Optimization of IOL Power Calculation Constants - ASCRSASOA 2010

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Optimization of IOL Power Calculation  Constants - ASCRSASOA 2010 Powered By Docstoc
					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
• 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
• 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
• 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
       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 < 0.05
  Surgeon                                    Surgeon

                       Sofport AO   Akreos Fit
Nominal Hoffer Q pACD 4.97          4.97
        Optimised pACD 5.12 *       5.03 *

                                       * paired t-test p < 0.05
           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 < 0.05

• 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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