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Original article
Comparison of the Kane formula with existing formulas for intraocular lens power selection
  1. Benjamin J Connell1,
  2. Jack X Kane2
  1. 1Eye Surgery Associates, Melbourne, Victoria, Australia
  2. 2Royal Victorian Eye and Ear Hospital, Melbourne, Victoria, Australia
  1. Correspondence to Dr Benjamin J Connell; benconnell{at}outlook.com.au

Abstract

Objective To compare the accuracy of a new intraocular lens (IOL) power formula (Kane formula) with existing formulas using IOLMaster, predominantly model 3, biometry (measures variables axial length, keratometry and anterior chamber depth) and optimised lens constants. To compare the accuracy of three new or updated IOL power formulas (Kane, Hill-RBF V.2.0 and Holladay 2 with new axial length adjustment) compared with existing formulas (Olsen, Barrett Universal 2, Haigis, Holladay 1, Hoffer Q, SRK/T).

Methods and analysis A single surgeon retrospective case review was performed from patients having uneventful cataract surgery with Acrysof IQ SN60WF IOL implantation over 11 years in a Melbourne private practice. Using optimised lens constants, the predicted refractive outcome for each formula was calculated for each patient. This was compared with the actual refractive outcome to give the prediction error. Eyes were separated into subgroups based on axial length as follows: short (≤22.0 mm), medium (>22.0 to <26.0 mm) and long (≥26.0 mm).

Results The study included 846 patients. Over the entire axial length range, the Kane formula had the lowest mean absolute prediction error (p<0.001, all formulas). The mean postoperative difference from intended outcome for the Kane formula was −0.14+0.27×1 (95% LCL −1.52+0.93×43; 95% UCL +0.54+1.03×149). The formula demonstrated the lowest absolute error in the medium axial length range (p<0.001). In the short and long axial length groups, no formula demonstrated a significantly lower absolute mean prediction error.

Conclusion Using three variables (AL, K, ACD), the Kane formula was a more accurate predictor of actual postoperative refraction than the other formulae under investigation. There were not enough eyes of short or long axial length to adequately power statistical comparisons within axial length subgroups.

  • cataract
  • lens

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

https://doi.org/10.1136/bmjophth-2018-000251

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    Footnotes

    • Contributors BC and JK planned the study, analysed the data, drafted, read and approved the manuscript. BC collected the data and submitted the study. BC and JK supervised the study and are its guarantors.

    • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

    • Competing interests JK is the owner of the JXK formula.

    • Patient consent for publication Not required.

    • Ethics approval Approval was obtained from the Royal Victorian Eye and Ear Hospital Human Research and Ethics Committee.

    • Provenance and peer review Not commissioned; externally peer reviewed.