Athens-Comparison of Laser In Situ Keratomileusis Flaps Created by 3 Femtosecond Lasers (1)
1. Marija Antičić, Maja Bohač, Mateja Končarević, Alma
Biščević, Sunčana Kovačić, Nikica Gabrić
Specialty Eye Hospital “Svjetlost”
School of Medicine, University of Rijeka
20th ECSRS Winter Meeting Athens
Comparison of Laser In Situ
Keratomileusis Flaps Created by 3
Femtosecond Lasers
DISCLOSURE: None of the authors have a financial interest in any of the products or devices noted
2. FEMTOSECOND LASERS
• The prototype of the first ophtalmic surgical FS laser system
was designed and constructed by Dr Juhasz and his associates
at the University of Michigan College of Engineering Center
for Ultra-fast Optical Scienses (CUOS) in the early 1990s 1
• Have changed refractive surgery in the last 15 years since the
market release of the Intralase Femtosecond laser (Abbot
Medical Optics, Il, USA) in 20011
• The bladeless flap creation rapidly gained popularity because
of its safety, fast recovery and excellent results2
1. Soong HK, Malta JB, Femtosecond lasers in ophtalmology. Am J Ophtalmol 147, 189-197 (2009)
2. Durrie DS, Kezirian GM, Femtosecond laser versus mechanical microkeratome flaps in wavefront-guided laser in situ
keratomileusis: prospective contralatelar study. J Cataract Refractive Surg 31, 120-6 (2005)
3. Why Femtosecond lasers in corneal surgery?
• Ultra-short pulse duration (10-15 sec.) has the ability to deliver
laser energy with minimal collatelar damage to the adjacent
tissue (1μm).
High focus quality
inside the cornea
• Precisely cut corneal flaps
are essential for successful
LASIK.
• Create uniform thickness
planar configuration flaps;
microkeratomes create flaps
with less uniform thickness.
• The creation of a flap of
intended thickness is crutial
for obtaining an appropriate
residual stromal thickness.
4. Mecanism of action: Photodistruption
• FSL energy is absorbed by the
tissue, resulting in plasma
formation.
• The plasma of free electrons and
ionized molecules rapidly
expands creating cavitation
bubbles.
• The force of the cavitation bubble
creation separates the tissue.
• Multiple pulses are applied next
to each other to create a cleavage
plane and ultimately the LASIK
flap.
5. Advantages:
• Reduced incidence of flap complications like buttonholes, free
caps, irregular cuts etc.
• Control over flap diameter and thickness, side cut angle, hinge
position and lenght.
• Increased precision with improved flap safety and better thickness
predictability.
• Capability of cutting thinner flaps to accommodate thin corneas
and high refractive errors.
• Stronger flap adherence.
• The ability to retreat immediately if there is incomplete FS laser
ablation.
• Decreased incidence of epithelial ingrowth and dry eye.
• Better contrast sensitivity
• Less increase in IOP required
6. Disadvantages:
• Opaque bubble layer (OBL)
• Transient light sensitivity syndrome (TLSS)
• Increased difficulty in lifting the flap if retreatment is requred
after that (because of good adherence)
• Increased cost.
7. Femtosecond lasers used in our study:
• Intralase FSTM 150KHZ
(Abbot Medical Optics,
Abbott Park, Illinois)
• Femto LDVTM (Ziemer
Group, Port, Switzerland)
• VisuMax Femtosecond
System® (Carl Zeiss
Meditec, Jena, Germany)
8. Technical Features of Femtosecond Laser Devices for Flap
Creation
Feature Intralase IFS Ziemer LDV Carl Zeiss VisuMax
Puls Rate 150 KHZ 1MHZ 500 KHZ
Pulse duration 500 fs 200 -300 fs 400 (?) fs
Spot size 1-5m 2 m 1 m
Pulse energy 500-1300 nJ 100 nJ 300 nJ
Concept Amplified Oscillator Amplified
Additional feature Greatest number of
treated eyes
Portable, Low energy Flex
Smile
Suction Manual Computer controlled
within handpiece
Computer controlled low
Pressure
Laser-Cornea Coupling Flat Flat Curved
Customizable features High Very limited Very high
9. Purpose
• To compare corneal flap morphology created by the
-Intralase FS (femtosecond group 1)
-Ziemer LDV (femtosecond group 2)
-VisuMax (femtosecond group 3)
• The patients were divided into 3 groups based on the
device used for flap creation.
