Review of intraocular lens power calculation formulas in eyes after corneal refractive surgery

The correct post-operative refractive outcome is a crucial aspect of phacoemulsification. Mostly, it relies of effective lens position (ELP) estimation resulting from the selection of appropriate intraocular lens (IOL) power calculation formula. ELP estimation is especially difficult in eyes that have undergone corneal refractive surgery (CRS) since quandaries in achieving an accurate corneal power. It is caused by incorrect measurement of anterior corneal curvature, changes in posterior corneal curvature and aberration of corneal refractive index (1.375). At least several dozen IOL power calculation formulas in eyes with previous CRS have been developed to date. Seventeen the most used formulas were described, and their accuracy was evaluated in this study. The trueness of the formulas was assessed using the mean absolute error (MAE), median absolute error and percentage of eyes with prediction error within ± 0.5 D and ± 1.0 D. In the most studies, Barrett True-K obtained the smallest MAE in previously hyperopic eyes. In previously myopic eyes, Barrett True-K yielded accurate results also, but the Okulix and the Triple-S formulas performed equally well. Thus, Barrett True-K usually achieves the accurate outcomes in IOL power calculation in eyes that have undergone CRS. However, there is still no consensus on the formula choice in post-refractive eyes.