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Clinical
Experience with the Allegretto Wave in Custom and Standard Treatments
Raymond Stein, MD, FRCS(C)
The Allegretto laser with its
"wavefront-optimized" ablation produces outcomes that rival custom results
with other lasers.
In June 2002 I began a clinical trial
with the Allegretto Wave™ excimer laser system (marketed in the US by
Lumenis, Santa Clara, CA). Two months later, I gladly paid full list price
to bring this technology in-house on a permanent basis.
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FIGURE 1A The Allegretto Wave incorporates a
slit
lamp, which adds to its versatility and ease of use. |
Today, 98% of my laser vision correction surgery is
performed with the Allegretto, and in the 18 months since procuring it, I
and my colleagues at the Bochner Eye Institute have used it for more than
3,000 procedures. The speed with which this system gained our favor is a
testament to the precision and functionality of its technology, as well as
to the quality of the outcomes.
I began performing laser vision correction surgery in
1991 and since then have completed thousands of procedures. Over this
period, I have purchased a number of excimer laser systems, starting with
the VISX 20/20 B and then lasers from Nidek, LaserSight, and, in sequence,
the Visx Star S2™, S3™, and most recently the S4™. The Allegretto Wave
system has a number of unique technological features that distinguish it
from other platforms I have used and which account, I believe, for the
outstanding clinical results we have achieved with it.
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 Ergonomic
Design
The Allegretto Wave fits easily in the confines of the typical
surgical suite. Yet despite its compact footprint, it is ergonomically
efficient, allowing the surgeon ample working room, especially while
operating the microkeratome.
Just as important from my perspective, the unit is a
solid, steady performer day in and day out. It maintains a very stable
fluence during an entire day's work, as well as from day to day and week to
week. With only routine maintenance, we have had very little downtime over
the past year and a half with this machine. Our technicians are happy with
the machine because it is so easy to calibrate. For an extremely busy
practice like ours, the Allegretto makes a superb workhorse laser.
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Outstanding Optics
The Allegretto's optics are the best of any laser I have ever used, thanks
to an integral slit lamp that provides excellent visualization. Without
removing the patient from the laser, I can easily detect striae, debris
underneath the flap, air bubbles, superficial punctate keratitis, and other
unwanted phenomena, should they appear at the time of surgery.
For enhancements, I no longer need to mark the flap
edges at a slit lamp and then bring the patient into the surgical suite. The
Allegretto's slit lamp attachment allows me to readily detect the flap edge
and simply lift it with no need for advance prep.
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Rapid Treatment Speed
Firing at 200 Hz, the Allegretto is the fastest laser on the North American
market. It is possible to complete a 1.00-D ablation with a 6.5-mm optical
zone in just 4 seconds. This is three times faster than a laser with a
similar spot size that fires at 60 Hz.
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FIGURE 1B The Allegretto Wave's small
footprint is easily seen in this top view. |
Shortening the treatment time increases the
predictability of outcomes. The longer the ablation, the more the stromal
bed dehydrates and the higher the likelihood of predictability-confounding
issues, such as flap edema and striae. Faster treatments are also less
demanding for the patient. Fixation time is shorter, and the anxious period
while the laser fires is also reduced.
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Fast, Easy Tracking
The Allegretto employs a 200-Hz synchronous eye tracker that is extremely
easy for the surgeon to use. There are no buttons to push - the tracker
automatically locks onto any undilated pupil that is between 1.8-8mm in
size. If needed, the tracker adjusts automatically to changes in pupil size
during the ablation.
To date, with over 3,000 ablations performed, we have
not had one instance in which we could not track an eye. This includes
several cases of rapid jerk nystagmus, all of which were completed without
difficulty or adverse impact on the outcome.
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Smooth Stromal Surfaces
With a 0.95-mm Gaussian spot, the Allegretto
delivers very precise tissue removal. It leaves a stromal surface that is
extremely smooth compared to a flat-top beam, and the small spot size is
perfectly compatible with the requirements of wavefront-guided ablation. In
addition, Allegretto places five other pulses between each overlapped pulse,
so there is less thermal effect on the stroma.
Surface ablation provides the truest test of
post-ablation stromal bed quality. In the old days of surface ablation, haze
was a frequent complication. In my experience with surface ablation using
other laser platforms, there was a 3-5% incidence of visually significant
haze. In over 300 cases of surface ablation performed with the Allegretto,
we have not seen a single case of significant corneal haze - even in myopes
requiring 6-9 D of correction. This is attributable, in my opinion, to the
Allegretto's extremely smooth ablation stromal surface it produces makes the
Allegretto an excellent performer for this most demanding of applications.
