Accuracy of keratoconus specific formulae compared to standard formulae for IOL power calculation in patients with keratoconus

Author Block: Nicolas Kahuam , Jennifer YM Ling, Alfonso Iovieno, Sonia N. Yeung.  University of British Columbia.

Author Disclosure Block: N. Kahuam:  None.  J. Ling:  None.  A. Iovieno:  None.  S. Yeung:  None., Nicolas Kahuam: Not Current  Jennifer YM Ling: Not Current  Alfonso Iovieno: Not Current  Sonia N. Yeung: Not Current

Abstract Title: Accuracy of keratoconus specific formulae compared to standard formulae for intraocular Lens Power calculation in patients with Keratoconus

Abstract Body: Purpose:  To compare the accuracy of Keratoconus-specific formulae for toric and non-toric intraocular lenses in eyes with keratoconus undergoing cataract surgery.  Study Design:  Retrospective chart review  Methods:  A retrospective chart review was conducted on cataract surgeries performed at the Cornea Service in the Department of Ophthalmology and Visual Sciences of the University of British Columbia from 2000 to 2020. Inclusion criteria were patients with keratoconus diagnosed by a corneal subspecialist based on clinical examination and corneal topographical findings. Exclusion criteria included previous corneal surgery and intraoperative or postoperative complications. The SRK II, SRKT, Hoffer Q, Holladay, original Kane, Kane keratoconus, Barrett Universal 2, Barrett true K, Hill RBF, Hoffer QST, and Pearl DGS formula were calculated. The postoperative mean absolute prediction error was calculated for each formula, the Kolmogorov-Smirnov test was used to assess the normality of the data and an analysis of variance was used to analyze differences between groups and subgroups.  Results:  A total of 130 eyes were included in the study. Of these, 108 eyes received non-toric IOLs, while 24 eyes toric IOLs. The mean keratometry (K) values were K1 45.18 (SE 0.30, 95% CI 44.58, 44.78) and K2 47.51 (SE 0.32, 95% CI 46.86, 48.16) and K average 46.34 (SE 0.30, 95% CI 45.74, 46.94). There were no statistically significant differences in mean absolute error and mean predicted error among the formulae used for calculating IOL power. The mean absolute error for each formula was Kane KC 0.89 (SE 0.07, 95% CI 0.73, 1.04), Kane 0.89 (SE 0.07, 95% CI 0.74, 1.04), Barrett true K 0.87 (SE 0.07, 95% CI 0.72, 1.04), Barrett 0.88 (SE 0.07, 95% CI 0.70, 1.00), SRK II 0.85 (SE 0.07, 95% CI 0.70, 1.00), SRK/T 0.84 (SE 0.07, 95% CI 0.69, 0.99), Hoffer Q 0.84 (SE 0.07, 95% CI 0.69 , 0.99), Holladay I 0.85 (SE 0.7, 95% CI 0.07, 1.00), EVO 0.81 (SE 0.07, CI 0.74, 1.05), Hill RBF 0.86 (SE 0.07, 95% CI 0.70. 1.01), Hoffer QST 0.88 (SE 0.07, CI 95% 0.73, 1.03), Pearl DGS 0.89 (SE 0.07, CE 0.74, 1.03).  Conclusions:  We did not observe a statistically significant difference in predicted error and absolute error in Keratoconus-specific formulae when compared to conventional formulae for IOL power calculation for cataract surgery in keratoconus patients.