4
Laser in situ keratomileusis (Lasik) is gaining in popularity as the method
of choice for the correction of near-sightedness in young adults. More patients in their
40s and 50s are now undergoing refractive corneal surgery in their quest to achieve
emmetropia. A number of these patients will develop cataracts, and they will probably
expect excellent uncorrected post-operative visual acuity, just like after their refractive
surgery. However, early experience with eyes that had undergone refractive surgery has
shown that the refractive predictability after cataract surgery is relatively poor (1-4).
With standard IOL power calculations using the post-Lasik K readings (Kpost), the
power of the implant used during cataract surgery is usually underestimated resulting in a
post-operative hypermetropic surprise. Different investigators have shown that after
refractive surgery, the true value of the corneal power is actually lower than the K
readings measured by keratometry or by videokeratography (1-5). The most accurate way
to obtain the correct keratometric values is the history-derived method (Kc.hd) where the
myopic correction achieved at the corneal plane is algebraically added to the pre-
refractive corneal power (6-12). However, this method requires knowledge of the pre-
refractive corneal power and the amount of myopic correction obtained with the
refractive surgery.
The purpose of this study is two-fold. First, we are describing two different
methods that can be used to calculate the correct post-Lasik K values when the history-
derived method can not be used. These methods were derived from the review of 100
consecutive Lasik cases. A corrected keratometric value (Kc.rd) can be obtained by using
