Overview of Commercially Available Femtosecond Lasers in

Refractive Surgery

Holger Lubatschowski

The author receives research funds fromZiemer Ophthalmic Systems Group

Commercially Available Femtosecond Lasers in Refractive Surgery

VisuMax ®Zeiss

FS laserINTRALASE®

available information

FEMTEC ®

20/10 Perfect VisionFEMTO LDV®

Ziemer

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

Photodisruption, Optical Breakdown

focussed fs laser beam

nonlinear absorption

plasma

shock wave

cavitation bubble

gas bubble

Laser induced Cavitation and Bubble Formation in Water

Laser Pulse

Epuls ~ 4µJ

τpuls ~ 160fs

• 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

Factors that minimize Engery Threshold for

Photodisruption

• Pulse Duration

5

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

Factors that minimize Engery Threshold for

Photodisruption

• Pulse Duration

• Numerical Aperture

Numerical Aperture

The larger the NA,

the smaller the focal spot volume,

the smaller the energy threshold

Two ways to increase NA

w1

• increasing lens diameter

2

2

f

w=

1

1

f

w=NA

INTRALASE® FS laser

Two ways to increase NA

w1

• increasing lens diameter

2

2

f

w=

1

1

f

w=NA

• decreasing focal length

f1

f2

w2

Two ways to increase NA

w1

• increasing lens diameter

2

2

f

w=

1

1

f

w=NA

• decreasing focal length

f1

f2

w2

Two Different Concepts in Photodisruption Process

"High" Pulse Energy (µJ) "Low" Pulse Frequency (kHz)

(nJ) "Low" Pulse Energy(MHz) "High" Pulse Frequency

?

Two Different Concepts in Photodisruption Process

"High" Pulse Energy (µJ) "Low" Pulse Frequency (kHz)

(nJ) "Low" Pulse Energy(MHz) "High" Pulse Frequency

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)

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

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

Surface Quality

Mikro Keratome DaVinciIntralase

VisuMax Femtec

Surface Quality

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

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)

Special Features during Operation

DaVinci:

Fits under all Excimer Lasers

• no movement of the patient necessary

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:

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):

H.Lubatschowski@LZH.de

www.biophotonics.uni-hannover.de