For many years, IOL power calculations in post-laser refractive surgery have always been a challenge. There have been many formulas and methods published by various authors, including ourselves, describing ways to improve the outcomes in these patients. It is encouraging to note that the outcomes and consistencies have been steadily improving over the years. From less than 50% within half a diopter of postoperative prediction error, this is now better than 70%. The methods are becoming more predictable and getting better integrated. In the past, we found that the Barrett True-K, with and without history, was among the best-performing method (Figure 1). Shammas PL was good too. In our recent study, we found that the Barrett True-K and EVO formulas, especially with TK, performed better than most others (Figure 2), published in Eye, August 2020 (https://doi.org/10.1038/ s41433-020-01159-5). TK is not the actual total corneal power but a Zeiss-modified total corneal power, available in IOLMaster 700. It is being modified to harmonize the IOL constants, without any adjustments, with the fundamental formulas, yet accommodating the effect of the posterior cornea on the total corneal power. The trend of our studies is similar to Ferguson TJ. We find that Barrett True-K and EVO (post LASIK) are good performers. Barrett True-K is now included in most modern biometers. Importantly, that streamlines and reduces the risk of transcription error from manually transcribing on online calculators. The availability of TK further enhances the outcomes for Barrett True-K, EVO, and Haigis, too. Barrett True-K and Haigis with TK are now available in IOLMaster 700. Unfortunately, the toric version of Barrett True-K is still not available in IOLMaster 700. There is still a need to do online calculations for the toric intraocular lens. Thankfully, the online toric version of both the Barrett True-K and EVO (post-LASIK) have been optimized for the optional TK values. Nonetheless, the integrated Barrett True-K provides a good spherical-equivalent reaffirmation to the online calculations, thus reducing the risk of transcription error. Post LASIK calculation was inconsistent. The use of multiple formulas reduced the risk of spurious outliers. The analysis of outliers by Ferguson Fam Han Bor, MD Senior Consultant, Tan Tock Seng Hospital 11 Jalan Tan Tock Seng, Singapore famhb@singnet.com.sg ASIA-PACIFIC PERSPECTIVES Figure 1. Fam HB., IOL calculation after refractive surgery: A South-East Asian experience, ESCRS 2016. Figure 2. Fam HB, Cataract surgery and lens selection for patients with previous refractive surgery, ESCRS 2021. TJ is important in reassuring and reducing the need for relying on multiple formulas. We are now getting more confident with cataract outcomes in patients with post-laser refractive surgeries. Editors’ note: Dr. Fam is a consultant for Johnson & Johnson Vision and Carl Zeiss Meditec. EWAP MARCH 2023 44 NEWS & OPINION
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