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Commercial Disclosures
- Jerome C. Ramos-Esteban, MD (none)
- Ronald R. Krueger, MD (IntraLase)
- Maria Regina Chalita, MD, PhD (none)
- Daniel Pierre, MSIV (none)
Corneal Changes Following LASIK and Enhancement with Microkeratome - - PowerPoint PPT Presentation
Corneal Changes Following LASIK and Enhancement with Microkeratome - - PowerPoint PPT Presentation
Corneal Changes Following LASIK and Enhancement with Microkeratome and Femtosecond Laser Flaps Jerome C. Ramos-Esteban, MD Cole Eye Institute Cleveland Clinic Commercial Disclosures Jerome C. Ramos-Esteban, MD (none) Ronald R.
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Purpose
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Purpose
- To determine the thickness of both LASIK flaps and
residual stromal bed at the time of primary LASIK and LASIK enhancement
- To compare differences in these two parameters
according to ablation type
- To determine longitudinal changes in these two
parameters between Microkeratome and femtosecond laser procedures
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Methods
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98 patients n=196 eyes Microkeratome n=79 eyes Femtosecond N=117 eyes Primary LASIK treatment Myopia n=91 Hyperopia=26 Myopia n=59 Hyperopia=20
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Methods
Primary procedures:
- Microkeratome (Moria M2, 110 um head)
- Femtosecond (IntraLase 15 and 30 kHz, 110 um flap)
Laser Platform:
- Alcon LadarWave 4000
- Preoperative and intraoperative Ultrasound Pachymetry
50 HZ (Sonogage) probe
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Measurements
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Measurements
Primary Procedures
- Central Corneal Thickness
- Pre-ablation Stromal Thickness
- Post-ablation Stromal Thickness
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Measurements
Enhancement Procedures
- Central Corneal Thickness
- Pre-enhancement Stromal Thickness
- Post-ablation Stromal Thickness
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Calculations
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Primary Procedures
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Central Corneal Thickness (CCT)
(CCT)
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Primary Flap Thickness (PFT)
PFT = CCT - PAST
Preablation Stromal Thickness (PAST)
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Calculated Primary Post-Ablation Depth (CPPAD)
CPPAD = PAST - TLAD
Theoretical Laser Ablation Depth (TLAD)
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Measured Ablation Depth (MAD)
MAD = PAST - POST
Post-Ablation Stromal Thickness (POST)
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LASIK Enhancements
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Enhancement Central Corneal Thickness (ECCT)
(ECCT)
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Enhancement Flap Thickness (EFT)
EFT = ECCT - PEST
Pre-enhancement Stromal Thickness (PEST)
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Calculated Enhancement Post-Ablation Depth (CEPAD)
CEPAD = PEST - TLAD
Theoretical Laser Ablation Depth (TLAD)
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Measured Enhancement Ablation Depth (MEAD)
MEAD = PEST - POST
Post-Ablation Stromal Thickness (POST)
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Statistical Analysis
- Paired t-test was used to assess differences in
thickness between:
- Primary & Enhancement flaps
- Calculated & pre-enhacement stromal thickness
- Calculated & Measured ablation depth
- A p value < 0.05 was considered statistically significant
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Results
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Microkeratome
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Microkeratome Flap Thickness
0.94 119.8 120 Hyperopia <0.0001 141.8 114.9 Myopia p value EFP PFT Mean
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Microkeratome
Residual Stromal Bed Thickness
<0.0001 411.5 366 Hyperopia <0.0001 346.6 364.1 Myopia p value PEST CPPAD Mean
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Femtosecond
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Femtosecond: Flap Thickness
0.07 118.6 126 Hyperopia 0.003 141 134.9 Myopia p value EFT PFT Mean
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Femtosecond:
Residual Stromal Bed Thickness
<0.0001 421.2 376.32 Hyperopia <0.0001 331.8 351.2 Myopia p value PEST CPPAD Mean
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Femtosecond Primary Treatment Difference in Ablation Depth
<0.001 19 54 Hyperopia <0.001 102 85 Myopia p value MAD TLAD Mean
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Femtosecond Enhancement Difference in Ablation Depth
<0.001 7 21 Hyperopia <0.001 10 15 Myopia p value MEAD ETLAD Mean
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Primary LASIK vs. Enhancements
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Flap Thickness Difference Primary LASIK vs. Enhancement
0.07
- 7.42
0.94
- 0.25
Hyperopia
0.003 + 6.1 <0.001 + 26.3 Myopia
p value Femtosecond p value Microkeratome
FT = EFT - PFT
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Stromal Thickness Difference Primary LASIK vs. Enhancement
<0.001 + 44.8 <0.001 + 45.6 Hyperopia <0.001
- 19.4
<0.001
- 17.97
Myopia
p value Femtosecond p value Microkeratome
ST = PEST - CPPAD
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Conclusions
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Microkeratome vs. Femtosecond
Myopic Ablations
- PFT thinner due to underestimation of pre-ablation stromal bed
- Calculated post ablation depth > pre-enhancement stromal bed
- Substraction methods are very sensitive to tissue hydration
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Microkeratome vs. Femtosecond
Myopic Ablations
- PFT femtosecond flaps > microkeratome flaps
- Possible fluid displacement during flap creation
- Difference Femtosecond & microkeratome EFT not significant
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Microkeratome vs. Femtosecond
Hyperopic Ablations
- No statistically significant differences between PFT and EFT
- Pre-enhancement stromal bed > calculated post ablation depth
- Lamellar tension reduction from more peripheral ablation
may lead to increased baseline tissue hydration
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