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We are herein describing a new clinically-derived method based on a regression
equation between Kc.hd and Kpost. The drawback of this formula is that the correction
does not relate to the amount of treatment obtained by Lasik; in other words, a -10 D and
a -1 D treatment with the same measured post-operative K readings would have the same
adjustment. Several studies (9-12) have clearly shown that the amount of error is directly
related to the amount of treatment. However, this study attempts to derive a mathematical
formula to adjust the K readings after Lasik and to more accurately determine IOL power
in these patients when neither the pre-Lasik K readings nor the amount of myopia
corrected are known. Many patients will not know or be able to obtain pre-op data when
the cataract surgery is planned which could be many years after Lasik. The formula
utilizes only data available at the time of cataract surgery, mainly the post-Lasik K
readings. Further evaluation of this method in a prospective study will be needed to
establish its validity.
When it is entered into a standard IOL power formula, the post-Lasik K readings
are not only used as a measure of the corneal power but also to calculate the effective
lens position (ELP), which is the estimated post-operative distance between the anterior
corneal surface and of the principle plane of a thin IOL. This measurement is also
referred to as the pseudophakic anterior chamber depth (ACD). Modern IOL power
calculation formulas (18-22) utilize different methods to calculate ELP; however, they all
use the keratometric values in their calculations. In normal cases, a flatter corneal
measurement signifies a shallower ACD. The IOL power formulas will then calculate a
smaller ELP and a less powerful IOL to achieve emmetropia. After Lasik surgery, the
anterior corneal surface is flattened but the ELP is unaltered. The pre-Lasik K values
