overview of commercially available femtosecond lasers in … · 2017. 10. 21. · ]/[ ttti...
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Overview of Commercially Available Femtosecond Lasers in
Refractive Surgery
Holger Lubatschowski
The author receives research funds fromZiemer Ophthalmic Systems Group
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Commercially Available Femtosecond Lasers in Refractive Surgery
VisuMax ®Zeiss
FS laserINTRALASE®
available information
FEMTEC ®
20/10 Perfect VisionFEMTO LDV®
Ziemer
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Intensität [W/cm²]
photo-disruption
vaporisation
photo-ablation
coagulation
100 J/cm²
10 J/cm²
1 J/cm²
0,1 J/cm²
photo chemistry
10 10 10 1010 -910 -12 -6 -3
Interation time [s]
0 3
10
10
10
10
10
-310
0
3
6
9
12
Inte
ns
ity
[W/c
m2]
Laser Tissue Interaction
linear absorption
non-linear Absorption
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Photodisruption, Optical Breakdown
focussed fs laser beam
nonlinear absorption
plasma
shock wave
cavitation bubble
gas bubble
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Laser induced Cavitation and Bubble Formation in Water
Laser Pulse
Epuls ~ 4µJ
τpuls ~ 160fs
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• Threshold for disruption scales with pulse intensity
many, many photons on the same place, at the same time
• Unwanted side effects (bubbles, collateral damage) scales with pulse energy
photon energy is converted into heat, kinetics, chemistry
Threshold for disruption
Beam Diameter
Inte
ns
ity
Pulse Width
Pulse Energy
Preconditions of Photodisruption for precise Corneal Surgery
Pulse Energy
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Factors that minimize Engery Threshold for
Photodisruption
• Pulse Duration
5
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own measurements
num. simulation (Noack et al.)
Flu
en
ce
[J/c
m2]
0,01 0,1 1 10 100 1000 10000 100000 1000000
0,1
1
10
100
1000
10000
0,1
1
10
100
1000
10000
Inte
ns
ity
[10
11
W/c
m2]
Puls Duration [ps]
Threshold for Optical Breakdownas a function of Pulse Duration
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Factors that minimize Engery Threshold for
Photodisruption
• Pulse Duration
• Numerical Aperture
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Numerical Aperture
The larger the NA,
the smaller the focal spot volume,
the smaller the energy threshold
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Two ways to increase NA
w1
• increasing lens diameter
2
2
f
w=
1
1
f
w=NA
INTRALASE® FS laser
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Two ways to increase NA
w1
• increasing lens diameter
2
2
f
w=
1
1
f
w=NA
• decreasing focal length
f1
f2
w2
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Two ways to increase NA
w1
• increasing lens diameter
2
2
f
w=
1
1
f
w=NA
• decreasing focal length
f1
f2
w2
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Two Different Concepts in Photodisruption Process
"High" Pulse Energy (µJ) "Low" Pulse Frequency (kHz)
(nJ) "Low" Pulse Energy(MHz) "High" Pulse Frequency
?
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Two Different Concepts in Photodisruption Process
"High" Pulse Energy (µJ) "Low" Pulse Frequency (kHz)
(nJ) "Low" Pulse Energy(MHz) "High" Pulse Frequency
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Two Different Concepts in Photodisruption Process
Spot Size
Spot Separation
Spot Size
Spot Separation
cutting process driven by mechanical
forces (expanding bubbles)
cutting process limited by focal spot size
(many pulses needed)
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40 µm
Pulse Energy: 30 nJ
Pulse Width: 250 fs
Pulse Energy: 2 µJ
Pulse Width: 930 fs
100 µm100 µm
Two Different Concepts in Photodisruption Process
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Pulse Energy: 2 µJ
Pulse Width: 930 fs
100 µm100 µm
Two Different Concepts in Photodisruption Process
100 µm
Pulse Energy: > 30 nJ
Pulse Width: 250 fs
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Surface Quality
Mikro Keratome DaVinciIntralase
VisuMax Femtec
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Surface Quality
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Special Features during Operation
© Intralase
Intralase, Femtec, VisuMax:
Cutting process is visible during operation
DaVinci:
Operates like a mechanical Knife,
no direct view on cutting process(AMADEUS technology)
© DaVinci
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Special Features during Operation
Femtec, VisuMax:
Spherical contact interface to cornea• Minimal applanation & IOP increase
© 20/10 PV
VisuMax:
Corneal fixation of the contact glass• assures a better fixation than scleral fixation
FS Lenticule Extraction (FLEX)
• "All fs-LASIK" (10 eyes)
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Special Features during Operation
DaVinci:
Fits under all Excimer Lasers
• no movement of the patient necessary
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Comparison (tech. features)
some MHzsome 100 kHzsome 10 kHz60 kHzRep Rate:
some nJ< 1 µJ> 1 µJ≈ 1 µJPulse Energy:
< 1 µm≈ 1 µm (?)> 1 µm> 1 µmSpot Size:
≈ 250 fs≈ 400 fs (?)> 500 fs> 500 fsPulse Width:
≈ 1040 nm≈ 1040 nm≈ 1040 nm≈1040 nmWavelength:
OscillatorAmplifier (?)AmplifierAmplifierConcept:
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Comparison (handling)
industr laser head(?)const. temp/
humidity
const. temp/
humidity
requirements to
environm.:
> 400 eyes≈ 20 eyes(?)1 Mio eyesClinical exp.;
very small,
mobile very bulky,fixedbulky, fixedbulky, fixedSize, mobility:
limitedvery high (?)highvery highCutting geom. / flexibility:
comparable to
microtome
comparable to
microtome
comparable to
microtome
comparable to
microtomeSurface quality:
< 40 sec< 40 sec (??)1 min (?)< 30 secOperation speed(@ 9,5 mm):