Lasik applies laser energy under a flap of corneal
tissue to correct nearsighted vision, farsighted vision,
and astigmatism. Click for video.
Lasik is the most often performed
surgery in the US. Conventional or wavefront custom Lasik is a surgical procedure that changes
the shape of the cornea to reduce the need for glasses or contacts. Lasik has
many distinct advantages over other refractive surgery procedures, but also has limitations that
may indicate something else or no surgery is best for an individual
The most you can expect from Lasik is the convenience of a reduced
need for corrective lenses. To achieve that convenience, you must
accept some risk. We hope to help you minimize that risk, but risk
cannot be eliminated.
This document discusses in detail the history of Lasik, some
of Lasik's advantages, and many of Lasik's disadvantages. This long
and detailed article is to help a potential Lasik patient understand
in depth what Lasik can do, might do, and when it is likely to do
what is desired. Much of this discussion compares Lasik with other
refractive surgery procedures, including PRK, LASEK, Epi-Lasik, P-IOLs, and RLE.
The primary difference between Lasik and other cornea based procedures
is where the excimer laser ablates: under a flap of corneal tissue. Lasik
is actually the combination of Photorefractive Keratectomy (PRK)
and Automated Lamellar Keratoplasty (ALK).
As you will see, the Lasik flap is both Lasik's strength, and its
As with nearly all excimer laser based refractive surgery, Lasik
can be performed with both conventional ablation and wavefront-guided ablation.
In The Beginning
ALK was developed in the 1950s as a method of refractive surgery.
A mechanical microkeratome is affixed to the eye with a suction ring. A plate
flattens the cornea and a very sharp metal blade passes through
the top of the flattened cornea, creating a thin slice of tissue.
In original ALK, additional shavings of the cornea were removed
to cause a net flattening of the central cornea. Flattening the
center of the cornea will cause a change in the way light bends
through the cornea, correcting myopia (nearsighted, shortsighted). The more tissue that is
removed, the more the center becomes flat, and more refractive correction
ALK was refined over the ensuing decades, but complexity of the
microkeratome, unpredictable results, and difficulty of the procedure
kept its adoption out of the mainstream. The development and popularization
of Radial Keratotomy (RK)
in the 1980s provided a more reliable means to correct refractive
error, although ALK still had its fans in ophthalmology and the
technology behind ALK continued to advance.
The Laser Is Introduced
Lasers have been used successfully for eye care for decades.
A laser is only highly condensed light and just about everything
your eye doctor does deals with light. PRK was the first refractive
treatment to use an excimer laser to remove tissue. An excimer laser
changes the chemical nature of the molecules that hold together
the cells of the cornea. The change causes this "glue" to release
the corneal cells, and they rapidly escape from the cornea in a
plume that looks very much like an atomic bomb blast, but is significantly
different in its cause and effect. The excimer laser does not "burn"
the cornea or cut the cornea. It makes the corneal fall apart, microscopic
layer by microscopic layer. You cannot talk about Lasik without
talking about PRK. Detailed PRK
The Cornea Responds
A major problem with PRK in its early development was corneal
haze. PRK related haze continues to be a problem to this day, although
some techniques have been developed to control its severity and
treat its occurrence. Corneal haze is caused by the cornea's wound
response. Surgery is an insult to the cornea, and your cornea really
doesn't care if you want this insult, it is going to respond as
if it has been wounded. A part of that wound response causes opaque
cells to form. This presents as white hazing of the cornea, restricting
light from passing through, and reducing the quality of vision.
PRK haze does not normally form for corrections that require
a moderate amount of tissue removal, generally less than about 6.00 diopters of refractive error. That is good news for moderate and low myopia
and virtually all hyperopes (farsighted, longsighted), but bad news for those
needing higher corrections. As a general rule, if you need less
than 6.00 diopters of correction, you should consider PRK as an
Different Depths, Different Responses
It was noted that wound response to laser ablation deeper in the cornea is significantly different than
when the ablation is performed at the outer surface of the cornea.
The idea was formed to creating a flap of corneal tissue using ALK
methods, perform the PRK ablation under the flap and deeper in the
cornea, then returning the flap over the ablated area. Thus Lasik
was created as a combination of ALK and PRK.
Lasik literally "fools" the cornea into not knowing it has been
wounded. This is why Lasik normally provides no pain, has an almost
instant vision recovery, and almost never causes corneal haze; the
cornea doesn't know it has had surgery. You could call this microsurgery's
own "ignorance is bliss". This major advancement allows correction
of very high refractive error without a high risk of corneal haze
and subsequent loss of vision quality.
More Than One Way To….
Due to new demand caused by the creation of Lasik, rapid advancement
in mechanical microkeratome technology has provided much better
quality corneal flaps with more predictability of size and thickness.
