Pearls for Calculating IOL Power

There were plenty of pearls this year at the recent annual meeting of the American Society of Cataract and Refractive Surgery (ASCRS 2022). Enough that if they were the real thing, we could provide plenty of free cataract surgeries to those in need around the world — the exact number depends on which part of the Earth’s circulatory system they come from, this writer just discovered. But just like real pearls, these pearls of wisdom hold their value. But unlike real pearls, they’re ready to be passed down to the next generation now. No need to wait for your grandmother to have a bout of generosity. 

Today, we present to you a talk by Dr. Helga Sandoval, the director of clinical research at US Eye and an affiliate faculty member of the Ophthalmology-Medical University of South Carolina in Charleston. The presentation was called My Top 5 Pearls for Calculating IOL Power. On a side-note, have a bonus pearl: I highly recommend Charleston if you need a quick weekend getaway. 

She started her talk by noting that to her, “calculating IOLs is like an art. It’s not like one size fits all. Every patient is different and they want different things.” Dr. Sandoval is a particularly great artist in the world of IOLs, and her practice has been said to have the highest refractive accuracy in the world.

Pearl #1: Ocular Surface Optimization

Dr. Sandoval says that ocular surface optimization “is the key to for a good measurement prior to the surgery” and the appropriate management before the biometry is “key to improve the outcomes as well as patient satisfaction.” The keys to having a healthy ocular surface are pre-op optimization, surface protection during surgery, and quality post-op treatment. 

Pearl #2: Validation Criteria

She cited the recent guidelines for IOLMaster (Zeiss) and Lenstar (Haag Streit) measurements of Dr. Warren Hill, the long-serving medical director of East Valley Ophthalmology in Mesa in Arizona. Dr. Hill proposed many guidelines that are followed, but there are quite a few and Dr. Sandoval highlights the four most common. 

The difference in the axial length should be consistent between both eyes, the Lenstar being 0.3 and the IOLMaster being 0.33. “And if there is a difference then we just confirm that difference,” she said.

Next, we have the K readings. Consistency between the K1 and K2 should be within a quarter diopter with both the IOLMaster and Lenstar. The K power should also be 1.2 in the IOLMaster and 0.9 in the Lenstar: “The difference between the mean case between the two eyes.”

Use both the Lenstar and IOLMaster to confirm the results, making sure measurements are performed correctly and the axis is correct. Compare multiple results before proceeding. She said, “if you do the test and it matches, proceed. If they don’t match repeat, but you have to repeat after the surface has been treated.” Don’t just repeat immediately, wait a week or two to make the differences pop.

Pearl #3: IOL Calculation Formulas

Dr. Sandoval noted that “it’s key to use more formulas to get better outcomes.” There are a lot of formulas out there and be sure to find what feels good to you. A lot of them are online calculators so it’s very important that you are careful not to enter what Dr. Sandoval — and our editors — call “typos” or your results could be way off. 

Modern formulas that the presentation lists are Barret Universal II, Kane and Ladas. Other formulas and calculators include Emmetropia Verifying Optical (EVO), Nallasamay, Hoffer QST, PEARL-DGS, K6 and VRF.

Pearl #4: A-Constant Optimization

Dr. Sandoval and her team compared post-op information prior to optimization. They started with patients who were around -0.4, and were closer to planar after optimization. They found that the “number of patients within a half-diopter improved from 64 to 90% and 100% within 1 diopter.”

Pearl #5: Cataract Surgery Planning Software

With new software you can skip data entry and simply use the formulas that are listed and compare to check for a difference. But don’t be lazy. Don’t depend on it. She said: “This is just a tool. This is not going to tell you what to do.” As with anything else, perform your own analysis and decide what will work the best for you and your patients.   

Editor’s Note: ASCRS 2022 was held on April 22-26, as a physical show in Washington DC, USA. Reporting for this story took place during the event.

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