The Pathophysiology of Regression Following LASIK

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The Pathophysiology of Regression Following LASIK

  1. 1. The Pathophysiology of Regression Following LASIK Dan Z Reinstein MD MA(Cantab) FRCSC DABO 1,2,3,4 1. London Vision Clinic, London, UK 2. St. Thomas’ Hospital - Kings College, London, UK 3. Weill Medical College of Cornell University, New York, 4. Centre Hospitalier National d’Ophtalmologie, (Pr.Laroche), Paris
  2. 2. The author acknowledge a financial interest in the subject matter of this presentation. Many aspects of the Artemis™ technology are patented. Patents are administered by the Cornell Research Foundation . This intellectual property has been licensed by Cornell to Ultralink, LLC ., a company in which the authors have a financial interest.
  3. 3. Regression following LASIK <ul><li>“ Regression” </li></ul><ul><ul><li>Not a diagnosis but an observation </li></ul></ul><ul><ul><li>Produced by unpredicted biomechanical and/or epithelial changes </li></ul></ul>
  4. 4. The Accuracy of Routine LASIK; Isolation of Biomechanical and Epithelial Factors Dan Z Reinstein, MD, MA(Cantab), FRCSC Sabong Srivannaboon, MD Ronald H Silverman, PhD D Jackson Coleman, MD Weill Medical College of Cornell University, NY, NY Lasik Vision Corporation, Vancouver Canada Service V, Centre Hopitalier National d’Ophtalmologie des XV-XV. Paris, France Mahidol University, Bangkok Thailand ARVO 2000
  5. 5. “ Artemis 2” by Ultralink LLC <ul><li>50 MHz Arc-Scan </li></ul><ul><li>Meridional sweep ( 0.4sec) : </li></ul><ul><ul><li>Whole anterior segment </li></ul></ul><ul><ul><li>Whole Cornea </li></ul></ul><ul><li>Scan positional control </li></ul><ul><ul><li>IR video-image of eye </li></ul></ul><ul><ul><li>Corneal light-reflex </li></ul></ul><ul><ul><li>Internal fixation targets </li></ul></ul><ul><li>Exam time: 3-min per eye </li></ul>www.ArcScan.com FDA approved 2000
  6. 6. VHF Digital Ultrasound <ul><li>Cornell University prototype </li></ul><ul><ul><li>50 MHz probe enhanced by digital signal processing </li></ul></ul><ul><ul><li>Pachymetric precision = 1.0 microns </li></ul></ul><ul><ul><li>Meridional scans for 3D data set of individual corneal interfaces </li></ul></ul><ul><ul><li>3D pachymetric topography </li></ul></ul>
  7. 7. VHF Digital Ultrasound
  8. 8. Artemis C12 Display Reinstein et al. Journal of Refractive Surgery 2000 Jul-Aug;16:414-30 Roberts C. The cornea is not a piece of plastic.
  9. 9. Deformation of the Cornea - Distinction <ul><li>Mechanical deformation </li></ul><ul><ul><li>Stable (?) elastic “bulge” </li></ul></ul><ul><li>Ectasia </li></ul><ul><ul><li>Progressive plastic deformity </li></ul></ul>
  10. 10. Deformation of the Cornea - Distinction <ul><li>Mechanical deformation </li></ul><ul><ul><li>Stable (?) elastic “bulge” </li></ul></ul><ul><li>Ectasia </li></ul><ul><ul><li>Progressive plastic deformity </li></ul></ul>
  11. 11. Deformation of the Cornea - Distinction <ul><li>Mechanical deformation </li></ul><ul><ul><li>Stable (?) elastic “bulge” </li></ul></ul><ul><li>Ectasia </li></ul><ul><ul><li>Progressive plastic deformity </li></ul></ul>
  12. 12. Method <ul><li>52 eyes </li></ul><ul><li>Routine LASIK </li></ul><ul><ul><li>Myopia: - 1.00 to -10.25 [ mean (SD) -4.44 (2.32) ] </li></ul></ul><ul><ul><ul><li>Hansatome/Moria LSK One </li></ul></ul></ul><ul><ul><ul><li>Nidek EC5000/Technolas 217 </li></ul></ul></ul><ul><li>Pre- and post-operative ≥ 3 months </li></ul><ul><ul><li>Orbscan, (Orbtek/Bausch&Lomb Inc.) </li></ul></ul><ul><ul><li>VHF 3D Digital Ultrasound scanning - Artemis™ </li></ul></ul>
  13. 13. Calculated Total Corneal Power <ul><li>Pre-op </li></ul><ul><ul><li>Front </li></ul></ul><ul><ul><li>Bowman’s </li></ul></ul><ul><ul><li>Back </li></ul></ul>Orbscan Orbscan front + VHF Ultrasound Thickness
  14. 14. Calculated Total Corneal Power <ul><li>Pre-op </li></ul><ul><ul><li>Front </li></ul></ul><ul><ul><li>Bowman’s </li></ul></ul><ul><ul><li>Back </li></ul></ul>Calculated Corneal Power
