Comparison of Predictability Using Barrett Universal II and SRK/T Formulas According to Keratometry

Purpose: To compare the predictability of intraocular lens (IOL) power calculation using the Barrett Universal II and the SRK/T formulas, according to the keratometry.

Methods: We retrospectively reviewed the clinical charts of 335 consecutive eyes undergoing standard cataract surgery. IOL power calculations were performed using the Barrett Universal II and the SRK/T formulas. We compared the prediction error, the absolute error, and the percentages within ±0.25, ±0.5, and ±1.0 D of the targeted refraction, 1 month postoperatively, and also investigated the relationship of these outcomes with the keratometric readings, using the two formulas.

Results: The prediction error using the SRK/T formula was significantly more myopic than that using the Barrett Universal II formula (the paired -test, < 0.001). The absolute error using the SRK/T formula was significantly larger than that using the Barrett Universal II formula (=0.006). We found a significant correlation between the prediction error and the keratometric readings using the SRK/T formula (Pearson correlation coefficient,  = -0.522, < 0.001), but there was no significant correlation between them using the Barrett Universal II formula ( = -0.031, =0.576).

Conclusions: The Barrett Universal II formula provides a better predictability of IOL power calculation and is less susceptible to the effect of the corneal shape, than the SRK/T formula. The Barrett Universal formula, instead of the SRK/T formula, may be clinically helpful for improving the refractive accuracy, especially in eyes with steep or flat corneas.