Modified Kane formula trumps other IOL power formulas for keratoconus

The most accurate intraocular lens (IOL) power formula for patients with keratoconus is the modified Kane formula, while the SRK/T outdoes other traditional IOL power formulas, according to the results of a recent study.

In addition, all normal IOL formulas have resulted in hyperopic refractive outcomes that worsened as the corneal power increased.

This retrospective consecutive case series analysed data from 14 eyes of 147 patients with keratoconus who had preoperative IOLMaster biometry. A single eye for each eligible patient was randomly selected.

The authors then calculated the predicted refraction for each of the formulas (modified IOL power formulas: Holladay 2 with keratoconus adjustment and Kane keratoconus formula; traditional IOL power formulas: Barrett Universal 2, Haigis, Hoffer Q, Holladay 1, Holladay 2, Kane, and SRK/T) and compared these with the actual refractive outcome to show the prediction error.

Finally, a subgroup analysis was carried out based on the steepest corneal power measured by biometry (stage 1: ≤48 dioptres [D], stage 2: >48 D and ≤53 D, and stage 3: >53 D).

The following formulas were ranked based on the mean absolute prediction error (MAE): Kane keratoconus formula (0.81 D), SRK/T (1.00 D), Barrett Universal 2 (1.03 D), unmodified Kane (1.05 D), Holladay 1 (1.18 D), unmodified Holladay 2 (1.19 D), Haigis (1.22 D), Hoffer Q (1.30 D), and Holladay 2 with keratoconus adjustment (1.32 D).

The Kane keratoconus formula demonstrated a statistically significant lower MAE compared with all formulas, modified or otherwise (p<0.01). Furthermore, all nonmodified formulas had a hyperopic mean prediction error ranging from 1.72 to 3.02 D in stage 3 keratoconus.