Comparison of three newer generation freely available intraocular lens power calculation formulae across all axial lengths.

Purpose: The aim of this study is to evaluate the accuracy of three newer generation formulae (Barrett Universal II, EVO, Hill-RBF 2.0) for calculation of power of two standard IOLs-the Acrysof IQ and Tecnis ZCB00 across all axial lengths. Methods: In this retrospective series, 206 eyes of 206 patients, operated for cataract surgery with above two IOLs over the last 6 months, were included in the study. Preoperative biometry measurements were obtained from LenstarLS900. By using recommended lens constants, the mean error for each formula was calculated and compared. Then, the optimized IOL constants were calculated to reduce the mean error to zero. Mean and median absolute errors were calculated for all eyes and separately for short (AL<22.5 mm), medium (22.5-24.5 mm), and long eyes (>24.5 mm). Absolute errors and percentages of eyes within prediction errors of ±0.25 D, ±0.50 D, ±0.75 D, and ±1.00 D were compared. Results: Prediction error with using recommended lens constants was significantly lower in the Barrett Universal II formula as compared to the other two formulae. However, after optimizing lens constants, there were no significant differences in the absolute errors between the three formulae. The formulae ranked by mean absolute error were as follows: Barrett Universal II (0.304 D), EVO (0.317 D), and Hill-RBF (0.322) D. There were no significant differences between absolute errors in the three formulae in each of the short-, medium-, and long-eye subgroups. Conclusion: With proper lens constant optimization, the Barrett Universal II, EVO, and Hill-RBF 2.0 formulae were equally accurate in predicting IOL power across the entire range of axial lengths.

Verion digital marking versus smartphone-assisted manual marking and isolated manual marking in toric intraocular lens implantation.

Purpose: To compare the accuracy of isolated manual marking and smartphone-assisted manual marking with the Verion image-guided system for toric intraocular lens (IOL) implantation. Methods: In this prospective observational study, 42 eyes of 36 patients planned for phacoemulsification with toric IOL implantation with corneal astigmatism >1D as measured on Lenstar LS 900 optical biometer were included. Patients were preoperatively registered and photographed on the Verion image-guided system. In the operating room, the patient's eye was manually marked at the 6 o' clock limbus (Manual axis-90°) on slit-lamp in sitting position. Next, using the smartphone android app-iToric Patwardhan, the exact mark axis was confirmed (Smartphone axis). Following this, the patient was taken on the operation table where the mark axis was confirmed with Verion digital overlay on an external screen (Verion axis). The absolute angular deviation of manual axis from Verion was compared with the absolute angular deviation of the smartphone axis from Verion as the primary outcome measure. Results: The mean absolute angular deviation between the smartphone axis and the Verion axis was 2.62°, which was significantly lower (P < 0.05) than that between the manual axis and Verion axis (4.60°). Moreover, the intraclass correlation coefficient between the smartphone axis and Verion axis was 0.88 indicating a strong agreement between the two. Conclusion: Smartphone-assisted manual marking significantly improves the accuracy of manual marking alone when comparing with the Verion Digital Marker system for toric IOL implantation.