Dispersion Between 5 New Generation Formulas As Prediction Factor Of Iol Power Calculation Accuracy

To evaluate the factors involved in the accuracy of intraocular lens power calculation and to assess the role of the variance between the results provided by 5 new generation formulas as a predictor of intraocular lens calculation accuracy.

General University Hospital of Elche (Alicante, Spain).

In this retrospective interventional case series, optical biometry measurements of the Lenstar LS 900 were automatically entered with the aid of a custom-made computer program into the following online calculators: Barrett Universal II (BUII), PEAL-DGS, RBF 3.0, EVO and Kane. The mean of the absolute errors of the formulas was set as dependent variable. A multivariable linear regression was performed with the software IBM-SPSS v. 21. The range between expected residual refraction calculated by the mentioned formulas, axial length (AL), mean keratometry (K), anterior chamber depth (ACD), white-to-white (WTW), lens thickness (LT), central corneal thickness (CCT) and IOL power were entered as independent variables.

292 eyes of 292 patients were evaluated. Mean age was 72.52±7.33 years; mean average keratometry was 44.06±1.55D; mean AL was 23.37±1.16 mm; mean ACD was 3.09±0.35 mm; mean WTW was 11.93±0.42 mm; mean LT was 4.57±0.36; mean CCT was 542.33±34.13 µm and mean IOL power was 22.05±3.24 D. The range between expected refractions was correlated with the average absolute error in the univariate analysis (rho of Spearman 0.206; p<0.001) and the number of formulas achieving +-0.5D accuracy (rho -0.234; p<0.001). In the multivariate analysis, this correlation was non-statistically significant (p = 0.154). With a range value between predictions >0.5D, the positive predictive value of getting 2 or less formulas in +-0.5D absolute error was 92%.

The dispersion between the expected results of the formulas is correlated with the accuracy of IOL power calculation. The variability between the predictions can serve as an estimate of how well our patient is represented in the databases with which the calculation formulas were created. Eyes with abnormal powers or biometric measurements are less common and therefore less precision of the calculation is expected. Consequently, variability between predictions was not a significant predictor in multivariate analysis. Values of range of predictions greater than 0.5D indicate great chances of having a postoperative refractive error out of the +-0.5D range.