35 EyeWorld Asia-Pacific | September 2024 Dr. Yeo’s study concluded that the EVO PK, EVO, Barrett True-K PK, and PEARL-DGS TK formulas were the most accurate. Utilizing TK or PK values improved the outcomes for all formulas. The legacy Haigis-L and Shammas-PL formulas resulted in the lowest accuracy with a myopic error tendency. “Always use measured PK from TK for post-LVC IOL calculations,” Dr. Yeo reminded the audience. Another aspect Dr. Yeo discussed was whether using measured posterior corneal astigmatism (PCA) is of any benefit in toric IOL calculations. In eyes with a measured PCA of 0.5 D or more, the Barrett toric calculator using measured PCA instead of predicted PCA provided more accurate IOL outcomes.12,13 In his own paper, Dr. Yeo found a benefit in using measured PCA for eyes with non-vertical PCA for both the Barrett and EVO formulas.14 Finally, in eyes with keratoconus, formulas using TK performed the best. “Results from studies showed that the Barrett True-K with PK did the best in both severe and non-severe keratoconus,” Dr. Yeo said. Additionally, “even though the EVO is not a keratoconus formula, it was reported that with TK, it actually works in non-severe keratoconus.” In summary, Dr. Yeo reiterated that TK really benefits IOL calculations in eyes with atypical corneas: post-LVC, toric IOL calculations where measured PCA is high or non-vertical, and keratoconus eyes. “In the past, it was much more challenging for us as surgeons because we had to do calculations manually,” Dr. Shetty commented. “But now, with the IOLMaster® 700, where you can get the actual measurement of the posterior cornea, life is becoming easier and easier.” The EVO PK, EVO, Barrett True-K PK, and PEARL-DGS TK formulas using total keratometry values perform with higher accuracy than the traditional legacy formulas. Not all products, services or offers are approved or offered in every market and approved labeling and instructions may vary from one country to another. The statements of the authors of this supplement reflect only their personal opinion and experience and do not necessarily reflect the opinion of Carl Zeiss Meditec AG or any institution with whom they are affiliated. Carl Zeiss Meditec AG has not necessarily access to clinical data backing the statements of the authors. The statements made by the authors may not yet been scientifically proven and may have to be proven and/or clarified in further clinical studies. Some information presented in this supplement may only be about the current state of clinical research and may not be part of the official product labeling and approved indications of the product. The authors alone are responsible for the content of this supplement and any potential resulting infringements resulting from, in particular, but not alone, copyright, trademark or other intellectual property right infringements as well as unfair competition claims. Carl Zeiss Meditec AG does not accept any responsibility or liability of its content. References: 1. Sekundo W, Reinstein DZ, Blum M. Improved lenticule shape for hyperopic femtosecond lenticule extraction (ReLEx FLEx): a pilot study. Lasers Med Sci. 2016 May;31(4):659-64. 2. Pradhan KR, Reinstein DZ, Carp GI, Archer TJ, Dhungana P. Small Incision Lenticule Extraction (SMILE) for Hyperopia: 12-Month Refractive and Visual Outcomes. J Refract Surg. 2019 Jul 1;35(7):442-450. 3. Reinstein DZ, Pradhan KR, Carp GI, Archer TJ, Gobbe M, Sekundo W, Khan R, Citron K, Dhungana P. Small Incision Lenticule Extraction (SMILE) for Hyperopia: Optical Zone Centration. J Refract Surg. 2017 Mar 1;33(3):150-156. 4. Reinstein DZ, Pradhan KR, Carp GI, Archer TJ, Gobbe M, Sekundo W, Khan R, Dhungana P. Small Incision Lenticule Extraction (SMILE) for Hyperopia: Optical Zone Diameter and Spherical Aberration Induction. J Refract Surg. 2017 Jun 1;33(6):370-376. 5. Fanney D, Layser GS, K AR, Kohlhammer S, Kübler C, Seibel BS. Experimental study comparing 2 different phacoemulsification systems with intraocular pressure control during steady-state flow and occlusion break surge events. J Cataract Refract Surg. 2023 Sep 1;49(9):976-981. 6. Srivannaboon S, Chirapapaisan C. Comparison of refractive outcomes using conventional keratometry or total keratometry for IOL power calculation in cataract surgery. Graefes Arch Clin Exp Ophthalmol. 2019;257(12):2677-2682. 7. Fabian E, Wehner W. Prediction Accuracy of Total Keratometry Compared to Standard Keratometry Using Different Intraocular Lens Power Formulas. J Refract Surg. 2019;35(6):362368. 8. Danjo Y, Ohji R, Maeno S. Lower refractive prediction accuracy of total keratometry using intraocular lens formulas loaded onto a swept-source optical biometer. Graefes Arch Clin Exp Ophthalmol. 2023;261(1):137-146. 9. Zhao H, Chen X, Liu B, Liu X, Liu Y. Accuracy of refractive outcomes using standard or total keratometry for intraocular lens power formulas in conventional cataract surgery. BMC Ophthalmol. 2023;23(1):346. 10. Lawless M, Jiang JY, Hodge C, Sutton G, Roberts TV, Barrett G. Total keratometry in intraocular lens power calculations in eyes with previous laser refractive surgery. Clin Exp Ophthalmol. 2020;48(6):749-756. 11. Anter AM, Bleeker AR, Shammas HJ, et al. Comparison of Legacy and New No-History IOL Power Calculation Formulas in Postmyopic Laser Vision Correction Eyes. Am J Ophthalmol. Published online March 20, 2024. 12. Reitblat O, Levy A, Megiddo Barnir E, Assia EI, Kleinmann G. Toric IOL Calculation in Eyes With High Posterior Corneal Astigmatism. J Refract Surg. 2020;36(12):820-825. 13. Wang L, Koch DD. Comparison of accuracy of a toric calculator with predicted vs measured posterior corneal astigmatism. J Cataract Refract Surg. 2023;49(1):29-33. 14. Stewart S, Yeo TK, Moutari S, McNeely R, Moore JE. Accuracy of Toric Intraocular Lens Formulas With Measured Posterior Corneal Astigmatism of Different Orientations. Am J Ophthalmol. Published online May 4, 2024. 15. Heath MT, Mulpuri L, Kimiagarov E, et al. Intraocular Lens Power Calculations in Keratoconus Eyes Comparing Keratometry, Total Keratometry, and Newer Formulae. Am J Ophthalmol. 2023;253:206-214. Media placement sponsored by Carl Zeiss Meditec AG
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