LASIK for High Myopia: New Considerations

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  • ADD SCAN OF TEXTBOOK COVER
  • Here are eight further examples of peripheral stromal thickening following high myopic LASIK
  • In my study using the MEL80, we compared the results of wavefront-guided treatments in a group of highly aberrated eyes with night vision disturbances against a control group of post refractive surgery eyes that were matched for preop myopia, but had been treated with a more modern aspheric ablation profile and were free of night vision problems.
  • In the control group, the spherical aberration was increased post-op, but the normalized contrast sensitivity was unchanged The repair group started with much higher levels of spherical aberration and significantly reduced contrast sensitivity. The wavefont-guided repair reduced spherical aberration enough to improve contrast sensitivity to normal levels….
  • … the fact that there was only a 27% reduction in the total spherical aberration. Assuming that the target would have been the level of spherical aberration in the control group, the wavefront-guided treatment achieved about a 50% reduction toward this level. Nevertheless, normalized contrast sensitivity returned to normal, implying that neural processing was doing the rest of the work for us. This study suggested that the threshold level for night vision disturbances to crop up was around 0.56 microns (analysed in a 6mm zone).
  • But, we were only getting about 20% effective correction for the amount of spherical aberration included in the repair treatment So, we knew that we would have to use a higher Z(4,0) value to get the desired effect of reducing the induction of spherical aberration in regular treatments
  • Riccar OSA
  • riccar
  • catbra
  • Munnerlyn 5 mm -6.00 For comparison, Aspheric 6 mm high myopic ablation (-7 to -9) – significantly less SA induction DZP 6 mm high myopic ablation (-7 to -9) – further reduction in SA induction In our study, found patients referred with NVDs had SA above 0.56 microns Ie -6 D Munnerlyn ablation induced this much SA for 4.9 mm pupil – so majority of patients would get NVDs Whereas, a -8 D ASA doesn’t reach this SA limit until a 6.15 mm pupil – so low myopes won’t get NVDs and high myopes will only get them if pupils >6.15 mm DZP has further increased the zone to a 6.60 mm pupil for a -8 D correction – so low myopes won’t get NVDs and high myopes will only get them if pupils >6.60 mm
  • Preop myopia -5.50 ou, Patient complains of diplopia in first week. Slow resolution over 2 weeks.
  • Preop myopia -5.00 ou. Note deep peripheral ablation. (dark blue inferior crescent)
  • LASIK for High Myopia: New Considerations

    1. 1. LASIK for high myopia: New considerations Dan Z Reinstein MD MA(Cantab) FRCSC FRCOphth 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, USA 4. Centre Hospitalier National d’Ophtalmologie, (Pr. Laroche) , Paris, France
    2. 2. First Results: Munnerlyn Ablation Profile <ul><li>Early ablation profiles often induced: </li></ul><ul><ul><li>Night Vision disturbances </li></ul></ul><ul><ul><li>Decreased contrast sensitivity </li></ul></ul><ul><li>Limited the range of treatable refractions </li></ul><ul><li>PROBLEM: Induction of spherical aberration </li></ul>Eur J Ophthalmol. 1994 Jan-Mar;4(1):43-51. Night vision after excimer laser photorefractive keratectomy: haze and halos. O'Brart DP, Lohmann CP, Fitzke FW, Smith SE, Kerr-Muir MG, Marshall J.
