IOL Power Calculation After Laser-Based Refractive Surgery: Measured vs. Predicted Posterior Corneal Astigmatism Using the Barrett True-K Formula

: Background/Objectives: This study assessed the reliability of the Barrett True-K formula in patients who had undergone laser-based corneal refractive surgery by comparing outcomes using measured vs. predicted posterior corneal astigmatism (PCA) within the Barrett True-K No History formula. Methods: We selected 49 eyes out of 41 patients with a history of uncomplicated laser visual correction (LVC) that underwent cataract surgery between 2020 and 2024. The Front K1 and K2, the Back K1 and K2, the anterior chamber depth, the lens thickness, the horizontal white-to-white, and the central corneal thickness were measured using Pentacam. The axial length was measured using the IOL Master 500 or NIDEK AL-Scan. These data were then imported into the freely available online Barrett True-K calculator for post-LVC eyes, and the postoperative results were compared with the predicted IOL target. The cumulative distribution of the refractive prediction error, absolute refractive prediction error, and refractive prediction error were calculated as the difference between the postoperative spherical equivalent and the expected spherical equivalent for both the predicted and measured PCA calculations. Results: The results suggest improved accuracy with the Barrett True-K formula when incorporating measured PCA values, supporting the use of corneal tomography for optimized refractive outcomes in post-LVC cataract patients. Conclusions: It is always advisable to measure the posterior corneal surface using corneal tomography in all patients who have undergone LVC to achieve better refractive outcomes after cataract surgery.