Correlating Kane formula with existing intraocular lens formulae for corneal curvatures and axial lengths

To evaluate the predictability of the Kane formula in estimating postoperative refractive outcome with various corneal curvatures and axial lengths (ALs) besides comparing with existing intraocular lens (IOL) formulae.

A prospective cross-sectional study was carried out among patients having uneventful cataract surgery at an eye hospital. A total of 50 eyes were considered for the study. The corresponding A-constant for the model of IOL implanted into the patient's eye was taken along with the actual power of IOL implanted and corresponding predicted power for the IOL power inserted were taken for all the chosen formulae and was termed as "Adjusted Predicted Refractive Power." This was compared with the actual refractive outcome and the absolute error (AE) was measured. The eyes were separated into groups in terms of corneal curvature as flat (<42D), medium (42D-46D), and steep (>46D) corneas. In terms of AL, it was grouped as short (≤22 mm), medium (>22.0-<24.0 mm), and long (>24.0 mm) eyes.

The study included 50 eyes and the mean AE for all the selected formulae were calculated for each group. Over the entire corneal curvature range, none of the formulae showed any significance when compared with the Kane formula (P > 0.05). In short AL, SRK-T formula had a statistical significance over the Kane formula (P = 0.043), whereas no other group had any significance over the Kane formula in AL groups.

The study shows, all formulae (SRK-T, Holladay1, Hoffer Q, Hill RBF, Barrett Universal II, Kane) are interchangeable to predict the IOL power for any of the corneal curvature and ALs.