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

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Optimization of IOL Power Calculation Constants
By Unit or by Surgeon?
Poster Number P90
Category Intraocular Surgery (Cataract and
Refractive)

• Nathaniel E Knox Cartwright, MA, MRCOphth
• Bristol Eye Hospital, Bristol, UK

Financial Disclosure None
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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

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Purpose

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

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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

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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 lt 0.05 statistically significant

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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 gtgt 0.05

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Surgeon
Surgeon
Sofport AO Akreos Fit
Nominal Holladay A Constant 118.0 118.0
Optimised SRK/T A Constant 118.69 118.45
paired t-test p lt 0.05
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Surgeon
Surgeon
Sofport AO Akreos Fit
Nominal Hoffer Q pACD 4.97 4.97
Optimised pACD 5.12 5.03
paired t-test p lt 0.05
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Surgeon
Surgeon
Sofport AO Akreos Fit
Nominal Holladay Surgeon Factor 1.22 1.22
Optimised SRK/T Surgeon Factor 1.67 1.51
paired t-test p lt 0.05
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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

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Contact

• Nathaniel KNOX CARTWRIGHT
• n.knoxcartwright_at_gmail.com