Comparison of Predictability Using Barrett Universal II and SRK/T Formulas according to Keratometry
Kei Iijima, Kazutaka Kamiya, Yoshihiko Iida, Nobuyuki Shoji
Abstract
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 t -test, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mi>p</mml:mi><mml:mo><</mml:mo><mml:mn>0.001</mml:mn></mml:math>). The absolute error using the SRK/T formula was significantly larger than that using the Barrett Universal II formula (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:mi>p</mml:mi><mml:mo>=</mml:mo><mml:mn>0.006</mml:mn></mml:math>). We found a significant correlation between the prediction error and the keratometric readings using the SRK/T formula (Pearson correlation coefficient, r = −0.522, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M3"><mml:mi>p</mml:mi><mml:mo><</mml:mo><mml:mn>0.001</mml:mn></mml:math>), but there was no significant correlation between them using the Barrett Universal II formula ( r = −0.031, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M4"><mml:mi>p</mml:mi><mml:mo>=</mml:mo><mml:mn>0.576</mml:mn></mml:math>). 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.