• Comparative case series, on patients with myopia and
myopic astigmatism who were consecutively
scheduled for bilateral LASIK treatment –from
February 2013 to July 2015.
10. Mean ± SD
Group 1 Group 2 Group 3
Characteristic Intralase IFS Ziemer LDV VisuMax
No. eyes 82 82 82
Mean age, yr 25.0±5.1 26±5.7 26±5.5
Mean SE, D -6.4±2.2 -6.7±2.8 -6.5±2.5
Mean CCT, μm 560±25,6 564±28.9 559±27,3
Mean corneal
curvature, D
44±1.8 43.5±1.4 43.8±1.7
CCT, central corneal thickness; SE, spherical equivalent refraction
PREOPERATIVE DEMOGRAPHICS
11. We evaluated:
• Central flap thickness
• Mean flap thickness
• Meridian flap uniformity
• Difference between the mean central and mid-peripheral
flap thickness 2 mm in the horisontal and vertical plane
• Flap thickness predictability (mean deviation between the
achieved and attempted flap thickness)
• OCT (Carl Zeiss Meditec AG, Jena Germany) for
assessing flap regularity, uniformity and predictability
• Flap thickness was determined at 10 points, 3 months
postoperatively
• Intented flap thickness was 110 μm
15. Matherials and Methods
• Measurements of the flaps in the 0-, and 90- degree lines
0o
45o
90o
135o
180o
225o
270o
315o
16. Statistical analyses were performed using
statistical software MedCalc for Windows,
version 11.5.1.0 (MedCalc Software,
Mariakerke, Belgium)
17. Results
Central and Mean Flap Thickness
Central mean SD
1. Ziemer LDV 94,04 3,20
2. VisuMax 105,58 15,55
3. Intralase IFS 111,0 11,50
Kruskal Wallis test: P<0.001, post hoc test (p<0,05, 1 vs. 2 and 3, 2 vs 1, 3 vs 1)
Mean flap mean SD
1. ZiemerLDV 110,78 11,29
2. VisuMax 105,68 16,5
3. Intralase IFS 107,44 10,76
Kruskal Wallis test: P<0.001, post hoc test (p<0,05, 1 vs. 2 and 3, 2 vs 1, 3 vs 1)
18. ZIEMER LDV (mean +/- SD )
Kruskal Wallis test P<0,001
Flaps in femtosecond laser Ziemer LDV had the assymerty between the center and periphery.
These findings are consistent with other authors. 3
3. Hyunseok Ahn, MD, Jin-Kook Kim et al. Comparison of laser in situ keratomileusis flaps created by 3 femtosecond lasers and a microkeratome. J
Cataract Refract Surg; 37:349–357 (2011).
19. VisuMax (mean +/- SD )
Kruskal Wallis test P= 0,609
The disparity between center and periphery flap thickness was not statistically significant.
20. Intralase IFS (mean +/- SD )
Kruskal Wallis test P= 0,323
The disparity between center and periphery flap thickness was not statistically significant.
21. Meridian flap uniformity
Mean(SD)
90 degrees 180 degrees P
1. ZiemerLDV 110,73 (11,31) 110,83 (11,30) 0,981
2. VisuMax 107,46 (16,67) 103,9 (16,41) 0,365
3. Intralase IFS 108,50 (11,05) 106,38 (11,42) 0,596
Meridian flap uniformity measured at the 10 measurement points at 90- and 180-
degrees were uniform and regular for each femtosecond device.
22. The mean center vs. mid-periphery 2 mm in the horisontal and vertical plane
Central SD cent Mid perif SD perif P
1. ZiemerLDV 94,048 3,20 108,27 4,63 <0,001
2. VisuMax 105,58 15,55 108,125 17,09 0,667
3. Intralase IFS 111,00 11,5 106,36 10,37 0,103
Mann Whitney U test
0o
90o
24. Results
Flap thickness Accuracy
(the mean deviation between the achieved and attempted flap
thickness)
Percentage %
Percentage (%)
μm <5 5-10 >10 P
1. ZiemerLDV 39 30 31 0,417
2. VisuMax 40 36,7 23,3 0,496
3. Intralase IFS 40,8 30,9 27,3 0,385
25. Conclusions
• Although the central flap thickness created by the
Ziemer LDV was less than that created by the Intralase
and VisuMax, measurements of 3 femtosecond lasers
were close to the intended thickness.
