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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.

 

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 Wa
ve

OZ:
Same as
Allegretto
Wave

TZ:
Same as
Allegretto
Wave

2006

2007
(mixed
astigmatism)

Note: D refers to diopters.


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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