Additionally, the femtosecond laser has been refined to create flaps
with laser energy, rather than a metal blade. Intralase is the first company to introduce this technology to the US and
Lasik with a laser created flap is often called Bladeless Lasik
or "all laser Lasik". Detailed
Bladeless Lasik Information
Not All 20-Minute Miracles
The only way to describe the implementation and popularity of
Lasik is as an explosion. Ophthalmologists were rushing to lean
how to perform this new procedure that promised to give patients
freedom from glasses with no pain and almost instant results. Patients
were flocking to clinics looking for freedom from glasses and contacts.
That was the theory of what would happen. There is nothing that
can screw up a perfectly good theory faster than reality.
Reality Sometimes Bites
While the vast majority of patients received a seemingly miraculous
improvement in uncorrected vision, a small but very important minority
had complications ranging from nuisance to vision debilitating.
Much was learned by the early problems with Lasik. The range of
refractive error treated today is significantly more narrow than
in the early years. You will virtually never see a 20.00 diopter
myope have Lasik today. This was not always the case.
Refinements in technology and technique have reduced the severity
and probability of complications, but even with continued refinement,
no surgery is perfect and there will always be some who will have
unexpected and undesired outcomes. The primary purpose of the our
organization is to help prospective patients become informed of
the issues that contribute to poor outcomes, avoid those problems,
and find the best qualified doctor available.
Back To The Future
The basics of Lasik today are virtually the same as when first
created: make a flap, zap the cornea, and replace the flap. The
range of variables in this three-step process is ever increasing,
as are the number of options. What we discuss here are some of the
options available today – old and new – and their relative advantages/disadvantages.
If you visit our article on Intralase, you will learn the details
of the creation options of the corneal flap, but all flaps have
potential problems, no matter how they are made. The first problem
of the Lasik flap is the existence of the flap itself.
If the flap exists, there will be the possibility of flap related
problems. Those potential problems do not stop when you leave the
surgery suite. Once you have had Lasik you have always had Lasik
and you must always consider that your eye is fundamentally and
forever changed. Change can be a good thing, but sometimes not.
There is a movement in ophthalmology back toward the surface
ablation techniques of PRK and its cousins LASEK and Epi-Lasik because
surface ablation eliminates the Lasik flap. If you eliminate the
flap, you do not just reduce the possibility of a flap complication,
you eliminate it completely. Everybody likes eliminating the possibility
of a problem.
The advantage of surface ablation techniques go beyond just eliminating
the possibility of flap complications. Study after study have shown
that PRK produces long-term results that are equal to or superior
than Lasik. A part of the reason for these better outcomes is the
availability of enhanced ablation patterns with wavefront technology. Long term, PRK is often better for a patient
than Lasik. The problem is, we don't "see" long term.
Lasik and PRK Recovery
The recovery from PRK is vastly different than Lasik. With Lasik,
it is probable that fully functional vision will be almost instantaneous,
there will be almost no pain, and you can resume most normal activities
almost immediately. PRK, on the other hand, provides "fuzzy functional"
vision for 3-6 days, functional vision for about another 2 weeks,
and you won't get the really good crisp vision you desire for about
6-8 weeks after surgery. Not everyone can afford this much time
with compromised vision. There is much more discomfort associated
with PRK, and even today PRK has limitations due to haze, but let's
consider how the haze situation has improved.
LASEK and Epi-Lasik
The ideal situation would be to have surface ablation with no
pain, little probability of haze, and instant recovery. In other
words, Lasik without the flap that reduces the probability of these
limitations and speeds vision recovery. The answer to Lasik without
the flap may be in changing the depth the flap.
The epithelium is the outermost layer of the cornea. These are the
fastest reproducing cells in the human body. Before the laser can
remove corneal tissue with PRK, all epithelial cells must be removed
over the treatment area. The epithelial cells will regenerate and
cover the treatment area in about 3-6 days. They will thicken over
the ensuing 2 weeks, and smooth at about 6-8 weeks. Those time periods
sound familiar? That's right, all the slow vision recovery of PRK
is directly related to the epithelium recovery. Also, comfort is
related to epithelium recovery.
Save The Epithelium!
Obviously, if the epithelium is so helpful, it needs to be saved.
Lasik leaves the epithelium in place because the Lasik flap is cut
deep underneath the epithelium in the deeper stromal layer of the cornea. Two similar but separate techniques
to save the epithelium have been developed; LASEK and Epi-Lasik.
In LASEK, a diluted solution of alcohol is applied to the cornea
for a few seconds. This disrupts the epithelial cell's ability to
hold on to Bowman's
layer, the next layer down the corneal construction. These disrupted,
but viable, cells are moved out of the way, the laser does its magic,
and then the cells are moved back over the treatment area. In theory,
LASEK will hasten recovery, limit pain, and reduce the probability
of haze. I'm sure you remember what we said about theories.
