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IOL Power Calculations 
Clinical History Method.^{1,2}The Clinical History Method for corneal power estimation was first described by Holladay and later by Hoffer as:
Central corneal power by keratometry will be referred to in diopters (D), even though it is better termed keratometric diopters. This is due to the fact that the cornea has a different index of refraction than keratometers, or corneal topographers (1.3333 vs. 1.3375)^{7} Corrected for an estimated vertex distance of 12 mm, the historical estimation of the central corneal power of the right eye following LASIK would be carried out as follows:
Corrected for an estimated vertex distance of 12 mm, the historical estimation of the central corneal power of the left eye following LASIK would be carried out as follows:
If you are unfamiliar with how to correct for vertex distance, follow this link to an Excel spreadsheet for Correcting for Vertex Distance. Be sure to maintain the correct sign (+ or ) when entering the refractive data, or the results will not be accurate. References 1. Holladay JT. Consultations in refractive surgery. Refract Corneal Surg 1989; 5:203 2. Hoffer KJ. Intraocular lens power calculation for eyes after refractive keratotomy. J Refract Surg 1995; 11:490493