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Wavefront-optimized
Ablations
A wrinkle for US surgeons is that the Allegretto is not yet FDA-approved for
custom ablation. (Custom treatment with the Allegretto is available in other
parts of the world, including Canada.) Given the significantly better
results that US lasers are producing in custom mode, it's worth asking
whether purchasing the Allegretto could make sense for US surgeons.
Surprisingly, the answer appears to be yes.
WaveLight describes its standard (noncustom) ablation
pattern as "wavefront-optimized." In it, additional pulses are delivered to
the periphery of the ablation zone in order to maintain the proper corneal
asphericity. The steeper periphery means a more prolate shape, which
minimizes the spherical aberration induced by other lasers.
The bottom line is that "wavefont-optimized" outcomes
in the US FDA clinical trials (and in my personal experience) rival custom
outcomes with other lasers. Indeed, in head-to-head comparison with the
Allegretto laser, custom results were essentially the same as traditional,
except in the case of eyes with irregular astigmatism and/or high levels of
higher order aberration.
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Custom vs. Standard
Ablations
With all the buzz about custom ablation, results with the Allegretto's
wavefront-optimized ablation raise an important question: Art the improved
outcomes from custom ablation the result of wavefront technology alone? Or
are they attributable in small or large measure to other changes in the
laser systems themselves (e.g., refined algorithms) that the companies made
at the same time they added wavefront capability?
|
For an extremely
busy practice like
ours, the Allegretto
makes a superb
workhorse laser |
Let's consider an example: the standard and customized
ablation options offered by the Visx Star S4. The standard ablation uses a
broad beam, with each pulse centered over the pupil. The algorithm
automatically incorporates a compensatory prophylactic central island
treatment - although this is only necessary in about 20% of patients. So,
some of the remaining 80% will end up with a central divot and a mild
overcorrection (which usually reverses after a number of months). Similarly,
the standard ablation profile for a pure astigmatic correction offers a
short meridian of only 5 mm, which is relatively small and limits results.
In contrast, the Visx Star S4's customized ablation
utilizes variable spot scanning and a change in shot pattern delivery so
that each pulse isn't necessarily centered over the pupil. this allowed Visx
to eliminate the prophylactic central island treatment form the algorithm.
The custom ablation also incorporates a larger optical zone, so if one has a
pure astigmatism case, the sort meridian is greatly enlarged compared to
that of the standard treatment. These are very significant improvements that
would improve results even if there were no wavefront component.
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Is it All in the Laser?
So, are the better results we see with customized ablation primarily the
result of wavefront technology? Or are they, at least in part, the result of
other incremental enhancements to the laser? This is an open question.
Clearly wavefront has an important role in cases of significant corneal
asymmetry. However, my own instincts and results tell me that
wavefront-guided treatments are not required for all my patients. In my
experience, the patients who receive clinically significant benefit from
custom treatment are the very few who have preoperative troubles with glare
or halos and/or significant higher order aberration.
When the treatment population is essentially normal
eyes, there is very little difference observed between eyes treated with the
Allegretto's standard (i.e., wavefront-optimized) mode vs. its true
wavefront-corrected mode. Even testing custom vs. wavefront-optimized
ablations in fellow eyes of essentially normal subjects, as I have done,
produces almost no significant difference. I suspect that a comparison of
standard Allegretto procedures and custom procedures performed on another
laser system will yield little significant difference in quality of
outcomes.
When to Call on Wavefront Technology
I treat 96% of the refractive patients I see with the Allegretto's standard
ablation. I turn to custom ablation only when faced with complicated eyes.
These would include patients who have significant higher order aberration,
typically an rms value greater than 0.35 microns or complications
from prior refractive or corneal transplant surgery.
Having the wavefront option is essential not only for
this 4% with special needs but also for our practice to compete in a very
mature refractive surgery market where custom ablation is readily available.
But the reality of the situation is that, based on the outstanding clinical
results we achieve with the Allegretto's wavefront-optimized ablation, we
reserve the more time-consuming custom treatments for the small number of
complicated eyes we treat.
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THE
BOTTOM LINE |
| In our practice, the
Allegretto Wave excimer laser quickly became the machine of choice
for almost all of our surgeries because of its reliably excellent
outcomes as well as a number of ergonomic and technical features.
Easy to use and maintain, this system offers exceptionally fast,
smooth ablations, with highly accurate, reliable tracking that
contributes greatly to the quality of patient outcomes. The
Allegretto's standard ablation is wavefront-optimized so that we
reserve custom treatments for the roughly 4% of patients who have
complicated optical issues. |
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Raymond Stein, MD, FRCS(C), is medical
director of the Bochner Eye Institute, an assistant professor of
Ophthalmology at the University of Toronto, and president of the Canadian
Society of Cataract & Refractive Surgery.
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