The Impact Of Using Optional Variables On The Performance Of The Kane And Barrett Universal Ii Formulae

The Kane and Barrett Universal II (BUII) formulae are both recent IOL power calculation formulae that provide a set of entitled optional variables i.e., lens thickness (LT) and central corneal thickness (CCT) for the Kane formula and the white-to-white (WTW) distance, and LT for the BUII formula. Their effect on the prediction of the postoperative refractive error and their relative impact across subgroups of axial length (AL) is not clearly established. The aim of this study was to evaluate the effect of the use of optional variables for both these formulae in the postoperative prediction error and whether these contribute to an improvement of outcomes, across subgroups of axial length.

Centro Hospitalar e Universitário de Coimbra (CHUC), a tertiary public academic hospital in Coimbra, Portugal.

Retrospective case series of eyes submitted to uncomplicated cataract surgery. All patients underwent swept-source optical biometry (IOL Master 700®, Carl Zeiss) and the postoperative spherical equivalent (SE) was obtained through subjective refraction at the 6th postoperative week. Prediction error (PE) i.e., the difference between postoperative and formula-predicted SE was calculated for each formula. Mean (ME) and median (MedE) PE, mean absolute (MAE) and median absolute (MedAE) PEs, and the proportion of eyes within ±0.25, ±0.50, ±0.75, and ±1.00 diopters (D) of the PE were calculated. Calculations were performed with and without optional variables. Eyes were divided between short (AL<22 mm), medium (≥22 and <25 mm), and long (≥25mm).

We included 143 eyes with mean AL of 23.58±2.58mm. In short eyes (n=64), the Kane and BUII formulae had a MAE of 0.44/0.43, and a MedAE of 0.28/0.30. With optional variables, MAE was 0.43/0.44 and MedAE was 0.29/0.34, respectively. In medium eyes (n=39), both had MAE of 0.46 and MedAE of 0.34. With optional variables, MAE was 0.44/0.46 and MedAE was 0.36/0.33, respectively. In long (n=40) eyes the Kane and BUII formulae had a MAE of 0.38/0.36, and a MedAE of 0.37/0.35. With optional variables, MAE was 0.35/0.34 and MedAE was 0.32/0.36. The use of optional variables contributed mostly to a <0.1D change in PE without further improving prediction. Their use did not result in a significant change in the number of eyes within ±0.25-1.00D of PE.

The use of optional variables for the Kane and Barrett UII formulae did not seem to contribute to an improvement in postoperative refractive error prediction, this effect being sustained across the spectrum of axial lengths.