Comparison Of Prediction Accuracy Between Total Keratometry And Conventional Keratometry In Cataract Surgery With Diffractive Multifocal Intraocular Lens Implantation.

To compare the prediction accuracy of the conventional keratometry(K) with total keratometry(TK) of a swept-source optical coherence tomography(SS-PCT) biometer(IOLMaster 700, Carl Zeiss Meditec) in eyes with a normal cornea that underwent cataract surgery implanting single diffractive multifocal intraocular lens(IOL) model(Alcon TFNT) using the older formulas(Hoffer Q, Holladay 1, SRK/T and Haigis)and newer formulas(Barrett Universal ll, EVO 2.0, Kane and PEARL-DGS formula). 

Miracle Eye Clinic, Seoul, Korea.

K, TK, posterior keratometry(PK), central corneal thickness(CCT), axial length(AL), anterior chamber depth(ACD), lens thickness(LT) and horizontal corneal diameter(white to white, WTW) were recorded. Refractive predictions were calculated by each formula with K and TK, respectively. The mean prediction error(ME), standard deviation(SD), median absolute error(MedAE), mean absolute error(MAE), and percentages within an absolute error of 0.25D(Diopter), 0.50D, 0.75D and 1.0D were calculated. The effective lens position(ELP) prediction algorithm of the Haigis formula was experimentally modified by excluding or including variables and optimized to investigate whether the number of variables may influence the difference between the K and TK. 

Records of a total of 3100 eyes of 3100 patients were retrospectively reviewed. The accuracies of TK were similar to K in the older formulas. In contrast, TK yielded significantly lower SD and absolute errors than K in the newer formulas. The experiments with the Haigis formula's ELP prediction algorithm demonstrated that while there was no difference in accuracy between the K and TK when the keratometric value was added with or without ACD(AL, ACD, keratometry or AL, keratometry), the TK significantly outperformed K when more variables(LT, WTW or both together) were also added, more or less reflecting the older and newer formulas' results.

For calculating the IOL power in eyes with the normal cornea, which occupies most cataract surgery patients, using the TK value might benefit the newer formulas which employ additional variables, such as LT and WTW, but not the older formulas. 
The influence of the keratometric value on the refractive prediction appears to increase when the formula uses more variables, therefore resulting significant difference between the K and TK data.