Intraocular Photodisruption With Picosecond and Nanosecond Laser

Tissue Effects of Picosecond and Nanosecond Photodisruption 3043
however, the same for ns pulses so that the use of ps
pulses remains as advantageous in the periphery as it
does close to the optical axis.
Although an automatic scanning and aiming system
operating at high repetition rates would be useful
for phacofragmentation or corneal refractive surgery,
manual aiming seems to be most appropriate for vitreoretinal
laser applications. With manual aiming
controlled by the direct feedback from observing the
action of the laser pulses, the highest possible surgical
precision can be realized, together with a minimization
of the light energy deposited. To keep the total
amount of light energy applied as low as possible, only
moderate repetition rates of 10 to 100 Hz should be
used. Light absorption in the retinal pigment epithelium
might otherwise lead to heating and coagulation
of the retina, in addition to possible mechanical damage
associated with misaimed laser pulses.
CONCLUSIONS
The use of ps pulses with a moderate repetition rate
(10 Hz to 1 kHz) and energies in the microjoule range
is a new concept compared to the well-established
Nd:YAG laser surgery with single ns pulses. It increases
the surgical precision and reduces the disruptive
side effects in "classical" Nd:YAG laser applications
like posterior capsulotomy and iridotomy and in
the whole range of other applications for which treatment
with ns pulses is already well established. Besides
that, it also renders new applications possible. Our
preliminary investigations suggest that cataract emulsification,
vitreoretinal surgery close to the retina, and
intrastromal corneal refractive surgery deserve further
in vivo experiments and clinical studies. An instrument
with a repetition rate variable between 10 Hz
and about 1 kHz, offering the possibility of manual
aiming and automatic scanning, would be most versatile.
Pulse energies below 1 mj will be sufficient in
most cases, but for cataract fragmentation the range
of pulse energies available should reach up to about 2
to 3 mj to allow fragmentation of dense cataracts.
Key Words
Nd:YAG laser, picosecond pulses, refractive surgery, cataract
fragmentation, vitreoretinal surgery
Acknowledgments
The authors thank M. Volkholz, C. Grosse, and U. Weinhardt
for their support during the histologic investigations,
and L. Merz, H. Krohn, R. Kube, and R. Carbe for their help
in preparing the manuscript.
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