Femtosecond Laser-Induced Retina Damage Thresholds in Pig Eyes - UNMC
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6/7/2021
Femtosecond Laser-Induced Retina
Damage Thresholds in Pig Eyes
LAKE LARSON
OPTICAL ENGINEER
EXTREME LIGHT LABORATORY
UNIVERSITY OF NEBRASKA-LINCOLN
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Outline
1. Vitreoretinal Surgery and Limitations
2. Introduction to Laser-Surgical Applications
3. Femtosecond Laser Experimentation in Posterior Segment
4. Future Directions
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Invasive Vitreoretinal Surgery Practices
Today, the only surgical practice for the retina is invasive.
Number done a year: ~300,000
Possible Morbidities
• Cataract Formation
• Glaucoma
• Infection
• Haemorrhage
• Vision Loss/Loss of Eye
Developing non invasive approaches would
improve outcomes.
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Current Noninvasive Laser Surgical Practices
Lasers are a promising approach to improve outcomes.
Commonly used to treat anterior segment disease.
but reaching the posterior segment requires passing through the vitreous
without causing damage while maintaining the integrity of the laser pulse.
Nanosecond lasers (SI unit: 10-9 seconds)
Most commonly used for floater treatment.
Limitations of Current Technology:
• Cannot be performed within 2mm of eye surfaces
• 20% of the eye is inoperable
• The retina is unreachable
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Femtosecond Laser Introduction
Femtosecond (SI unit: 10-15 seconds)
Able to operate microns from the retina while minimizing collateral damage.
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Cavitation
Tissue cutting done by ionization.
Using femtosecond lasers, we must reach the
retina while preserving:
• Focal spot quality
• Energy density
• High cutting precision
• Repeatability
This will allow us to make micron sized cuts to the
retina while minimizing collateral damage to the
underlying and surrounding tissue.
The goal is to make cuts to the retina as shown
in the last slide.
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Experimentation
How Can this be Done? 1. Through Vitreous
Using:
• Femtosecond Lasers
• Temporal Dispersion Control 2. At the Retina
• Vitreous Cavitation
precise micron, retinal cutting.
3. Above the Retina
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Parameters of Experiments
Femtosecond Laser (Archimedes Laser)
• Ti:Saph, Broadband Laser System
• 10 micron focal-spot diameter
• ~28 femtoseconds
• 800nm central wavelength
• 100nm total bandwidth
• Rep Rate: 10Hz
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Experiment 1 No Compensation
Compressed Uncompressed
Vitreous Compensation
Traveling through media such Dispersive
Media
as vitreous adds dispersion;
which decreases pulse
duration and therefore pulse V(red) > V(blue)
intensity.
Pre Compensation
Compensated Compressed
Pulse Morphology must be
preserved through the vitreous. Dispersive
Pre-Compensation (negative Media
dispersion) does this.
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Experiment 1 38 fs
AIR
Determining Dispersion
Through Vitreous.
Laser pulses were sent
through various situations to
VITREOUS
80 fs
determine the negative
dispersion required to deliver
a compressed pulse through
the vitreous to the retina.
COMPENSATED
FROG system used to 38 fs
measure temporal
parameters of the pulse.
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Experiment 2
Determining Damage Threshold
Determining an energy-per-pulse
that is able to cause retinal
cavitation while not damaging
underlying structures is essential for
this practice.
Using multiple pulse
energies, we can
determine a threshold
for retinal surface
damage.
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Experiment 2
Determination of Cavitation
Threshold. 2
(um ±SD) ENERGY
Pulses were focused on the 2,346.7 ± 378.8 (n=4) 12 nJ
retina
4,968.1 ± 347.1 (n=2) 115 nJ
Four energy levels were used 15,220.4 ± 6974.3 (n=5) 12 uJ
7,174.1 ± 2388.9 (n=5) 21 uJ
Burn area on the retina was
determined via SEM analysis F(3,12) = 7.52
p = 0.0043
A damage threshold of
6.4 mJ/cm2 was determined
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Experiment 3
Gaussian Laser Focus
Cavitation above the Retina
We can make predictions
Propagation
about retinal cavitation as a
function of distance.
This will give us a safe range for
vitreoretinal surgery and how
far away cuts can be made
from the retinal surface.
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Experiment 3
Distance to Damage Curve
One energy level, 20nJ/pulse
The focus (cavitation location)
was scanned away from the
retina
Expectation is a falloff of
damage, and then a clear cut
off.
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Retinal Surface Topography
Z-Axis Scan
For three, shots; the depth was calculated to be
~200um deep from the surface of the retina.
Used for depth and diameter of retinal damage.
We look forward to having these results soon.
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Summarization of Experiments
EXPERIMENT 1 EXPERIMENT 2 EXPERIMENT 3
Negative dispersion was A cavitation threshold was Pulses were scanned
used to compensate for determined using multiple away from the retinal
effects as the laser pulses pulse energies to ablate surface at the determined
pass through the vitreous. the retinal surface directly. cavitation threshold to find
a damage-to-distance
curve.
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Future Directions
OCT (Optical Coherence Tomography) Adaptive Optics System
OCT will be used to determine both depth of Aberration introduced from structures of the
cuts performed by cavitation, and the retinal eye and optical components will be
layers affected. corrected using a closed-loop, wavefront
sensor and deformable mirror system.
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References
Ben-Yakar, A., & Byer, R. L. (2004). Femtosecond laser ablation properties of borosilicate glass. Journal of Applied Physics, 96(9),
5316–5323. doi:10.1063/1.1787145
Retinal Detachment. Better Health Channel. (2017, July 27).
https://www.betterhealth.vic.gov.au/health/ConditionsAndTreatments/retinal-detachment#bhc-content.
Acknowledgements
Dr. David E. Anderson - Department of Ophthalmology and Visual Science, UNMC
Junzhi Wang - Department of Physics and Astronomy, UNL
Dr. Ronald Krueger - Department of Ophthalmology and Visual Science, UNMC
Dr. Renfeng Xu - Department of Ophthalmology and Visual Science, UNMC
Dr. You Zhou - Department of Biology, UNL
Dr. Geunyoung Yoon - Department of Ophthalmology, University of Rochester Medical Center
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Supplementary
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Adaptive Optics
Incoming, distorted
wavefronts are measured
using a Wavefront Sensor
such as a Hartmann Shack.
The wavefronts are then
corrected by a deformable
mirror.
This closed loop system allows
for minimal aberration in
pulse morphology.
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Adaptive Optics in
the Eye
175
um
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Simplified Experimental Setup
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