H. Lubatschowski T. Ripken, U. Oberheide, C. Ziltz, G. Gerten Femtosecond Laser Applications in the Huaman Lens
fs-laser induced elasticity changes to improve presbyopic lens accommodation presbyopia material & methods lens cutting precision deformation ability
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
Treatment conception overcome lens-hardening regain lens elasticity smooth µm cuts inside the crystalline lens fs laser pulse 1 mm lens tissue fs LASIK
Treatment conception Ray Myers and Ron Krueger first reported on the concept of laser modification of the crystalline lens in 1998. First experimental results 2001 by Krueger et.al. with ns-pulses 2.5 to 7 mj pulse energy increased elasticity of 11 lens pairs too large residual bubbles (increase of volume / light scattering) Accomodative Potential after Nd:YAG Laser Photodisruption, Ophthalmology 2001
Cutting effect: Photodisruption focussed fs laser beam nonlinear absorption plasma 1-5 µm shock wave cavitation bubble gas bubble
Laser induced cavitation and bubble formation in water Laser Pulse E puls ~ 4µJ τ puls ~ 160fs
Ultrashort pulse lasersystem Bright System Thales diode-pumped Nd:YLF IMRA fs-oscillator Ti:Sa-regen and doublepass 150 fs 5 khz 1.5 W 780 nm
Scanner & 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 suction unit
Influence of laser parameters 2 µj 4 µj frontal cut 5 µm 7 µm 9 µm
Testing simple geometric patterns inside the lens annular combined star-like or steering-wheel pattern cylindric parameter: number of rings cutting width cutting depth spot separation pulse energy samples: ex vivo pig-eyes immediatly enucleated treatment within 6 hours
Steering wheel pattern arbritrary height inner and outer diameter number of planes spot separation pulse star-like, energy annular 680 nj and repetition cylindricalrate cut5 khz pulse in a pig duration lens 150 fs spot pulse separation energy about 5 µm 830 nj
Optimizing the cutting precision Decrease of pulse energy from 1 µj down to 400 nj Cutting of 'sagittal' patterns with an off-axis angle (conical cuts) off-axis angle
Optimizing the precision: off-axis angle cylindrical cut off-axis angle 0 conical cut off-axis angle 30 conical cut off-axis angle 45 decreasing of bubble size PAA sample pulse energy: 1.4 µj spot separation: x und z = 5 µm
Optimizing the precision: off-axis angle Pig lens histological section 45 off-axis angle 30 off-axis angle cylindrical cut less bubbles pulse energy 0.52 µj spot separation x and z = 5 µm
Optimizing the cutting precision Decrease of pulse energy from 1 µj to 400 nj Cutting of sagittal patterns with an off-axis angle Increasing of spot separation in sagittal cuts
Optimizing the precision: spot separation less bubbles 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
Lens deformation ability changes - setup CCD-camera rotation stage a) 0 rpm b) 1035 rpm c) 1850 rpm
Lens deformation ability changes Comparison of treated and untreated pig lenses average of 60 lenses one pig lens higher deformation ability 20% increase of ability of lens deformation
Fs-laser induced elasticity changes to improve presbyopic lens accommodation Summary 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 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
Holger Lubatschowski hl@lzh.de www.lzh.de