Simulated Keratometry Versus Total Keratometry: Separate Evaluations in 932 Eyes with Prior Myopic LASIK and 372 Eyes with Prior Radial Keratotomy

Objectives: To evaluate simulated keratometry (SimK) and total keratometry (TK) in eyes with prior myopic LASIK and radial keratotomy (RK), separately. Methods: Patients scheduled for cataract surgery with prior myopic LASIK or RK were included for separate analysis. Ocular biometry was performed using IOLMaster 700 (Carl Zeiss Meditec AG, Jena, Germany). Descriptive statistics for SimK and TK, their difference, correlation, and agreement were evaluated. The factors influencing the difference between SimK and TK were investigated. Results: In total, 932 eyes with prior myopic LASIK and 372 eyes with prior RK were analyzed. Compared to TK, SimK was significantly higher by +0.61 D (95% CI, +0.60 to +0.63 D) in eyes with prior myopic LASIK but significantly lower by −0.13 D (95% CI, −0.15 to −0.11 D) in those with prior RK (both p < 0.001). SimK and TK were strongly correlated in both groups (r = 0.996 and 0.997, respectively; both p < 0.001). The 95% limits of agreement (LoA) were +0.10 to +1.12 D in eyes with prior myopic LASIK and −0.58 to +0.32 D in those with prior RK. The difference between SimK and TK was significantly associated with axial length (AL) and central corneal thickness (CCT) in both groups. Conclusions: In eyes with prior myopic LASIK, SimK was higher than TK, while the opposite was observed with prior RK. SimK and TK showed limited agreement in both groups and should not be assumed interchangeable, particularly in eyes after LASIK with longer AL or thinner CCT and eyes after RK with shorter AL or thinner CCT.