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| Wavefront-guided laser ablation for custom Lasik and other
refractive eye surgery has been a significant improvement
for most individuals, but not for all |
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WaveLight Allegretto Eye-Q
Visx CustomVue iLasik
LADARVision CustomCornea
Bausch & Lomb Zyoptix
Learning if you would do fine with conventional refractive surgery or if you require wavefront custom Lasik, Bladeless Lasik, LASEK, PRK, or Epi-Lasik is much easier than it may at first appear, however
it is important to understand what wavefront custom Lasik, LASEK,
PRK, and Epi-Lasik is, and what it is not. As a general rule, the
quality of vision with wavefront is superior to conventional laser
eye surgery, but that does not mean that wavefront Lasik is best
for everybody. Individual circumstances will vary.
The primary difference between conventional Lasik and wavefront
custom Lasik is the mapping system that guides the laser. Wavefront
can be used for virtually all laser eye surgery techniques including
Bladeless Lasik, Lasik, PRK, LASEK, and Epi-Lasik.
Old Science, New Application
Wavefront is a very old technology that has only recently been
applied to human vision. Wavefront has been used for years by astronomers
who need to adjust the optics of their telescopes. A reflecting
mirror within the telescope that can be deformed is adjusted using
wavefront data to eliminate aberrations induced by the Earth's atmosphere.
In wavefront custom Lasik, PRK, LASEK, and Epi-Lasik, the excimer laser uses wavefront information to change the shape
of the cornea by ablating tissue.
Wavefront Diagnosis and Wavefront Treatment
Wavefront is actually used in two separate ophthalmic events. The first is a wavefront evaluation and diagnosis of existing
aberrations. The second is using what is learned from the diagnosis
to create a wavefront-guided ablation for Lasik, PRK, LASEK, or
Epi-Lasik.
Our organization has included wavefront diagnostic as
a must-do in our 50 Tough Question For Your Doctor, but we have not included
it for guided ablations. A wavefront diagnostic can determine if
an individual has aberrations that would be exacerbated by refractive
surgery to the point of causing vision problems. No other technology
can achieve this level of diagnosis. Wavefront diagnostic can determine
if a wavefront guided ablation is an absolute requirement, conventional
ablation would be fine, or the patient should not have surgery at
all. This is why we believe wavefront diagnostic is an important
evaluation.
Several Laser Options
In the United States, there are four wavefront responsive laser
manufacturers. The trade names are CustomCornea using the Alcon
LADARVision laser, CustomVue using the Visx S4 laser, and Zyoptix
using the Bausch & Lomb Technolas 217z laser. These lasers have the
ability to create an ablation customized from an individual patient's
wavefront evaluation.
The Wave Light Allegretto laser used wavefront derived data in
the laboratory to optimize its laser ablation pattern, but does
not use an individual patient's wavefront diagnosis to create a
customized ablation pattern. CustomVue, CustomCornea, and Zyoptix
are all customized to the individual's eye. Visx, Alcon, and B&L
refer to their systems as "custom wavefront". Allegretto is referred
to as "wavefront optimized".
Square Grid In, Wavy Grid Out
During a wavefront diagnosis, light is sent into the eye in a
specific pattern, then measured after it has passed through the
visual system. Any difference between what goes in and what is measured
is considered an aberration. Think of a square grid going in and
a wavy grid coming out. The waves represent aberrations.
Higher Order Aberrations
A common eye examination and refraction evaluates low order aberrations (LOA). These are commonly called
sphere (myopia,
nearsighted, shortsighted or hyperopia, farsighted, longsighted) and cylinder (astigmatism).
Only a wavefront diagnosis is able to measure high order aberrations
(HOA), which are beyond simple sphere and cylinder. HOA are represented
in mathematical calculations and are therefore infinite. The more
common of these mathematical calculations are Zernike polynomials and have names like spherical aberration,
coma, trefoil, and quatrefoil. Ophthalmology only deals with about
the first eight levels of HOA as represented in Zernike.
Wavefront technology as a diagnostic device is unsurpassed. This
technology can diagnose and measure aberrations that no other system
can even see. It is important to understand that without a wavefront
diagnosis, it is impossible for a doctor to accurately determine
if wavefront-guided ablation is necessary for a good Lasik, PRK,
or LASEK outcome. Also, without a wavefront diagnosis it is impossible
for a doctor to accurately determine if a wavefront ablation is not necessary. In other words, virtually every person considering
Lasik, LASEK, PRK, or Epi-Lasik should have a wavefront diagnostic
evaluation.
Detailed Mapping
Think of an eye examination as a way to "map" vision limitations.
A conventional eye exam can map LOA. A wavefront diagnostic can
map LOA and HOA. Laser eye surgery based upon the LOA determined
with a conventional eye exam is like using a map of your state to
find your way around. That works pretty well if you are trying to
get from Los Angeles to San Francisco. Custom wavefront could be
compared to a map of your city. It can help guide you to a specific
street corner. Custom wavefront-guided Lasik, LASEK, PRK, and Epi-Lasik
directs the excimer laser to change the shape of the cornea using
a more detailed mapping system than conventional refractive surgery.
