No matter which IOL is used, the surgeon will need to select the appropriate power of IOL (much like an eyeglass prescription) to provide the patient with the desired refractive outcome. Traditionally, doctors use preoperative measurements including corneal curvature, axial length, and white to white measurements to estimate the required power of the IOL. These traditional methods include several formulas including Hagis, Hoffer Q, Holladay 1, Holladay 2, and SRK/T to name a few.[13] Refractive results using traditional power calculation formulas leave patients within 0.5D of target (Correlates to 20/25 when targeted for distance) or better in 55% of cases and within 1D (Correlates to 20/40 when targeted for distance) or better in 85% of cases.