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Materials and Methods
We retrospectively reviewed the pre-operative data and the three-month post-
operative results of 200 myopic patients that have undergone Lasik surgery in one
clinical practice. At every visit, a complete eye examination was performed including a
manifest refraction. The Sim-K values obtained from the Atlas videokeratograph, version
A10.1 (Humphrey Systems) were used for pre- and post-Lasik corneal power
measurements. The Nidek EC-5000 (Nidek Co. Ltd, Japan) was used for all Lasik
surgeries.
For the purpose of this study, we randomly selected one operated eye from each
patient by using an eye selection randomization list. Table 1 shows the information
obtained from each selected eye: the pre-Lasik (Rs.pre) and the post-Lasik (Rs.post)
spectacle correction, the pre-Lasik (Kpre) and the post-Lasik K readings (Kpost).
Spherical equivalent values and average K values were used in presence of astigmatism.
In each case, the pre-Lasik (Rc.pre) and post-Lasik (Rc.post) refractive errors were
calculated at the corneal plane using the formula
Rc = Rs ./. (1-0.12Rs)
This formula assumes a vertex distance of 12mm. The amount of myopia corrected at the
corneal plane (CRc) was also measured for each case where
CRc= Rc.post Rc.pre
The cases were divided into two groups of 100 eyes each. Group I was used to
derive the equations needed to calculate Kc.rd and Kc.cd.