  15. 15. <ul><li>Post-LASIK </li></ul>Calculated Corneal Power Orbscan Orbscan front + VHF Ultrasound Thickness Post-LASIK-epithelial hyperplasia Post-LASIK “bowing”
  16. 16. <ul><li>Post-LASIK </li></ul>Calculated Corneal Power Calculated Corneal Power
  17. 17. Calculated Corneal Power <ul><li>Post-LASIK - no “epithelial” effect </li></ul><ul><ul><li>Use pre-operative epithelium </li></ul></ul>Post-LASIK-epithelial hyperplasia Post-LASIK “bowing”
  18. 18. Calculated Corneal Power <ul><li>Post-LASIK - no “epithelial” effect </li></ul><ul><ul><li>Use pre-operative epithelium </li></ul></ul>Substitute with pre-epithelium Post-LASIK “bowing”
  19. 19. Calculated Corneal Power <ul><li>Post-LASIK - no “epithelial” effect </li></ul><ul><ul><li>Use pre-operative epithelium </li></ul></ul>Substitute with pre-epithelium Post-LASIK “bowing” Calculated Corneal Power
  20. 20. Calculated Corneal Power <ul><li>Post-LASIK - no “bowing” </li></ul><ul><ul><li>Subtract back surface radius change from all surfaces </li></ul></ul>Subtract “bowing” Post-LASIK “ bowing ” Post-LASIK-epithelial hyperplasia
  21. 21. Calculated Corneal Power <ul><li>Post-LASIK - no “bowing” </li></ul><ul><ul><li>Subtract back surface radius change from all surfaces </li></ul></ul>Subtract “bowing” from all three surfaces
  22. 22. Calculated Corneal Power <ul><li>Post-LASIK - no “bowing” </li></ul><ul><ul><li>Subtract back surface radius change from all surfaces </li></ul></ul>Calculated Corneal Power
  23. 23. Calculated Corneal Power <ul><li>Post-LASIK - no epithelial or “bowing” effects </li></ul><ul><ul><li>Subtract back surface radius change from all surfaces </li></ul></ul><ul><ul><li>Use pre-operative epithelium </li></ul></ul>
  24. 24. Calculated Corneal Power <ul><li>Post-LASIK - no epithelial or “bowing” effects </li></ul><ul><ul><li>Subtract back surface radius change from all surfaces </li></ul></ul><ul><ul><li>Use pre-operative epithelium </li></ul></ul>Subtract “bowing”
  25. 25. Calculated Corneal Power <ul><li>Post-LASIK - no epithelial or “bowing” effects </li></ul><ul><ul><li>Subtract back surface radius change from all surfaces </li></ul></ul><ul><ul><li>Use pre-operative epithelium </li></ul></ul>Subtract “bowing”
  26. 26. Calculated Corneal Power <ul><li>Post-LASIK - no epithelial or “bowing” effects </li></ul><ul><ul><li>Subtract back surface radius change from all surfaces </li></ul></ul><ul><ul><li>Use pre-operative epithelium </li></ul></ul>Substitute pre-op epithelial layer Subtract “bowing”
  27. 27. Calculated Corneal Power <ul><li>Post-LASIK - no epithelial or “bowing” effects </li></ul><ul><ul><li>Subtract back surface radius change from all surfaces </li></ul></ul><ul><ul><li>Use pre-operative epithelium </li></ul></ul>Substitute pre-op epithelial layer Subtract “bowing”
  28. 28. Calculated Corneal Power <ul><li>Post-LASIK - no epithelial or “bowing” effects </li></ul><ul><ul><li>Subtract back surface radius change from all surfaces </li></ul></ul><ul><ul><li>Use pre-operative epithelium </li></ul></ul>Substitute pre-op epithelial layer Subtract “bowing” Calculated Corneal Power
  29. 29. Methods: Outcome Measures <ul><li>Outcome Measures </li></ul><ul><li>Magnitude </li></ul><ul><ul><li>Epithelial </li></ul></ul><ul><ul><li>Biomechanical effects </li></ul></ul><ul><li>Proportional effect </li></ul><ul><li>Correlation between </li></ul><ul><ul><li>[ manifest achieved effect ] vs. [ calculated achieved effect – epithelial effect ] </li></ul></ul><ul><ul><li>[ manifest achieved effect ] vs. [ calculated achieved effect – biomechanical effect ] </li></ul></ul><ul><ul><li>[ manifest achieved effect ] vs. [ calculated achieved effect – epithelial effect – biomechanical effect ] </li></ul></ul>
  30. 30. Magnitude of Post-Operative Epithelial and Biomechanical Changes p <0.0005
  31. 31. Results - Accuracy of Treatment <ul><li>Attempted vs. Achieved (by refraction) </li></ul>
  32. 32. Validation <ul><li>Change in Power of the cornea (CPC) Calculation </li></ul><ul><ul><li>Correlation of corneal power change by calculation, with refractive change observed </li></ul></ul>
