Improving, the prediction accuracy of the SRK/T formula: The T2 formula

PURPOSE To investigate the causes of nonphysiologic behavior of the SRK/T formula, assess their clinical significance, and develop and evaluate solutions SETTING Two NHS ophthalmology departments, United Kingdom, and a private practice, United States DESIGN Evaluation of technology METHODS The individual steps of the SRK/T formula were examined for nonphysiologic behavior, and the clinical significance of behaviors was assessed with reference to a database of biometry and refractive outcomes in 11 189 eyes The full data set was divided into 2 subsets, the first to develop solutions to nonphysiologic behavior of the SRK/T formula and the second to evaluate their performance RESULTS ThE SRK/T formula showed nonphysiologic behavior in the calculation of corrected axial length and corneal height Although the former is of little clinical significance, the latter showed a systematic error that contributes to inaccurate intraocular lens (IOL) power prediction The T2 formula was developed using a regression formula for corneal height derived from the development subset Comparison of the performance of the T2 and SRK/T formulas using the evaluation subset showed significant improvement in the mean absolute error with the 12 formula (0 3064 diopter [D] versus 0 3229 D, P< 0001) On average, the prediction error with the T2 formula was 9 7% less than with the SRK/T formula, with significantly higher proportions of eyes within +/- 0 50 D of target (P< 0001) CONCLUSIONS The SRK/T formula has nonphysiologic behavior that contributes to IOL power prediction errors A modification to the formula algorithm, the T2 formula, can be directly substituted for SMUT, resulting in significantly improved prediction accuracy