high myopia final czm dubai_2011

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

©DZ Reinstein [email protected]

First Results: Munnerlyn Ablation Profile

• 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.


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

Z(4,0) (OSA)

1.18 µm

Example: 5-mm Munnerlyn ablation for -6.00 D (1993 Summit Laser)


Ablation Profile Design: Aspheric Profiles

• Barraquer 1980– Suggested parabolic keratomileusis

• Seiler 1993 – PRK aspheric profiles– Less starburst & halos– Larger effective clear optical zone size

Vorführender

Präsentationsnotizen

ADD SCAN OF TEXTBOOK COVER

Why was spherical aberration increasing?


• Fluence correction: Topography– Beam reflection compensation– Beam projection compensation

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.


Optimization

• Biomechanics

VHF digital ultrasound


Artemis C12 Display Reinstein et al. Journal of Refractive Surgery2000 Jul-Aug;16:414-30

Roberts C. The cornea is not a piece of plastic.JRS 2000; 16:407-413

VHF digital ultrasound


Examples of Peripheral Stromal Thickening

Roberts C. The cornea is not a piece of plastic.

Peripheral Stromal Thickening

Central Flattening

Vorführender


Here are eight further examples of peripheral stromal thickening following high myopic LASIK


Corneal Biomechanical Trade-off

• Hyperopic shift induced by– Central flattening due to peripheral tissue removal

• Myopic shift induced by– Epithelial thickening– Bowing of the back surface

Post-Op

Pre-Op

Back surface bowing

Epithelial thickening

Free lunch?


ESCRS 2002, DZ Reinstein: Z4,0-Slider (aka Q-slider)


Free Lunch?

• Increasing ablation zone diameter• Adding asphericity

• Increases central ablation depth

• No “Free Lunch”


550 µm Pachymetry: Forces Compromise

• Modern aspheric ablation profiles still induce spherical aberration

• Problem: high myopic corrections may result in NVDs

y = -0.059x - 0.0136R² = 0.6444

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

-10.00-9.00-8.00-7.00-6.00-5.00-4.00-3.00-2.00-1.000.00

Attempted Spherical Equivalent vs. Change in Z(4,0) CoefficientASA Treatments

Attempted Spherical Equivalent (Diopters)

Change in Z(4,0) Coefficient (µm, OSA)

Wavefront-Guided Treatment of Spherical Aberration


Control Pre Control Post Pre CRS-M Repair

Post CRSM-Repair

Sph Ab Area 122 276 563 410

0100200300400500600700800900

µm

2

p

3 cpd 6 cpd 12 cpd 18 cpdControl Pre 1.02 1.02 1.03 1.04Control Post 1.04 1.01 1.03 1.01Pre CRSM-Repair 0.85 0.84 0.77 0.75Post CRSM-Repair 1.04 1.02 1.02 1.00

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

Normalized Contrast

Sensitivity Ratio

Correlation of Contrast with WavefrontSpherical Aberration Contrast Sensitivity

• 27% Gross Reduction

• 53% Net Reduction (cf tolerable level)

• Tolerable level ~0.56 µm @ 6mm

Vorführender


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….


Pre-Compensate for Spherical Aberration

• “Q-slider”– (WaveLight)

• 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


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


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

Vorführender


Riccar OSA


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

Vorführender


riccar


Patient 1, Night Vision

Rx TreatedOD -6.50 -1.25 x 178

OS -8.25 -1.50 x 17

Pre Op Post Op

Vorführender


catbra


Induction of Spherical Aberration

Complaint of NVD post RS1

1

Vorführender


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


Limits to SA Pre-Compensation

• Excess spherical aberration pre-compensation can lead to “central islands”

TMS WASCA (zonal) Epithelium

OD


CENTRAL ISLANDS:

Slides courtesy Gordon Balazsi, MD

-5.50 D ablationDiplopia first weekSlow resolution over 2 weeks

Vorführender


Preop myopia -5.50 ou, Patient complains of diplopia in first week. Slow resolution over 2 weeks.


