Intraocular lens power calculation in virgin eyes: Accuracy of the Barrett Universal II formula and a Ray tracing software.

PURPOSE: To compare the accuracy of Sirius ray tracing software with the Barrett Universal II formula for intraocular lens power prediction in virgin eyes. METHODS: Retrospective case series including 86 eyes that have undergone uneventful cataract surgery with SN60WF implantation. The median absolute error, mean prediction error, variance, and the percentage of eyes within ± 0.25 D, ± 0.50 D, ± 0.75 D, and ± 1.00 D of the prediction error in refraction were calculated. The correlation of prediction error with different baseline parameters was investigated. RESULTS: No differences were found between the median absolute error of the Barrett Universal II formula (0.226 D) and the ray tracing software with different intraocular lens centerings; apex (0.331 D), limbus (0.345 D), and pupil (0.342 D) (p = 0.084). The variance, from lowest to highest, was the Barrett Universal II (0.144 D2), ray tracing-limbus (0.285 D2), ray tracing-pupil (0.285 D2), and ray tracing-apex (0.287 D2) (p = 0.027). The Barrett Universal II formula showed a higher percentage of eyes within ± 0.25 D (56.98%), ± 0.50 D (82.56%), and ± 0.75 D (93.02%) compared to ray tracing software (p < 0.01). A significant correlation between the prediction error of the Barrett Universal II formula and corneal diameter (r = 0.322, p = 0.002) and pupil diameter (r = 0.230, p = 0.033) was found. Also, a positive correlation between the prediction error of Sirius ray tracing and axial length (p < 0.001) and pupil diameter (p = 0.01) was found. CONCLUSION: There is a trend of the Barrett Universal II formula to be more accurate than Sirius ray tracing software for intraocular lens power calculation in virgin eyes. This should be confirmed in future prospective comparative studies.

Color LED reflection topography: validation of equivalent keratometry reading for IOL power calculation in eyes with previous corneal myopic refractive surgery.

PURPOSE: To compare the accuracy of the equivalent keratometry reading (EKR) from a color LED corneal topographer (Cassini) with that of other no-history formulas for intraocular lens (IOL) power calculation in eyes with previous myopic excimer laser surgery. SETTING: Centro de Oftalmología Barraquer, Barcelona, Spain. DESIGN: Retrospective case series. METHODS: The refractive outcomes of the Cassini EKR entered into the Haigis formula were compared with those of the Barrett True-K, Haigis-L, and Shammas-PL formulas and the Triple-S method combined with the Haigis formula. Optimized lens constants for virgin eyes were used. The mean prediction error (PE), the median absolute error (MedAE), and the percentage of eyes with a PE within ±0.25 diopter (D), ±0.50 D, ±0.75 D, and ±1.00 D were calculated. RESULTS: The study comprised 37 patients (37 eyes). The Haigis-L, Shammas-PL, and Barrett True-K no-history methods produced a myopic mean PE that was significantly different from zero (P < .001, P < .001 and P = .004, respectively), whereas the mean PEs of Cassini EKR and the Triple-S combined with the Haigis formula were not different from zero (P > .05). Repeated-measures analysis of variance disclosed a significant difference among the PE of all methods (P < .0001). The MedAE of the Cassini EKR, Barrett True-K, Haigis-L, Shammas-PL, and Triple-S was, respectively, 0.34 D, 0.34 D, 0.49 D, 0.48 D, and 0.31 D (P = .0026). CONCLUSIONS: The performance of the combination of standard Haigis formula with Cassini EKR was comparable to other no-history formulas in eyes with previous myopic excimer laser surgery.