    3. 3. Ablation Profile Design: Larger Optical Zone Arch Ophthalmol. 1995 Apr;113(4):438-43. The effects of ablation diameter on the outcome of excimer laser photorefractive keratectomy. A prospective, randomized, double-blind study. O'Brart DP, Corbett MC, Lohmann CP, Kerr Muir MG, Marshall J. J Refract Corneal Surg. 1994 Mar-Apr;10(2):87-94. Excimer laser photorefractive keratectomy for myopia: comparison of 4.00- and 5.00-millimeter ablation zones. O'Brart DP, Gartry DS, Lohmann CP, Muir MG, Marshall J. Topography Wavefront Example: 5-mm Munnerlyn ablation for -6.00 D (1993 Summit Laser) Z(4,0) (OSA) 1.18 µm
    4. 4. Ablation Profile Design: Aspheric Profiles <ul><li>Barraquer 1980 </li></ul><ul><ul><li>Suggested parabolic keratomileusis </li></ul></ul><ul><li>Seiler 1993 – PRK aspheric profiles </li></ul><ul><ul><li>Less starburst & halos </li></ul></ul><ul><ul><li>Larger effective clear optical zone size </li></ul></ul>
    5. 5. Why was spherical aberration increasing?
    6. 6. <ul><li>Fluence correction: Topography </li></ul><ul><ul><li>Beam reflection compensation </li></ul></ul><ul><ul><li>Beam projection compensation </li></ul></ul>Optimization: Fluence correction J Refract Surg 2001;17(5):S584-7. Influence of corneal curvature on calculation of ablation patterns used in photorefractive laser surgery. Mrochen M, Seiler T.
    7. 7. Optimization <ul><li>Biomechanics </li></ul>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. JRS 2000; 16:407-413 VHF digital ultrasound
    9. 9. Examples of Peripheral Stromal Thickening Roberts C. The cornea is not a piece of plastic. Peripheral Stromal Thickening Central Flattening
    10. 10. Corneal Biomechanical Trade-off <ul><li>Hyperopic shift induced by </li></ul><ul><ul><li>Central flattening due to peripheral tissue removal </li></ul></ul><ul><li>Myopic shift induced by </li></ul><ul><ul><li>Epithelial thickening </li></ul></ul><ul><ul><li>Bowing of the back surface </li></ul></ul>Post-Op Pre-Op Back surface bowing Epithelial thickening
    11. 11. Free lunch?
    12. 12. ESCRS 2002, DZ Reinstein: Q-Slider
    13. 13. ESCRS 2002, DZ Reinstein: Q-Slider
    14. 14. ESCRS 2002, DZ Reinstein: Q-Slider
    15. 15. ESCRS 2002, DZ Reinstein: Q-Slider
    16. 16. ESCRS 2002, DZ Reinstein: Q-Slider
    17. 17. ESCRS 2002, DZ Reinstein: Q-Slider
    18. 18. Free Lunch? <ul><li>Increasing ablation zone diameter </li></ul><ul><li>Adding asphericity </li></ul><ul><li>Increases central ablation depth </li></ul><ul><li>No “Free Lunch” </li></ul>
    19. 19. 550 µm Pachymetry: Forces Compromise <ul><li>Modern aspheric ablation profiles still induce spherical aberration </li></ul><ul><li>Problem: high myopic corrections may result in NVDs </li></ul>
    20. 20. Wavefront-Guided Treatment of Spherical Aberration
    21. 21. How Effective are Wavefront Repair Treatments? Repair Group Complaining NVDs post LASIK Wavefront-Guided Repair Treatment Control Group Not Complaining NVDs post LASIK 16 eyes in study 4:1 matched for sphere & cyl <ul><li>Aberrations Pre-op </li></ul><ul><li>Aberrations Post-op </li></ul>Compare Aberrations <ul><li>Aberrations Pre-repair </li></ul><ul><li>Aberrations Post-repair </li></ul>
