Poster Number: P90 Category: Intraocular Surgery (Cataract and Refractive) Optimization of IOL Power Calculation Constants: By Unit or by Surgeon? Nathaniel E Knox Cartwright, MA, MRCOphth Bristol Eye Hospital, Bristol, UK Financial Disclosure: None

Background 3rd generation IOL power calculation formulae incorporate constants SRK/ T: A constant Hoffer Q: predicted anterior chamber depth Holladay: surgeon factor Optimisation of these constants corrects systematic errors in predicted postoperative refraction However the process of optimisation is relatively complex perhaps discouraging many from doing so instead relying on values calculated by others

Purpose This single centre study set out to determine whether optimised IOL power calculation formulae differ between surgeons operating in the same unit

Method I Inclusion criteria Prospectively entered perioperative data (Medisoft electronic patient record) Implantation of L161AO Sofport or Akreos Fit (both Bausch & Lomb) intraocular lens (IOL) Surgeons implanting ≥100 of either IOL Preoperative IOLMaster (Carl Zeiss Meditec) biometry Postoperative subjective refraction Final corrected distance visual acuity ≥6/12 Exclusion criteria Combined surgery (e.g. phacovitrectomy) Complicated surgery

Method II For every eye and each of the Hoffer Q, Holladay and SRK/T formulae the constants predicting emmetropia were calculated using Freemat 3.6 Optimised constants calculated using the method recommended by Carl Zeiss Meditec Mean of personalised constants excluding values greater the 2 standard deviations from the overall population mean Statistical analysis R 2.8.2 (R Foundation for Statistical Computing) software used Differences between the manufacturers and optimised formula constants compared using the 2 sided paired t test Differences between surgeons compared using the ANOVA test p < 0.05 statistically significant

Results 6314 operations met inclusion criteria 4390 L161AO Sofport IOLs 15 surgeons 1924 Akreos Fit IOLs 4 surgeons No statistically significant differences between surgeons for optimised constants for any formula for either IOL type ANOVA test, all p >> 0.05

Nominal Holladay A Constant 118.0 Surgeon Surgeon Sofport AO Akreos Fit Nominal Holladay A Constant 118.0 Optimised SRK/T A Constant 118.69 * 118.45 * * paired t-test p < 0.05

Sofport AO Akreos Fit Nominal Hoffer Q pACD 4.97 Optimised pACD 5.12 * Surgeon Surgeon Sofport AO Akreos Fit Nominal Hoffer Q pACD 4.97 Optimised pACD 5.12 * 5.03 * * paired t-test p < 0.05

Nominal Holladay Surgeon Factor 1.22 Sofport AO Akreos Fit Nominal Holladay Surgeon Factor 1.22 Optimised SRK/T Surgeon Factor 1.67 * 1.51 * * paired t-test p < 0.05

Conclusions Like previous studies have shown, IOL power calculation formula constants optimised for the IOLMaster differ significantly from those recommended by the manufacturer However differences between surgeons operating in the same unit were not significant This reinforces the need for IOL constant optimisation and demonstrates that doing so is practical, even in large multisurgeon centres

Nathaniel KNOX CARTWRIGHT Contact Nathaniel KNOX CARTWRIGHT n.knoxcartwright@gmail.com