 22 and 24.5 mm, Dr. Hoffer thinks the Holladay 1 and Hoffer Q are on par with each other. The Haigis formula, Dr. Hoffer said, includes triple personalization of three different lens constants (a0, a1, and a2). Dr. Hoffer said this optimization with data from at least 100 eyes should be done by Wolfgang Haigis, PhD, Wurzburg, Germany, through his website and not through others who purport to do it on the internet. "Then you're dealing with an extremely accurate formula in al- most all ranges—short eyes, medium eyes, and long eyes," he said, noting that it replaces the K with the preop ACD to predict ELP. Dr. Hoffer acknowledged other formulas—the Olsen, Holladay 2, which he said he wouldn't recom- mend, and the Barrett Universal II. He also mentioned the new Hoffer H-5, which takes into account the effect of gender and race on IOL power calculations. Dr. Hoffer said a soon-to-be-published study, which included 10,000 eyes—2,770 of which were within a quarter diopter of prediction—looked at the median absolute error (MedAE) of the Hoffer Q, Holladay 1, SRK/T, and the Hoffer H-5 and found the latter had the lowest MedAE, being 30–40% more accurate. Dr. Holladay said he would recommend recent formulas like the Holladay 2, Olsen 2, and Barrett Universal II. Older formulas, he said, are less accurate. He also recom- mended taking between five and seven measurements of the eye to predict the effective lens position. Dr. Hoffer noted that the Olsen 2 and Barrett are relatively recent, but the Holladay 2 is now celebrating its 20th birthday. A study of more than 3,000 eyes published in the Journal of Cataract & Refractive Surgery in 2016 com- pared seven IOL power formulas. 2 IOLMaster 500 and optimized lens constants were used, and other measures were taken to reduce vari- ability. Of the formulas tested—the Barrett Universal II, Haigis, Hoffer Q, Holladay 1, Holladay 2, SRK/T, and T2—the Barrett Universal II was the biggest mistake you can make," Dr. Hoffer said, adding that if you don't have an optical biometer and must use ultrasound for this measure- ment, do an immersion rather than an applanation. With several optical biometers on the market, do any stand out? Dr. Hoffer said he has compared a variety of machines, including the LENSTAR (Haag-Streit, Köniz, Swit- zerland), IOLMaster 500 and 700 (Carl Zeiss Meditec, Jena, Germany), Aladdin (Topcon Medical Systems, Oakland, New Jersey), and AL-Scan (Nidek, Fremont, California). "They're all good. You can't go wrong with any of these optical biometers, and I'm probably one of the few people who has done hands- on comparisons and published the results," Dr. Hoffer said. Dr. Holladay agreed that new- er optical biometers are equally accurate and noted that they have measures like standard deviations and signal-to-noise ratios to confirm the validity of the measurement. In addition to this advice, Dr. Holladay said cataract surgeons should not use any drops or measure IOP before performing keratometry. "It changes the Ks and leads to variability in measurements," he said. Dr. Hoffer personally advised against using what he called the outdated and error-prone regression formulas like the SRK 1 or SRK 2. Between these two surgeons, the jury is still out on some of the favored formulas. In short eyes (those less than 22 mm), Dr. Hoffer said he prefers his prove dramatically," Dr. Hoffer said. "Dr. Holladay and I were in a session [at a meeting] and he asked how many people personalize, and there were only two or three hands raised out of 50 to 70 people." Dr. Hoffer gave an example of how optimizing one's lens constant could affect patient outcomes. Let's say you're using the Hoffer Q for- mula and start out with a personal anterior chamber depth (pACD) of 5.55. After conducting 100 cases, inputting the implanted IOL lens power and the patient's postop re- fraction into your optical biometer, it calculates the ideal anterior cham- ber depth for each patient. Taking an average of what they should have been, now the optical biometer is predicting that your pACD is 5.63. "Now you're going to be using a more accurate pACD for the way you do surgery," Dr. Hoffer said. At the same time, the calculations were also done for the surgeon factor (SF) for the Holladay 1 formula and the A constant for the SRK/T formula. If personalizing in this way can improve lens power calculation accuracy so much, why don't more surgeons do it? Dr. Hoffer said it's a matter of being consistent with your IOL selection and making a habit of going back 1 to 3 months postop to input the patient's IOL power and refraction data. He added that some surgeons are not convinced of the importance of personalizing. Dr. Hoffer also recommended avoiding contact A-scan to deter- mine the length of the eye. "Using a contact A-scan is the Experts provide their thoughts on how to get as close to target as possible "T he measure of how good a surgeon is at selecting the correct IOL power is what percentage of cases are within ±0.5 D of the target," said Jack Holladay, MD, clinical profes- sor of ophthalmology, Baylor College of Medicine, Houston. And yet, research has shown that many surgeons are not achiev- ing that goal. Data analysis from Massachusetts Eye and Ear Infirmary published in 2014, for example, showed that out of 1,275 surgeries, 67% were within ±0.5 D of the target refraction; 94% were within ±1 D. 1 Dr. Holladay said an "A sur- geon" gets within ±0.5 D 90% of the time, which he thinks is less than 1% of surgeons. B surgeons—about 20% of today's surgeons—get 80 to 90% of their cases within ±0.5 D, Dr. Holladay said. So how can an ophthalmolo- gist improve the accuracy of his or her IOL calculations? The first tip recommended by Dr. Holladay and Kenneth J. Hoffer, MD, clinical pro- fessor of ophthalmology, Stein Eye Institute, University of California, Los Angeles, is to personalize their lens constants. "To be an A or B surgeon, you must personalize your lens constant by putting postop refractions into a software package," Dr. Holladay said. "Most doctors don't personalize; if they did, their results would im- Perfecting IOL power predictions

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