CENTRAL ISLANDS:

Slides courtesy Gordon Balazsi, MD

-5.00 D ablation

Vorführender


Preop myopia -5.00 ou. Note deep peripheral ablation. (dark blue inferior crescent)


Ablation Depth with SA Pre-Compensation

Vorführender


Take out the NLA theory Check the munnerlyn depths – should be 12 um per D?


New Profile for High Myopia

• 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

Roberts C. The cornea is not a piece of plastic.

Peripheral Stromal Thickening

Central Flattening


New Profile: “Free Lunch”

• Over-corrected by +0.50 D compared with theory• Ablation depth lower than expected

y = 0.9958x - 0.5106R² = 0.9291

-14

-13

-12

-11

-10

-9

-8

-7

-6

-5-14-13-12-11-10-9-8-7-6

Attempted vs. Achieved Spherical Equivalent


Achieved Spherical Equivalent (Diopters)


Ablation Depth for New Profile


Femtosecond Lasers• Femtosecond lasers have improved flap thickness

reproducibility (VisuMax SD: 8 µm)• We can create thinner flaps (VisuMax: 80 µm)• Thinner flaps extends the range of myopia in LASIK

Pre-release online


Example RST Planning

Refraction -10.75 D sph

Pachymetry 509 µm

Flap Thickness (VisuMax) 80 µm

Ablation Depth 135 µm

Predicted RST 296 µm

Outcomes


New Profile for High Myopia

• 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

• Retreatments– 45% eyes treated as “two-stage”– Enhancement rate (non two-stage): 35%


Advantages of Two Stage Procedure

• 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


Topography Guided Retreatment

Pre Post Reduced

Sph Ab 0.48 µm 0.28 µm 41%

HO RMS 0.72 µm 0.57 µm 21%


MEL80 High Myopia: Accuracy

y = 1.0726x + 0.8394R² = 0.8759

-14

-13

-12

-11

-10

-9

-8

-7-14-13-12-11-10-9-8-7

Attempted vs. Achieved Spherical Equivalent


Achieved Spherical Equivalent (Diopters)


-2.00 To -1.51

-1.50 To -1.01

-1.00 To -0.51

-0.50 To -0.14

-0.13 To

0.13

0.14 To

+0.50

+0.51 To

+1.00

+1.01 To

+1.50

+1.51 To

+2.00

Accuracy 0% 3% 15% 33% 25% 13% 7% 1% 1%

0%3%

15%

33%

25%

13%

7%

1% 1%0%

5%

10%

15%

20%

25%

30%

35%

Percentage Eyes

Accuracy of Spherical Equivalent

Accuracy: Within Range of Intended

MEL80 High Myopia: Accuracy

Within ±0.50 D 71%

Within ±1.00 D 94%


20/12.5 20/16 20/20 20/25 20/32 20/40 20/63

Pre BSCVA 1% 28% 83% 100%Efficacy 11% 47% 90% 97% 99% 99% 99%

1%

28%

83%

100%

11%

47%

90%97% 99% 99% 99%

0%

20%

40%

60%

80%

100%

Percentage Eyes

Monocular UCVA

Efficacy: Monocular UCVA

Monocular Efficacy (excluding eyes not intended plano)

n=176


MEL80 High Myopia: Safety – BSCVA

Loss 3 or More

Loss 2 Loss 1No

ChangeGain 1

Gain 2 or More

Safety 0.0% 0.0% 2% 40% 52% 6%

0.0% 0.0% 2%

40%

52%

6%

0%

20%

40%

60%

Percentage Eyes

Lines Change BSCVA

Safety: Lines Change BSCVA

N=4

n=220


MEL80 High Myopia: Contrast Sensitivity

*

* Statistically significant (p<0.05)


-12.00

-10.00

-8.00

-6.00

-4.00

-2.00

0.00

2.00

Spherical Equivalent (D)

Stability

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

3 Mo 6 Mo 12 Mo 24 Mo


Take Home Message

• 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

Thank You

high myopia final czm dubai_2011

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