Comparison of Barrett and Kane keratoconic formulae in eyes with only posterior corneal changes

Abstract PURPOSE: The aim of this study was to compare the efficacy of Barrett Universal II (UII), Barrett total K, Barrett True-K keratoconus (KC), Kane, and Kane KC formulae in eyes with only posterior corneal changes. METHODS: A retrospective case series of eyes with normal anterior keratometry with only posterior corneal changes, aged between 45 and 75 years, and had undergone cataract surgery was analyzed. Subjects with any systemic illness, previous corneal surgery, corneal opacity, previous history of corneal inflammation, and subjects with missing data were excluded. For all patients, intraocular lens (IOL) power calculations were done using Barrett UII, Barrett total K, Barrett True-K KC predicted, Barrett True-K KC measured, Kane, and Kane KC formulae. For all patients, mean absolute error, median absolute error (MedAE), and percentage of eyes with absolute error spherical equivalent within 0.25D, 0.5D, and >0.51D were noted. RESULTS: Twenty-one eyes of 13 patients with a mean ± standard deviation age of 61.92 ± 7.08 years had undergone cataract surgery. The MedAE was least with predicted Barrett True-K KC (0.26), whereas it was highest with Barrett total K (0.31). However, the Kruskal–Wallis test did not reveal any statistical significant difference in absolute error among the various formulae. Predicted Barrett KC, Kane, and Kane KC each resulted in the highest percentage of eyes (47.62%) within ±0.25 diopters error. Overall, Barrett UII, measured Barrett KC, Kane, and Kane KC had the highest percentage of eyes (76.19%) within ± 0.50 diopters error. CONCLUSION: This study has reported the efficacy of various IOL power calculations’ formulae in unique cases where anterior corneas were normal and had the abnormal posterior cornea resulting in anterior–posterior asymmetry. Although clinically predicted Barrett True-K KC resulted in the least absolute error, statistically, it did not show any edge over other formulae including Kane KC in eyes with only posterior corneal changes.