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Optimization of IOL Power Calculation Constants: By Unit or by Surgeon?

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

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Optimization of IOL Power Calculation Constants: By Unit or by Surgeon?

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

  2. 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

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

  4. 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

  5. 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

  6. 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

  7. Surgeon Surgeon * paired t-test p < 0.05

  8. Surgeon Surgeon * paired t-test p < 0.05

  9. Surgeon Surgeon * paired t-test p < 0.05

  10. 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

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

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