Henry B. Wallace, Stuti L. Misra, Sunny Sixiao Li, Charles N.J. McGhee, James McKelvie
Purpose: To determine the accuracy of intraocular lens (IOL) power prediction using three formulae, Hill-RBF(RBF), Barrett Universal II(BU), and SRK/T. Methods: One-hundred and thirteen eyes of 94 pro- spectively enrolled patients listed for cataract sur- gery were recruited once formal ethics approval was obtained. All the patients underwent preoperative IOLMaster-500 biometry. Optimal IOL power and predicted refractive outcomes were calculated by entering these data into the IOL power calculation formulae. Predicted refraction was compared with actual refractive outcomes measured at 1-week and 1-month follow-up. Statistical analysis was com- pleted using R software.
Results: Mean axial length was 23.4 1.0mm (min=21.1, max=27.9). Mean keratometry was
44.0 1.6 Dioptres(D) (min=38.8D, max=48.7D). The mean absolute prediction errors (APE) at 1-month were: RBF; 0.49 0.38D, BU; 0.50 0.40D, and SRK/T; 0.48 0.35D. There were no signiftcant dif- ferences in APE between any of the formulae at 1- week (X2(2)=2.22, p-value=0.33) and 1-month (X2
(2) =1.00, p-value=0.61). The BU formula had the highest proportion of eyes within 0.25D(34%) and 0.5D(62%) of predicted at 1-month. The SRK/T formula had the highest proportion of eyes within 1D(91%) of predicted at 1-month. For SRK/T data, second-order polynomial regression resulted in a signiftcantly better ftt than reduced models (F=9.8439, p-value=0.002).
Conclusions: There are no signiftcant differences between the three formulae and they can be used interchangeably for medium length eyes (22- 24.5mm). SRK/T is less accurate at IOL power pre- diction for eyes outside the medium range of axial length. IOL power prediction was equally accurate for eyes outside of the medium range using the BU and RBF formulae.