• The Femto-LDV system was the most predictable in
terms of flap creation (intended versus measured flap
thickness).
• Flaps in the Visumax group had the least difference
between the mean peripheral and the central flap
thickness.
• Flap morphology differed according to the system used.
Usporedba debljine flapova kreiranih sa 3 različita femtosecond lasera.
Femtosecond lasers have changed refractive surgery in the last 15 years since the market release of the Intralase Femtosecond Laser (Abbott Medical Optics, IL, USA) in 2001.
The bladeless flap creation rapidly gained popularity because of its promised increased safety, fast recovery and excellent results
Use a near infrared femtosecond laser with a wavelength of approximately 1053 nm that uses ultrafast pulses with a duration of 100 fs.
The higher laser frequency permits lower energy per pulse and tighter line separation
There is an inverse relationship between the laser pulse duration and the energy required in each pulse to generate the optical breakdown.[3] A shorter pulse (200-500 fs) needs lower energy to achieve the threshold of photodisruption than a longer pulse (500-1300 fs). After the optical breakdown occurs, plasma is created and a cavitation bubble formed. This bubble expands and cleaves the tissue. If a high-energy photodisruption is used, the bubble is larger and the pulses do not need to be placed close together. Low-energy systems create a very small bubble, with a greater number of pulses in an overlapping pattern being mandatory, since there is almost no tissue cleaving induced by the bubbles.
The formation of a bubble layer occurs along the cutting plane, which in some cases leads to an escape of some bubbles into deeper stroma with the formation of an OBL. These deeper bubbles may take a few hours to disappear, and if severe, may impair the aim of the eye tracker during surgery. This is less common with a softer docking (applanation) pressure, lower energy and faster repetition rate devices.[17]. Less opaque bubble layer (OBL) formation is expected owing to a new laser profile that creates specific cutting geometries (externalized channels) in the cornea to allow the gas bubbles to diffuse out of the relevant regions of the cornea. Transient light-sensitivity syndrome is characterized by photophobia and mild pain that can appear days after surgery and can persist for weeks
The main commercially available femtosecond devices have different concepts and applications on how the technology should be used. The IntraLase was the first device and set the standards regarding energy delivered and geometry of cuts. It has raster pulsse pattern: - pulses are applied in a linear pattern, starting at the hinge area, passing through center of the cornea and exytending to the opposite edge.The method for fixating the eye (suction ring and docking system):flat applanation docking system. Laser pulse rate 150 KH-allowing faster procedures. Increase in side cut angle (>90°, allowing inverted bevel-in edge)
Increased geometry of cuts (allowing intrastromal corneal ring placement and shaped corneal transplants). The LDV from Ziemer is a device entirely focused on flap creation with very high pulse rate (in the MHz range) with very low pulse energy (in the nanojoules range)- produces a smoother bed with less bubble formation.There are no vertical side cuts: flap-making approach is similar to a microkeratome with a tapered flap edge. Limitations:procedure is not directly visible during the application of pulses, there is a need for an interface fluid (viscoelastic substance). VISUMAX: spiral pulsse pattern:-laser pulses began centrally and expand centrifugally out to the periphery. Curved applanation docking system, which promises less intraocular pressure (IOP) increase in a more physiologic interface between the eye and the laser. Limbal suction mechanism compared with the standard conjunctival suction.500-KHz pulse rate to be used together with a lower pulse energy profile, in the submicrojoule range.
The current IntraLase FS system use higher-energy, lower-frequency pulses than the Femto LDV laser. The VisuMax falls somewhere in the middle.
Flap creation for LASIK was performed using an Intralase (femtosecond group 1), Ziemer LDV (femtosecond group 2) or Visumax (femtosecond group 3).
femtosecond laser assessing uniformity, accuracy and predictability of flap creation.
No significant differences were observed between 3 femtosecond laser groups
OCT-optical coherence tomography was used for assessing flap regularity, uniformity, accuracy and predictability
.
Centralno je flap tanji kod Ziemer LDV-a jer je to posljedica mehaničkog skeniranja pri čemu fokus u centru i na periferiji se razlikuje za iznos greške.
The Ziemer LDV group had the greatest difference in central and peripheral thickness which is similar result with
