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Laser Systems& Benefits
Excimer lasers, designed for
laser-assisted in situ
keratomileusis (LASIK), are
marvels of modern medicine.
Although all approved
excimer lasers meet safety
and effectiveness criteria
established by the U.S FDA,
certain people may be better
off with one type of laser
over another.
Types of Modern Excimer
Lasers Used for LASIK
Slit scanning lasers
- Slit scanning lasers use
relatively small beams
linked to a rotational
device with slit holes that
enlarge. The laser beams
scan across these holes
during surgery, producing a
gradually enlarging ablation
zone. The approach provides
a uniform beam and -
potentially - smoother
ablations than obsolete
broad-beam lasers. The
disadvantages include a
slightly greater risk of
decentration and
overcorrection unless an
eye-tracker is being used
with the laser.
Spot scanning lasers
- Spot scanning (or
"flying-spot") lasers, which
are the most common, use
small-diameter laser beams
(0.8 to 2 mm) scanned across
the cornea to produce the
ablation zone. This approach
has the potential to produce
the smoothest ablations, to
more readily allow
customized ablations and to
better treat irregular
astigmatism.
Wavefront-guided lasers
- Many excimer lasers are
connected to a device that
detects and "maps" defects
in the eye's optical system,
based on how lightwaves
travel through the eye.
These wavefront devices
individually guide the way
the eye's cornea is reshaped
to achieve a custom LASIK
ablation. Both slit scanning
and spot scanning lasers
have the ability to be used
for wavefront-guided
treatments.Wavefront-guided
lasers - Many excimer lasers
are connected to a device
that detects and "maps"
defects in the eye's optical
system, based on how
lightwaves travel through
the eye. These wavefront
devices individually guide
the way the eye's cornea is
reshaped to achieve a custom
LASIK ablation. Both slit
scanning and spot scanning
lasers have the ability to
be used for wavefront-guided
treatments.
Excimer Lasers and Eye
Tracking
Most modern excimer lasers
have automated eye tracking
systems to keep the laser
beam on target. Studies have
shown that eye trackers
produce better outcomes and
decrease LASIK complications
compared with past lasers
that did not use eye
tracking systems.
Indications and Features of
Excimer Lasers
In the following chart, OZ
stands for optical zone,
meaning the maximum size of
the pupil allowing light to
pass through the eye that
can be targeted effectively
for correction with a
specific laser. TZ stands
for the maximum treatment
area, including a transition
zone that can be used in an
ablation to achieve vision
correction in the targeted
area.
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Modern
FDA-Approved
Excimer Lasers |
|
Model |
Indications |
Type of Laser
Beam |
Optical Zone
(OZ) and
Treatment Zone
(TZ) |
FDA Approval
Year |
|
Alcon
LADARVision 4000
& CustomCornea
(laser plus
wavefront device
to guide laser)
|
Myopia: up to
-8.00 D with or
without
astigmatism (up
to -4.00 D)
Hyperopia and
hyperopic
astigmatism: up
to +5.00 D (near
vision problems)
and astigmatism
causing distance
vision problems
up to -3.00 D |
Scanning
spot
(0.8 mm)
|
OZ:
5.5 mm
TZ:
7.5 mm
|
2002 (myopia
with or without
astigmatism)
2006 (hyperopia
and
hyperopic
astigmatism)
|
|
Bausch & Lomb
Technolas 217A
and
Technolas 217z
Zyoptix (laser
plus wavefront
device to guide
laser, approved
2003) |
Myopia: up to
-12.00 D with or