  33. 33. Removing Epithelial Effect <ul><li>Correlation of corneal power change by calculation, with refractive change observed </li></ul><ul><ul><li> epithelium </li></ul></ul><ul><ul><li> “ bowing” </li></ul></ul><ul><ul><li> epithelium  ”bowing” </li></ul></ul>
  34. 34. Removing Bowing Effect <ul><li>Correlation of corneal power change by calculation, with refractive change observed </li></ul><ul><ul><li> epithelium </li></ul></ul><ul><ul><li> “ bowing” </li></ul></ul><ul><ul><li> epithelium  ”bowing” </li></ul></ul>
  35. 35. Removing Epithelial + Bowing Effects <ul><li>Correlation of corneal power change by calculation, with refractive change observed </li></ul><ul><ul><li> epithelium </li></ul></ul><ul><ul><li> “ bowing” </li></ul></ul><ul><ul><li> epithelium  “bowing” </li></ul></ul>
  36. 36. Impact of Epithelial and Bowing Effects on Accuracy of LASIK
  37. 37. The Epithelium in LASIK
  38. 38. Effect of Epithelial Changes on Refractive Outcome in LASIK Sabong Srivannaboon, MD Dan Z Reinstein, MD, FRCSC Hugo FS Sutton, MD, FRCSC Ronald H Silverman, Simon P Holland, MD, FRCSC D. J. Coleman, MD, FACS University of British Columbia, Vancouver, BC Canada Weill Medical College of Cornell University, New York, NY ARVO 1999
  39. 39. Epithelium: Results <ul><li>Change in Power </li></ul><ul><li>Change in Thickness </li></ul>
  40. 40. <ul><li>3 groups: Low, Moderate, High myopia </li></ul><ul><li>Changes of the epithelial thickness were determined annularly for the: </li></ul><ul><ul><li>Center </li></ul></ul><ul><ul><li>Anulus at zone diameters of : </li></ul></ul><ul><ul><ul><li>3,4,5,6 and 7 mm </li></ul></ul></ul>Methods
  41. 41. Epithelial Power Changes and Postop SE Error
  42. 42. Epithelial Profile Changes
  43. 43. Results Low Moderate High
  44. 44. Central and Epithelial Profile Changes Figure 5
  45. 45. Hypothesis: Epithelial Thickening End
  46. 46. Epithelial Power Change vs. Myopia Treated
  47. 47. Epithelial Power Change vs. Myopia Treated
  48. 48. What do we do about regression nowadays? <ul><li>Enhance! </li></ul><ul><li>But we should diagnose regression before treating </li></ul><ul><ul><li>epithelial or biomechanical? </li></ul></ul>
  49. 49. Undercorrected LASIK <ul><li>43 yo white female </li></ul><ul><li>OD OS </li></ul><ul><li>Pre op refraction -6.00 -0.50 x 115 -6.00 -0.50 x 20 </li></ul><ul><li>Corneal thickness </li></ul><ul><ul><li>(Orbscan) 542 540 </li></ul></ul><ul><ul><li>(Sonogage) 537 553 </li></ul></ul><ul><li>Flap thickness (Hansatome) 160 160 </li></ul><ul><li>Ablation depth (MEL70) 99 99 </li></ul><ul><li>Predicted residual bed 278 281 </li></ul><ul><li>Post op (3mo) UCVA 20/20 20/25 </li></ul><ul><li>Post op (6 mo) UCVA 20/25 20/25 </li></ul><ul><li>-0.50 -0.50 x 150 -0.75 -0.50 x 145 </li></ul><ul><li> (20/16) (20/16) </li></ul>
  50. 50. Undercorrected LASIK : To enhance OD? <ul><li>Predicted RST = 278 µm </li></ul><ul><li>Ablation depth required = 24 µm </li></ul><ul><li>278 – 24 = 254 µm </li></ul>277 μ m
  51. 51. Undercorrected LASIK : To enhance OS? <ul><li>Predicted RST = 281 µm </li></ul><ul><li>Ablation depth required = 27 µm </li></ul><ul><li>294 – 27 = 254 µm </li></ul><ul><li>Enhancement OD only! </li></ul>218 μ m 191–µm
  52. 52. Summary: Pathophysiology of Regression <ul><li>“ Regression” is not a diagnosis, but an observation . </li></ul><ul><li>Epithelial and biomechanical changes account for LASIK inaccuracy </li></ul><ul><li>The diagnosis of “regression” can only be made by layered analysis of the cornea after LASIK </li></ul><ul><li>Given the uncertainty in pre–op corneal thickness and flap thickness, direct measurement of flap and residual stromal thickness before enhancement will maximize safety. </li></ul>
  53. 53. Summary: caution <ul><li>Beware of wavefront guided enhancements for decreasing spherical aberration (“expanding the optical zone”) - they are very tissue intensive, and you may have less tissue available than expected. </li></ul>

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