 The accuracy of IOL calculation is important for the visual outcome of patients undergoing cataract extraction and IOL implantation. Different formulas such as Holladay I, HofferQ, SRKT have been used with excellent results. All formulas use the corneal power among other factors to calculate the IOL power. Corneal refractive surgery i.e. radial keratotomy RK, photorefractive keratectomy PRK, and Laser in situ keratomileusis LASIK changes the corneal power; therefore, it is difficult to measure the true corneal power after surgery by any form of direct measurement, such as keratometry, or corneal topography. Keratometry and topography assume a normal relationship between the anterior and posterior corneal curvatures, and measure the anterior corneal radius. RK for myopia flattens both the anterior corneal radius and the posterior corneal radius while PRK and LASIK for myopia flattens the anterior corneal radius but leaves the posterior corneal radius mostly unchanged. 