Effect of the ratio of axial length to keratometry on SRK/T intraocular lens power calculations for eyes with long axial lengths

This retrospective study explored the effect of the ratio of axial length (AL) to average keratometry (K) on intraocular lens power calculation in long eyes. The clinical records of eyes that had an AL of 26.0 mm or longer, and underwent cataract surgery with intraocular lens implantations, were reviewed. This study was approved by the institutional review board of Miyata Eye Hospital. Preoperative biometry data were obtained using optical low-coherence reflectometry. Prediction errors in the use of the SRK/T formulas were obtained from manifest refraction spherical equivalents one month postoperatively. Significant factors inducing prediction errors were examined using stepwise multiple regression analysis with descriptive factors of AL, K value, and their ratio (AL/K). Clinical records related to 49 long eyes of 49 patients, and 93 eyes of 93 patients with normal AL, were evaluated. Stepwise multiple regression analysis revealed that the AL/K was a significant factor increasing the prediction errors (P = 0.0003). With the regression equation, 98% of prediction errors with the use of the SRK/T formula were within ±1.00 D of differences. For our sample of 49 long eyes, the ratio of AL to K was a significant factor inducing hyperopic prediction errors with the use of SRK/T for long eyes.