The accuracy of intraocular lens (IOL) power calculation is important for the visual outcome of patients undergoing cataract extraction and IOL implantation. But if those patients undergoing cataract extraction and IOL implantation have a previous refractive surgery the accuracy of IOL power calculation then will be lost. Sources of errors of IOL calculation after corneal refractive surgeries : 1-Instrument error as standard keratometery and corneal topography cannot accurately measure the corneal power, 2-Index of refraction error because the relationship between the anterior and posterior corneal curvatures is changed in PRK, LASIK, and LASEK, but not in RK and 3-Formula error as most third- or fourth-generation IOL formulas Hoffer Q, Holladay 1 and 2 and SRK/T, (but not the Haigis formula) use the flatter corneal power (K) than normal K in RK, PRK, LASIK, and LASEK eyes causes an error in prediction of effective lens position (ELP) because the anterior chamber dimensions do not really change in these eyes.