IOL Power Calculation in Post-Refractive Patients

1. IOL Power Calculation in Post-Refractive Patients Cesar Ramon G. Espiritu, MD Benjamin G. Cabrera, MD Richard C. Kho, MD Joanne G. Bolinao, MD

2. IOL Calculation in Post-Refractive Patients Increasing because of popularity of refractive surgery Patients who had refractive surgery will soon need cataract surgery

3. Concern of Cataract Surgeons Poor predictability and accuracy of IOL calculation Wrong corneal power measurement Flattened anterior cornea Keratometry reads a falsely large area Index of refraction of cornea is probably changed -Warren Hill, MD

4. Solution Refraction derived keratometric value Clinical History Method Does not eliminate hyperopic results although their magnitude is less -Gimbel HV, Sun R, Furlong MT, et al Accuracy and Predictability of intraocular lens power calculation after LASIK. J Cataract Refract Surg 2001;27:571-576

5. Refraction Derived K�s Clinical History Method Spherical Equivalent at Corneal plane Kpost-R= Kpre-R + Rpre-R � Rafter R

6. IOLMaster

7. Refraction Derived Espiritu Formula IOL = IOLPRE-RS+ (Pre-RS SE � Post-RS SE) X

8. Which one is more accurate? Espiritu formula vs. Clinical History Method (CHM) What if Refractive history is not available? Latest K Adjusted K Contact Lens Method

9. Objectives To compare the accuracy of IOL calculation in post-refractive patients by Espiritu Method vs. Clinical History Method To compare the results of 2 different IOL formulas (SRK-T vs Haigis) To determine the difference of the latest keratometry with the refractive derived keratometry

10. Patients and Methods 18 post-refractive and post-phaco eyes 15 �LASIK, 2- PRK and 1-RK Refractive surgery done by single surgeon Phaco done by single surgeon IOL calculation: Attempted vs. Achieved Latest K Clinical History Method Corneal Plane (IOLMaster) Espiritu formula

11. RESULTS

12. mean age for cataract surgery was 44.5 SD + 14.85 (Range 34-77) MRSE before refractive surgery -8.935 Dsph SD+7.16 (Range -2.25 to -22.5) MRSE post refractive surgery -0.25 Dsph SD +1.75 (Range 2.00Dsph to -5.25) 20/30 better MRSE before cataract surgery -1.12 Dsph MRSE after cataract surgery 0.23Dsph SD+ 1.18 (Range -1.75 to 1.87)

13. UCVA: Post Refractive and Post-Phaco

14. BCVA Post-Refractive and Post Phaco

16. Espritu Formula R2 =0.69n= 15

17. Clinical History Method R2 =0.61n=15

18. Logic Behind the Espiritu Formula

19. Espiritu Formula CHM R2 =0.69 mean error from attempted refraction of 0.028 + 1.10 Typical highest IOL value Least likely to result in a post-operative hyperopic surprise R2 =0.61 mean error from attempted refraction of 0.074 + 0.90 Recommended by most studies May still end up with post-op hyperopic surprise

20. Which K to use? Difference of CHM K spectacle and CHM K corneal plane 0.57 SD +0.4 Difference of Latest K and CHM K corneal plane 1.18 + 0.86

21. Refractive History NOT known Adjusted K = Latest K � 1 Corneal Topography = average of topographic values obtained within the 3.0mm zone Contact Lens Method KCL= BC + D + (ORCL �MR)

22. Adjusted K Difference of Latest K and CHM K plane =1.18 + 0.86 Recommended in patients post RK especially if optic zone is 4mm or larger Jack Holladay, MD IOL Calculation for Unusual Eyes Chapter 15. In: Gills JP, ed. Cataract Surgery: The State of Art. Thorofare, NJ: Slack: 1998 Recommended in patients when refractive data is not known Argento C MD, Cosentino MJ MD, Badoza D MD Intraocular Lens Power Calculation after Refractive Surgery. J Cataract and Refract Surg 2003; 29:1346-1351 Gimbel HV, Sun, R, Furlong MT, et Al. Accuracy and Predictability of intraocular lens power calculation after photorefractive surgery. J Cataract and Refract Surg 2000; 26: 1147-1151

23. Adjusted K

24. Contact Lens Method Patients whose cataract does not prevent them from being refracted to + 0.5 D If visual acuity is at least 20/80 KCL= BC + D + (ORCL �MR) Base curve is stronger/weaker than cornea by the amount of the shift Myopic Shift = Stronger Hyperopic Shift = Weaker Myopia may be due to the Nuclear Sclerosis

25. Corneal Topography Average of K�s within the 3 mm zone Zeiss Humphrey Atlas topographer or the EyeSys Corneal Analysis System Modified Maloney Method (CcpX 1.11) � 5.55 = K Post-operative Regression Method (CcpX1.23) � 10.41 =K

26. Which IOL Formula Fourth Generation formulae Holladay 2 Haigis Third Generation formulae Holladay 1 Hoffer Q SRK/T

27. CHM using SRK-T R2=0.07

28. SRK-T Most 2 variable formula such as SRK/T, assume that the anterior and posterior segments of the eye are proportional Use axial length and K to estimate ELP Will assume a falsely shallow ELP Recommend less IOL power Post-operative Hyperopia

29. Third Generation IOL Formulae Good for axial length between 22mm to 25mm Good for corneal powers between 42 D and 46 D

30. Summary Espiritu Method and Clinical History method would give the best estimated IOL power post-refractive patients CHM K computed at corneal plane is recommended Use 4th generation IOL formula preferably Holladay 2, Haigis Adjusted K method or Corneal Topography method if refractive history is not available

31. Use as many formulae as you can The Espiritu method will typically suggest the highest the IOL power No lens exchange should be contemplated until after the first post-operative week or until the refraction has stabilized, whichever is longer. With increasing number of patients having already undergone keratorefractive surgery, the numbers of these patients coming to cataract surgery in the next few years will be significant Simple and accurate methods of determining corneal power become increasingly important