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should be entered into the formula to calculate the precise ELP. An error in the ELP
measurement will occur if the post-Lasik K values are used instead of the pre-Lasik K
values. A 1mm error affects the final refraction by approximately 1.5 D. Furthermore, its
effect is cumulative to the error produced by the corneal power's overestimation, yielding
the high hyperopic surprises reported in the literature (1-4). A comparison of these
formulas shows that, after refractive surgery, the Hoffer-Q formula yields a higher IOL
power for emmetropia than the other formulas, thus decreasing the refractive error after
cataract surgery (11). However, the corneal power measurements still need to be
corrected by the history-derived method, the refraction-derived method or the clinically-
derived method to obtain the most accurate results.
In our study, we compared the new clinically-derived method and the refraction-
derived method to calculate the correct corneal power to the history-derived method,
using the latter as a benchmark. A-scan measurements of the axial length were not
performed in our cases. A better benchmark for comparison would be in determining the
IOL power prior to Lasik surgery utilizing standard calculation techniques with K
readings and axial length measurements. Further prospective studies are needed to
confirm our results and establish the validity of these methods used to correct the corneal
power measurements for IOL power calculations after Lasik.
