1. 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

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

8. 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

9. 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

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. Nathaniel KNOX CARTWRIGHT
Contact
Nathaniel KNOX CARTWRIGHT