H. LubatschowskiT. Ripken, U. Oberheide, C. Ziltz, G. Gerten

Femtosecond Laser Applicationsin the Huaman Lens

presbyopia

material & methods

lens cutting precision

deformation ability

fs-laser induced elasticity changes to improve presbyopic lens accommodation

Presbyopia - preconditions

Helmholtz theory accommodation failure because of:

• loss of lens elasticity

• tissue hardening inside the lens

however:• ciliary muscle

stays activ• lens capsule

stays elastic

• overcome lens-hardening• regain lens elasticity

Treatment conception

smooth µm cuts inside thecrystalline lens

fs LASIK

1 mm1 mmlens tissue

fs laserpulse

Ray Myers and Ron Krueger first reported on the concept of laser modification of the crystalline lens in 1998.

Treatment conception

First experimental results 2001 by Krueger et.al. with ns-pulses

Accomodative Potential after Nd:YAG Laser Photodisruption, Ophthalmology 2001

• 2.5 to 7 mJ pulse energy

• increased elasticity of 11 lens pairs

• too large residual bubbles (increaseof volume / light scattering)

Cutting effect: Photodisruption

1-5 µm

focussed fs laser beam

nonlinear absorption

plasma

shock wave

cavitation bubble

gas bubble

Laser induced cavitation and bubble formation in water

Laser PulseEpuls ~ 4µJτpuls ~ 160fs

Bright System Thales

Ultrashort pulse lasersystem

diode-pumped Nd:YLFIMRA fs-oscillatorTi:Sa-regen and doublepass

150 fs l 5 kHz l 1.5 W l 780 nm

Scanner & Suction Unit

suction unit

• scanner positions in x-y-plane • eye-fixation with lightly depressure• suction unit translates in z-direction• f-theta-optic• accuracy approx. 1 µm• focal spot approx. 5 µm

Influence of laser parameters

2 µJ 4 µJ

5 µm

7 µm

9 µm

frontal cut

parameter:• number of rings• cutting width• cutting depth• spot separation• pulse energy

samples: ex vivo pig-eyes

immediatly enucleatedtreatment within 6 hours

Testing simple geometric patterns inside the lens

cylindricstar-likeannular combined orsteering-wheel

pattern

pulse energy 680 nJrepetition rate 5 kHzpulse duration 150 fsspot separation 5 µm

star-like, annular and cylindrical cutin a pig lenspulse energy about 830 nJ

Steering wheel pattern

arbritrary• height• inner and outer diameter• number of planes• spot separation

off-axis angle

• Decrease of pulse energy from 1 µJ down to 400 nJ

• Cutting of 'sagittal' patterns with an off-axis angle (conical cuts)

Optimizing the cutting precision

PAA samplepulse energy: 1.4 µJspot separation: ∆x und ∆z = 5 µm

cylindrical cutoff-axis angle 0°

conical cutoff-axis angle 30°

conical cutoff-axis angle 45°

decreasing of bubble size

Optimizing the precision: off-axis angle

pulse energy 0.52 µJ

spot separation ∆x and ∆z = 5 µm

less

bubble

s

cylindrical cut

30° off-axis angle

45° off-a

xisangle

Pig lens histological section

Optimizing the precision: off-axis angle

• Decrease of pulse energy from 1 µJ to 400 nJ

• Increasing of spot separation in sagittal cuts

• Cutting of „sagittal“ patterns with an off-axis angle

Optimizing the cutting precision

pulse energy: 1.4 µJ

spot separation: ∆x = 5 µm

a) ∆z = 5 µm

b) ∆z = 10 µm

c) ∆z = 20 µm

d) ∆z = 40 µm

PAA sample

less

bubble

sOptimizing the precision: spot separation

a) 0 rpm

Lens deformation ability changes - setup

rotation stage

CCD-camera

c) 1850 rpmb) 1035 rpm

Comparison of treated and untreated pig lenses

Lens deformation ability changes

hig

her

def

orm

atio

nab

ility

average of 60 lensesone pig lens

20% increase of ability of lens deformation

• NIR-fs-photodisruption enables 3D-cuts inside the lens

• easy procedure, no visual side-effects appear (ex vivo)

• improvement in frontal cuts

• microcuts increase lens deformation ability

Summary

Outlook• need of measuring the regain of elasticity in prespyobic lenses

• optimization of cutting patterns with respect to an elasticity maximum

• further investigations on lens biomechanics

• in vivo studies

Fs-laser induced elasticity changes to improve presbyopic lens accommodation

Holger Lubatschowskihl@lzh.de www.lzh.de