Very high myopic LASIK using new hybrid aspheric profiles 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
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Very high myopic LASIK using new hybrid aspheric profiles
Dan Z Reinstein MD MA(Cantab) FRCSC FRCOphth1,2,3,4
1. London Vision Clinic, London, UK 2. St. Thomas’ Hospital - Kings College, London, UK 3. Weill Medical College of Cornell University, New York, USA4. Centre Hospitalier National d’Ophtalmologie, (Pr. Laroche) , Paris, France
• Early ablation profiles often induced:– Night Vision disturbances– Decreased contrast sensitivity
• Limited the range of treatable refractions• PROBLEM: Induction of spherical aberration
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.
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
Z(4,0) (OSA)
1.18 µm
Example: 5-mm Munnerlyn ablation for -6.00 D (1993 Summit Laser)
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.
Correlation of Contrast with WavefrontSpherical Aberration Contrast Sensitivity
• 27% Gross Reduction
• 53% Net Reduction (cf tolerable level)
• Tolerable level ~0.56 µm @ 6mm
Vorführender
Präsentationsnotizen
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….
• Wavefront-guided ablation– Includes pre-op spherical aberration– Effect dependent on pre-op spherical aberration
• Our Approach: Include an “artificial” wavefront– Isolate spherical aberration: Z(4,0) as the only coefficient– Z(4,0) coefficient proportional to expected induction– Increase Z(4,0) coefficient: wavefront only 20% effective
Vorführender
Präsentationsnotizen
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
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
• Non-linear aspheric ablation profile:– Increased peripheral ablation (not ↑ z(4,0))– Reduced induction of spherical aberration– Free lunch: some myopia corrected due to central
flattening
Extend this concept further to promote central flatteningAbility to correct high myopia without risk of NVDs
• Patients– Myopia SEQ -9.51 ± 1.32 D -8.00 up to -14.50 D– Myopia max merid -10.18 ± 1.48 D -8.00 up to -16.00 D– Cylinder -1.32 ± 1.10 D up to -6.25 D– 220 eyes– 1 year follow up
• Increased safety– Greater RST for primary treatment– Artemis measured RST to calculate retreatment– Option to retreat using topography-guided profile
• More accurate result• Patient has lower expectations
• Know your spherical aberration induction per dioptre• Measure pre-op spherical aberration• Check whether spherical aberration is going to go
beyond the threshold– Use SA pre-compensation– Use a 2-stage procedure (wavefront / topography guided
repair if necessary as second treatment)• Caution with predicted RST
– Reduce potential errors– Measure pachymetry with high repeatability instrument– Use high reproducibility flap creation technique– Always include flap thickness bias
Very high myopic LASIK using new hybrid aspheric profiles
Dan Z Reinstein MD MA(Cantab) FRCSC FRCOphth1,2,3,4