without
astigmatism (up
to -3.00 D)
Hyperopia: up to
+4.00 D with or
without
astigmatism (up
to +2.00 D) |
Scanning
spot
(2.0 mm) |
OZ:
6.0 mm
TZ:
7.0 mm |
2000
(myopia
from -1.00
to -7.00 D)
2002
(myopia up
to -11.00 D)
2003
(hyperopia
with or
without
mixed
astigmatism) |
|
Carl Zeiss
Meditec MEL 80 |
Myopia: up to
-7.00 D with or
without
astigmatism (up
to
-3.00 D) |
Scanning
spot
(0.7 mm)
Gaussian profile
with more energy
applied
centrally |
OZ:
6.0 to 7.0 mm
TZ:
7.7 to 8.9 mm |
2006
(myopia
with or
without
astigmatism) |
|
Nidek EC-5000 |
Myopia: -1.00 to
-14.00 D with or
without
astigmatism
(less than 4.00
D)
Hyperopia: +0.50
to +5.00 D and
up to +2.00 D
astigmatism |
Scanning
slit
(7.0 x
2.0 mm) |
OZ:
5.5 mm
TZ:
7.0 mm |
2000
(myopia
from -1.00
to -14.00 D)
2006
(hyperopia
and hyperopic
astigmatism) |
|
Visx Star S4
& WaveScan
WaveFront
System (laser
plus wavefront
device to
guide laser) |
Myopia: up to
-6.00 D with or
without
astigmatism (up
to
-3.00 D) |
Variable
scanning
spot beam
(0.65 mm
to 6.5 mm) |
OZ:
4.0 to 9.0 mm
TZ:
4.5 to 9.5 mm |
2003 |
|
Visx Star S4 IR
& CustomVue
(laser plus
wavefront
device to
guide laser) |
Myopia: up to
-6.00 D with or
without
astigmatism (up
to
-3.00 D)
Hyperopia: up to
+3.00 D and up
to +2.00 D of
astigmatism
Mixed
astigmatism:
up to 5.00 D |
Same as
S4 |
OZ:
6.0 mm
TZ:
9.0 mm |
2005 |
|
WaveLight
Allegretto
Wave |
Myopia: up to
-12.00 D with or
without
astigmatism (up
to -6.00 D)
Hyperopia: up to
+6.00 D with or
without
astigmatism (up
to +5.00 D, not
exceeding mean
spherical
equivalent or
total refractive
error of +6.00
D)
Mixed
astigmatism: up
to 6.00 D |
Scanning
spot beam
(0.95 mm) with
emphasis
on applying
more energy
centrally
(Gaussian
profile) |
OZ:
4.5 to 8.0 mm
TZ:
5.2 to 8.7 mm
for spherical
treatments;
7.0 to 9.0 mm
for cylindrical
and spherico-
cylindrical
treatments |
2003
(myopia
and
hyperopia)
2006
(mixed
astigmatism) |
|
WaveLight
Allegretto
Wave With
Allegro Analyzer
(laser plus
wavefront device
to guide laser) |
Myopia: up to
-7.00 D with or
without
astigmatism (up
to 3.00 D)
Mixed
astigmatism: up
to 6.00 D |
Same
as
Allegretto Wave |
OZ:
Same as
Allegretto
Wave
TZ:
Same as
Allegretto
Wave |
2006
2007
(mixed
astigmatism) |
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Note: D refers
to diopters.
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Pupil Size, Ablation Speed,
and Patient Comfort
In recent years, increasing
evidence has indicated that
the zone where laser energy
is applied to reshape the
eye during LASIK may be too
small to accommodate larger
pupil sizes. If your pupil
expands in low light beyond
the zone where the eye was
reshaped (ablated) for
vision correction, you may
have vision problems such as
glare and halos at night.
Some surgeons believe the
diameter of the zone where
laser energy is used
(ablation zone) should be at
least as large as your pupil
in dim light. If you have
larger pupils, the type of
excimer laser may be
important in relation to how
large an optical zone the
machine is capable of
creating. You should discuss
this with your surgeon.
Ablation times also differ
among lasers, ranging from
30 to 60 seconds or longer.
You may consider that
important in terms of your
comfort as you undergo a
procedure.
Again, no matter which laser
is used, remember that
ultimately your surgeon's
skill and experience likely
will be the most important
factors affecting your LASIK
outcome.
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