    22. 22. Correlation of Contrast with Wavefront <ul><li>Spherical Aberration </li></ul><ul><li>Contrast Sensitivity </li></ul>
    23. 23. Correlation of Contrast with Wavefront <ul><li>Spherical Aberration </li></ul><ul><li>Contrast Sensitivity </li></ul><ul><li>27% Gross Reduction </li></ul><ul><li>53% Net Reduction (cf tolerable level) </li></ul><ul><li>Tolerable level ~0.56 µm @ 6mm </li></ul>
    24. 24. Pre-Compensate for Spherical Aberration <ul><li>“ Q-slider” </li></ul><ul><ul><li>(WaveLight) </li></ul></ul><ul><li>Wavefront-guided ablation </li></ul><ul><ul><li>Includes pre-op spherical aberration </li></ul></ul><ul><ul><li>Effect dependent on pre-op spherical aberration </li></ul></ul><ul><li>Our Approach: Include an “artificial” wavefront </li></ul><ul><ul><li>Isolate spherical aberration: Z(4,0) as the only coefficient </li></ul></ul><ul><ul><li>Z(4,0) coefficient proportional to expected induction </li></ul></ul><ul><ul><li>Increase Z(4,0) coefficient: wavefront only 20% effective </li></ul></ul>
    25. 25. Patient 1, OD -7.13 D Corrected 6mm OSA Coma 0.04 µm Sph Ab 0.42 µm HO RMS 0.52 µm 6mm OSA Coma 0.09 µm Sph Ab 0.48 µm HO RMS 0.59 µm
    26. 26. Patient 1, OS -9.00 D Corrected 6mm OSA Coma 0.03 µm Sph Ab 0.49 µm HO RMS 0.57 µm 6mm OSA Coma 0.05 µm Sph Ab 0.55 µm HO RMS 0.60 µm
    27. 27. Patient 1, Night Vision Pre Op Post Op Rx Treated OD -6.50 -1.25 x 178 OS -8.25 -1.50 x 17
    28. 28. Induction of Spherical Aberration Complaint of NVD post RS 1 1
    29. 29. Limits to SA Pre-Compensation <ul><li>Excess spherical aberration pre-compensation can lead to “central islands” </li></ul>TMS WASCA (zonal) Epithelium OD
    30. 30. CENTRAL ISLANDS: Slides courtesy Gordon Balazsi, MD -5.50 D ablation Diplopia first week Slow resolution over 2 weeks
    31. 31. CENTRAL ISLANDS: Slides courtesy Gordon Balazsi, MD -5.00 D ablation
    32. 32. Differences in Ablation Depth
    33. 33. Ablation Depth with SA Pre-Compensation <ul><li>Including extra wavefront increases ablation depth </li></ul><ul><li>But, treatment of spherical aberration will also correct some sphere </li></ul>Unexpected Result: Greater over-correction than expected for larger Z(4,0) coefficients Consequence: Lower ablation depth than in theory
    34. 34. Ablation Depth with SA Pre-Compensation
    35. 35. New Profile for High Myopia <ul><li>Non-linear aspheric ablation profile: </li></ul><ul><ul><li>Increased peripheral ablation (not ↑ z(4,0)) </li></ul></ul><ul><ul><li>Reduced induction of spherical aberration </li></ul></ul><ul><ul><li>Free lunch: some myopia corrected due to central flattening </li></ul></ul><ul><ul><li>Extend this concept further to promote central flattening </li></ul></ul><ul><ul><li>Ability to correct high myopia without risk of NVDs </li></ul></ul>
    36. 36. New Profile: “Free Lunch” <ul><li>Over-corrected by +0.50 D compared with theory </li></ul><ul><li>Ablation depth lower than expected </li></ul>
    37. 37. Ablation Depth for New Profile
    38. 38. Femtosecond Lasers <ul><li>Femtosecond lasers have improved flap thickness reproducibility (VisuMax SD: 8 µm) </li></ul><ul><li>We can create thinner flaps (VisuMax: 80 µm) </li></ul><ul><li>Thinner flaps extends the range of myopia in LASIK </li></ul>Pre-release online
