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; 11:490-493