Intraocular lens power calculation in the elderly population using the Kane formula in comparison with existing methods

Abstract

Purpose: To assess the accuracy of the Kane formula for intraocualr lens (IOL) power calculation in comparison with established formulas in the elderly population.

Setting: Shiley Eye Institute, University of California San Diego, USA.

Design: Retrospective cohort.

Methods: Retrospective data from 90 patients (90 eyes) aged 75 years or older who underwent uneventful cataract surgery with SN60WF intraocular lens (IOL) implantation were evaluated. The first operated eyes of patients with final corrected distance visual acuity 20/40 or better and axial length 22 to 26 mm were included. Prediction errors were calculated for Barrett Universal (BU) II, Haigis, Hoffer Q, Holladay 1, Kane, and SRK/T formulas. A subgroup analysis based on age (75-84 and ≥85 years old) was performed.

Results: Use of both BUII and Kane formulas resulted in the highest percentage of eyes with prediction errors within ±0.50 diopters (D) (72% each) and significantly higher than Hoffer Q, Holladay 1, and SRK/T (P = .001). Rates of predictability within ±0.25 D and ±1.00 D were 31% to 38% and 87% to 92%, respectively, with no significant differences between formulas. No statistically significant difference was seen between formulas in the median absolute error. These tendencies remained consistent in both age groups when analyzed separately. Subgroup analysis showed better predictability of all formulas in the younger age group.

Conclusions: To the authors' knowledge, this is the first study evaluating the Kane formula exclusively in the elderly population. The Kane formula was found to be of equal accuracy to the BUII and superior to the Hoffer Q, Holladay 1, and SRK/T formulas. Very elderly patients might have reduced refractive precision using all formulas.

Fig. 1:

Stacked histograms comparing the percentage of cases within ±0.25 D, ±0.50 D and ±1.00 D of predicted spherical equivalent refraction outcome for the entire data set. BUII = Barrett Universal II. * Kane and BUII > Hoffer Q, Holladay 1 and SRK/T (p<0.05).