NEWS & OPINION 46 EWAP MARCH 2023 by setting the actual postop refraction to the target refraction in the Barrett True-K and ASCRS calculators. Those calculators were used to calculate the predicted IOL power, and the difference between the predicted IOL power and the actual implanted IOL power was the IOL prediction error. The IOL prediction error was multiplied by 0.7 to estimate the refractive error at the spectacle plane since the ASCRS calculator does not provide an expected refraction for a given lens recommendation. Results In the post-myopic ablation group of 96 eyes of 81 patients, the mean IOL prediction errors were analyzed by a one-sample t-test for each formula to assess whether the error was statistically different from 0 (plano). The Barrett True-K, ASCRS calculator average, and Haigis-L did not have an IOL prediction error statistically different from 0, while the other calculators did. In the post-hyperopic group of 47 eyes from 34 patients, similarly, the Barrett True-K and ASCRS calculator average were not statistically different from 0. The mean refractive prediction error as well as the mean and median absolute refractive prediction errors were also analyzed. There was a statistically significant difference in the variances between the absolute refractive errors of all calculators, and post-hoc paired t-tests showed that the Barrett True-K also had the lowest standard deviation and residual absolute refractive error compared to all other formulas for both myopic and hyperopic ablations. In addition, the Barrett True-K achieved the highest proportion of eyes with postop refraction within 0.25 D (44.8%) and within 0.50 D (71.9%), though this difference was not statistically different from the ASCRS mean proportion (38.3% for within 0.25 D and 65.6% within 0.50 D). Outlier analysis was also performed for eyes with greater than 1.00 D of IOL prediction error. In 12 post-myopic eyes and 6 post-hyperopic eyes where the IOL prediction error of the Barrett True-K was greater than 1.00 D, no other formula outperformed the Barrett True-K, and no outliers were detected in the biometry measurements. Discussion This study demonstrated the advantages of the Barrett True-K formula in eyes for both post-myopic and post-hyperopic ablation. The authors demonstrated how the Barrett True-K formula produced the highest proportion of eyes IOL power calculations after LASIK or PRK: Barrett True-K biometer-only calculation strategy yields equivalent outcomes as a multiple formula approach Ferguson TJ, et al. J Cataract Refract Surg. 2022;48:784–789 Purpose: To compare the accuracy of intraocular lens (IOL) power calculations performed using the biometer-embedded Barrett True-K formula versus a multiple formula approach using the ASCRS post-refractive calculator in eyes with prior myopic or hyperopic refractive surgery. Setting: Cleveland Clinic Cole Eye Institute, Cleveland, Ohio Design: Retrospective, consecutive case series Methods: Patients who underwent cataract surgery with a history of corneal refractive surgery were included. For each formula, the IOL prediction error (PE) and refractive PE was calculated. Main outcome measures included mean absolute error (MAE) as well as the percentage of eyes within ±0.25, ±0.50 and ±1.00 diopters (D). Results: A total of 96 post-myopic eyes and 47 post-hyperopic eyes were analyzed. In the post-myopic cohort, the Barrett True-K had the lowest MAE (0.36 D) followed by the Haigis-L (0.41 D). The Barrett-True K had a significantly higher percentage (44.8%) of eyes within ±0.25 D in comparison to the Haigis-L (34.4%), which had the second highest percentage (P<.01). In the post-hyperopic cohort, the Barrett True-K had the lowest MAE (0.41 D) followed by the ASCRS–mean (0.46). The Barrett True-K and ASCRS–mean had the highest percentage of eyes within ±0.25 D (42.6% vs 38.3%, P=.16). Conclusion: The Barrett-True K formula built into the biometer performed equivalently to a multiple formula approach on the ASCRS online calculator in both post-myopic and post-hyperopic eyes. This approach reduces the potential for transcription error from data entry for lens power calculation approaches that require manual data entry. within 0.25 D and 0.50 D of the target refraction, lowest mean and absolute refractive error, and lowest standard deviation of those errors. In addition, for 12 post-myopic and 6 post- hyperopic outliers, the Barrett True-K still outperformed all other formulas. This finding is significant because the Barrett True-K formula is embedded into the IOLMaster and Lenstar, improving convenience and eliminating the possibility for transcription error when transferring data into the online ASCRS calculator. The accuracy of the Barrett True-K formula for a refractive outcome within 0.50 D of the target is approaching the accuracy reported in the literature for eyes even without a history of refractive surgery. It should be noted that the cataract surgeries included in continued on page 50
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