Human vision provides some unique challenges for application
of wavefront technology. The human eye is not a telescope. The eye
is dynamic, with ever changing focus, pupil size, and other normal
biological fluctuations. A telescope is static and once adjusted
for a certain set of aberrations, never changes. A deformable mirror
can be adjusted to a very precise amount. Ablating corneal tissue
is not nearly so precise. Wavefront may be an excellent mapping
system, but that does not necessarily mean that you can get to where
you want to go.
HOA are divided into separate terms and some HOA are much more
important to good quality vision than others. Spherical aberration,
coma, and trefoil are examples of HOA that are very important to
keep low. An HOA measurement often used is Root Mean Squared (RMS).
RMS is more or less an average of all HOA. Having a low RMS is good,
but if you have an elevated HOA that is one of those that is known
to cause vision quality problems, a low average may not be enough.
As an example, if you have low HOA RMS, but a high spherical aberration,
wavefront-guided surgery may be a requirement. You will need to
discuss this issue in detail with your doctor. Wavefront-guided
refractive surgery is FDA approved for a wide range of correction, but this is a range
that does have limits. If you are too myopic, too hyperopic, or
have too much astigmatism, you may not be eligible for wavefront-guided
Lasik, PRK, LASEK, or Epi-Lasik.
Ablate Deeper
Wavefront-guided ablations may remove more tissue than conventional
ablations, depending upon the unique circumstances of the individual
patient. If you have thin corneas, additional tissue removal may
be an issue. For more information, see Thin Cornea.
The size of the fully corrected optical
zone is limited for wavefront-guided ablations. If your naturally
dilated pupils are unusually large, you may have an increased risk
of poor vision in low light environments. See Lasik and Pupil Size
Monovision Limitations
If you are considering monovision correction, it will may be necessary to use conventional
Lasik, PRK, LASEK, or Epi-Lasik rather than wavefront-guided. Current
wavefront-guided lasers are very limited in their ability to undercorrect.
It's full correction or nothing at this time. While the non-dominant
eye will need to be undercorrected with a conventional ablation,
the dominant eye may be fully corrected with a wavefront-guided
ablation. Undoubtedly, each of the manufacturers will eventually
allow their lasers to undercorrect in wavefront-guided mode.
Better, Not Perfect
Something very important to understand is that not all aberrations
are reduced with custom wavefront or wavefront optimized Lasik,
PRK, LASEK, or Epi-Lasik. In fact, in all refractive surgery procedures,
wavefront or conventional, HOA tends to increase. This is one of
the reasons that the FDA has approved the use of wavefront-guided
ablations, but has not specifically approved any laser to actually
treat and reduce HOA. Our organization distributed a special Advisory
Memorandum regarding this issue. See FDA HOA Advisory.
It has been shown, however, that CustomVue, CustomCornea, and
Zyoptix increase HOA less than conventional ablations. This is also
true of Wave Light. HOA may increase no matter what you choose,
but it will probably increase less with wavefront. Because HOA is
likely to increase, if your natural HOA are already elevated, refractive
surgery may elevate them farther and cause poor vision. In this
situation, it may be that no corneal-based refractive surgery is
appropriate.
Get Out Your Credit Card
Let's not forget cost. Many doctors charge more for wavefront-guided
refractive surgery than conventional. Although no one should compromise
their vision for a little cost savings, paying less for surgery
is usually preferred over paying more.
If you meet all other requirements, there is nothing that indicates
wavefront-guided Lasik, LASEK, PRK, or Epi-Lasik will provide an
outcome that is inferior to similar conventional surgery, and there
are many indications that wavefront-guided surgery will provide
a superior outcome. However, there are absolutely no guarantees
in surgery and refractive surgery is no exception. Any prediction
of your actual outcome will be based upon past experience and reasonable
evaluations, but no one will know for sure until after surgery.
You may want to see Lasik
Outcomes.
Wavefront Diagnostic For Every Patient
Everyone considering any corneal-based refractive surgery, such
as Lasik, LASEK, PRK, or Epi-Lasik should have a wavefront diagnostic.
A wavefront diagnostic will determine if critical HOA are below
normal, normal, or elevated. If the HOA are elevated, either wavefront-guided
surgery is required, or no surgery is appropriate. If HOA are normal,
wavefront-guided surgery may be wise. If HOA are below normal, wavefront-guided
continues to be an option, but not a requirement. This is assuming,
of course, that you meet all other requirements for wavefront-guided
Lasik, LASEK, PRK, or Epi-Lasik laser eye surgery.
Looking For Best Lasik Surgeon?
If you are ready to choose a doctor to be evaluated for conventional
or custom wavefront Lasik, Bladeless Lasik, PRK, or any refractive surgery procedure, we recommend you consider a doctor who has been evaluated and certified by the USAEyes nonprofit organization.
Locate a USAEyes Evaluated & Certified Lasik Doctor.
Personalized Answers
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