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IOL Power Calculation in Normal Eyes

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IOL Power Calculation in Normal Eyes

  1. 1. A.H. Mirfendereski Tehran University of Medical Sciences Optometry Department
  2. 2. Pre-IOL era :  Patients traded in their cataractous lenses for “Coke bottle bottom” spectacles.  Problems :  Prismatic effect and ring scotoma between 40 and 60 degrees.  Markedly constricted visual field.  Lack of stereopsis.  Spherical aberrations.  False orientation.  As early as the 1760s, ophthalmologists had explored the idea of an artificial replacement for the cataractous lens.  Around 1795, Casamata inserted a glass lens into an eye, but it immediately sank back toward the posterior pole.
  3. 3. IntroductionIntroduction  Sir Harold Ridley was the first to successfully implant an intraocular lens in 1949. The procedure was performed on a 45-year-old woman at St Thomas Hospital at London.  That first IOL was manufactured by the Rayner company from PMMA.  The surgery was an anatomic success, but the patient was left highly myopic.  Her postoperative visual acuity was 6/18, requiring a refractive correction of -18.0 -6.0 × 120. There was clearly an error in the calculation.  Baron designed and implanted the first Anterior Chamber IOL (ACIOL) in 1952.
  4. 4. IntroductionIntroduction
  5. 5. Clinical historyClinical history MethodMethod  Before 1975 the power of an IOL was calculated by the use of this equation : P = 18 + ( 1.25 × Ref )  Errors exceeding 1 diopter occurred in over 50% of cases.  These large errors were caused by the difficualty of determining the patients' refractive error,
  6. 6. Power CalculationPower Calculation FormulasFormulas
  7. 7. Basic opticsBasic optics
  8. 8. Basic opticsBasic optics In a two-lens System, the object for the second lens is the image for the first lens. cL n P cv n − =+ − c K n n cL n P − − − =
  9. 9. Original TheoriticalOriginal Theoritical FormulasFormulas Required Measurements :  L : The Axial Length in millimeters.  C : The estimated postoperative anterior chamber depth (ACD) in millimeters.  K: The corneal power in diopters.  r : The corneal radius of curvature.
  10. 10. Original RegressionOriginal Regression FormulasFormulas  Regression formulas are derived empirically from retrospective computer analysis of data accured on a great many patients. A regression formula is based on this equation : P = A – BL – CK L: Axial Length (millimeters) K: Corneal Power (diopters) A,B,C: Constants  SRK I is the most popular original regression formula : P = A – 2.5L – 0.9K
  11. 11. Modified FormulasModified Formulas 1000 05.0336.1 336.1 05.0 1336 + − + − −− = C RK CL P 1336 05.00125.1 1 05.0)23(1.0 1336 + − − −−−− = C K CLL P
  12. 12. Modified FormulasModified Formulas )4)(( )4(1336 CRCL LR P −− − = KLAP 9.05.21 −−=
  13. 13. Modified FormulasModified Formulas
  14. 14. Estimated Lens PositionEstimated Lens Position (ELP)(ELP)
  15. 15. Estimated Lens PositionEstimated Lens Position (ELP)(ELP) (1/23.45)12.5LengthAxialAG )]4/1)((AGR[R0.56aACD SaACDELP 222 ××= −+= += − 3.595-0.9704)value(ACDfactorS 65.60-0.5663)constant-(AfactorS ×= ×=
  16. 16. The Haigis FormulaThe Haigis Formula )()( positionlenseffectivethe 210 ALaACDaad d ×+×+= =
  17. 17. Measuring The Axial LengthMeasuring The Axial Length
  18. 18. A-SCANA-SCAN
  19. 19. A-SCANA-SCAN Community Eye Health Journal Vol. 19 No. 60 DECEMBER 2006 www.cehjournal.org J Emmetropia 2011; 2: 210-216 ©2011 SECOIR - Sociedad Española de Cirugía Ocular Implanto-Refractiva
  20. 20. A-SCANA-SCAN
  21. 21. IOL MasterIOL Master
  22. 22. IOL MasterIOL Master IOL MasterIOL Master LenstarLenstar
  23. 23. 1.1. IOL Power CalculationsIOL Power Calculations, H. John Shammas, SLACK, H. John Shammas, SLACK Incorporated, 2004Incorporated, 2004 2.2. Intraocular Lenses in Cataract and RefractiveIntraocular Lenses in Cataract and Refractive SurgerySurgery,, Dimitri T. Azar. W.B. Saunders Company 2001Dimitri T. Azar. W.B. Saunders Company 2001 3.3. Lens Implant Power CalculationLens Implant Power Calculation, John A. Retzlaff,, John A. Retzlaff, Slack Incorporated, 1990Slack Incorporated, 1990

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