    39. 39. Outcomes
    40. 40. New Profile for High Myopia <ul><li>Patients </li></ul><ul><ul><li>Myopia SEQ -9.51 ± 1.32 D -8.00 up to -14.50 D </li></ul></ul><ul><ul><li>Myopia max merid -10.18 ± 1.48 D -8.00 up to -16.00 D </li></ul></ul><ul><ul><li>Cylinder -1.32 ± 1.10 D up to -6.25 D </li></ul></ul><ul><ul><li>220 eyes </li></ul></ul><ul><ul><li>1 year follow up </li></ul></ul><ul><li>Retreatments </li></ul><ul><ul><li>45% eyes treated as “two-stage” </li></ul></ul><ul><ul><li>Enhancement rate (non two-stage): 35% </li></ul></ul>
    41. 41. Advantages of Two Stage Procedure <ul><li>Increased safety </li></ul><ul><ul><li>Greater RST for primary treatment </li></ul></ul><ul><ul><li>Artemis measured RST to calculate retreatment </li></ul></ul><ul><ul><li>Option to retreat using topography-guided profile </li></ul></ul><ul><li>More accurate result </li></ul><ul><li>Patient has lower expectations </li></ul>
    42. 42. Topography Guided Retreatment Pre Post Reduced Sph Ab 0.48 µm 0.28 µm 41% HO RMS 0.72 µm 0.57 µm 21%
    43. 43. Example RST Planning Refraction -10.75 D sph Pachymetry 509 µm Flap Thickness (VisuMax) 80 µm Ablation Depth 135 µm Predicted RST 296 µm
    44. 44. MEL80 High Myopia: Accuracy
    45. 45. MEL80 High Myopia: Accuracy Within ±0.50 D 71% Within ±1.00 D 94%
    46. 46. Monocular Efficacy (excluding eyes not intended plano) n=176
    47. 47. n=176 98.3% Success Rate Pre Spectacle Corrected vs Post Uncorrected (excluding eyes not intended plano)
    48. 48. Pre Spectacle Corrected vs Post Uncorrected (excluding eyes not intended plano) n=176 41% Better Than Glasses
    49. 49. MEL80 High Myopia: Safety – BSCVA N=4 n=220
    50. 50. MEL80 High Myopia: Contrast Sensitivity * * Statistically significant (p<0.05)
    51. 51. Stability 3 Mo 6 Mo 12 Mo 24 Mo Pre-op 1 Day 1 Month 3 Months 6 Months 1 Year 2 Years Mean ±SD -9.60 ±1.39 +0.41 ±0.82 +0.01 ±0.82 -0.18 ±0.86 -0.22 ±0.91 -0.04 ±0.91 -0.06 ±1.07 # eyes 220 199 201 188 158 124 45
    52. 52. Take Home Message <ul><li>Know your spherical aberration induction per dioptre </li></ul><ul><li>Measure pre-op spherical aberration </li></ul><ul><li>Check whether spherical aberration is going to go beyond the threshold </li></ul><ul><ul><li>Use SA pre-compensation </li></ul></ul><ul><ul><li>Use a 2-stage procedure (wavefront / topography guided repair if necessary as second treatment) </li></ul></ul><ul><li>Caution with predicted RST </li></ul><ul><ul><li>Reduce potential errors </li></ul></ul><ul><ul><li>Measure pachymetry with high repeatability instrument </li></ul></ul><ul><ul><li>Use high reproducibility flap creation technique </li></ul></ul><ul><ul><li>Always include flap thickness bias </li></ul></ul>
    53. 53. LASIK for high myopia: New considerations Dan Z Reinstein MD MA(Cantab) FRCSC FRCOphth 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, USA 4. Centre Hospitalier National d’Ophtalmologie, (Pr. Laroche) , Paris, France Thank You
    54. 54. Topography Guided Retreatment Pre Post Reduced Sph Ab 0.48 µm 0.28 µm 41% HO RMS 0.72 µm 0.57 µm 21%
    55. 55. Benefit of Aspheric-WF over Aspheric Spherical Aberration Z4,0 -50% -50% -50% -50%

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