The reality is that few of the epithelial cells survive the alcohol.
While the dead or dying cells replaced over the treatment area do
provide extra protection and appear to reduce discomfort, vision
recovery is not significantly improved. Improved, yes, but nothing
like a Lasik recovery. While a reduction in corneal haze was noted,
this may be attributed more to the advancement in laser quality
than the LASEK procedure. Doctors are seeing less haze with PRK
today, even thought PRK does not keep the epithelium. Detailed LASEK
The latest in the attempt to save the epithelium is Epi-Lasik.
This technique uses a mechanical microkeratome with a blunt, rather
than sharp, blade that slides across the front of the cornea. This
blunt blade scrapes up a sheet of epithelium at the surface of the
stronger Bowman's layer. This is essentially an epithelial flap.
The flap is moved out of the way similar to Lasik, the laser treats
the exposed area, and then the epithelial flap is repositioned.
Early reports indicate that there is improvement in recovery time,
comfort, and even the probability of haze, but it is much too early
to know if Epi-Lasik is really ready for prime time. Detailed
Detailing the Details of Detailed Ablations
If you are considering Lasik, you are going to hear about wavefront.
You are going to hear a lot about wavefront. You are going to be
inundated with wavefront this and wavefront that. Click Wavefront Guided Ablation for a detailed article about whether
or not you require a wavefront-guided ablation. In this article
we will discuss how wavefront-guided ablation relates to Lasik.
Using a wavefront-guided ablation is often called custom Lasik,
custom PRK, CustomVue, CustomCornea, or Zyoptix, depending upon
the laser used. The process uses a wavefront aberrometer to evaluate
virtually all of the optics that affect your vision. From this wavefront
derived information, an ablation profile is created with the intent
of reducing the introduction of harmful aberrations to your optics,
and reducing those that already exist.
Think of wavefront as a mapping system. If you wanted to travel
from Cleveland to Beverly Hills, a map of the whole US showing all
the major highways would do just fine. If you wanted to get to a
specific street corner on Rodeo Drive, you would need the detail
of a city map. Think of conventional laser ablation as a map of
the US, and wavefront-guided ablation as a street map.
The wavefront ablation profile of where more tissue needs to
be removed here and less tissue needs to be removed there is very
nuanced with tiny changes across the treatment area. A problem with
Lasik is that you are putting a relatively thick 100-180 micron flap of corneal tissue on top of this fancy nuanced ablation. Like
too many blankets on the bed, you lose some of the detail of the
shape of who is in that bed.
Yet another reason why there is a push toward PRK in some circles
is that the lasers are now able to make these really nice detailed
ablations, but some of that detail is muted by the Lasik flap. Also,
the Bowman's layer and uppermost layer of cells of he cornea are
more dense than the deeper stromal layer. It is opined that this
may help in creation of better and better ablations.
Why Not Abandon Lasik For surface ablation?
At first glance, it would seem that everyone should be jumping
back on the PRK bandwagon. Not always. There is still that issue
of corneal haze. The newer lasers seem to reduce the probability
of corneal haze with PRK, but do not eliminate it. LASEK and Epi-Lasik
attempt to minimize the limitations of PRK by saving the epithelium,
but they may turn out to be just so much expensive luggage.
It has been found that having a patient take 500mg of vitamin
C (yes, plain old vitamin C) twice a day for a week before PRK and
at least two weeks after surgery significantly reduces the incidence
of corneal haze. Isn't it always the simple answer that is the best.
This appears to be helpful, but more study is needed to determine
just how much help is provided with oral vitamin C supplements.
It is really not known if vitamin C is enough for someone who needs
8.00 diopters of correction, but is not enough for someone who needs
10.00. The limits need to be determined.
The use of the topical eye drop Mitomycin C dramatically reduces
the probability of haze, and can be used to treat haze when it occurs,
but this is rather strong medicine. Mitomycin C is appropriate when
required, but probably needs to be avoided if possible. Also, Mitomycin
C changes how much tissue the laser ablates with each pulse, so
the doctor needs to manually change the treatment plan. This requires
Lasik & Many Options
To get the best possible outcome, one must play the odds. You
cannot guarantee perfection, but you and your doctor can take many
steps to reduce the probability of a bad outcome. Procedure selection
is one of those steps. It is not that Lasik is always best, or PRK
should be used whenever possible, it is more that depending upon
your unique circumstances, Lasik may or may not be the best choice
for you. There is nothing wrong with Lasik as a procedure, if it
is the best procedure for your situation.
As a gross generalization, Lasik is probably best for someone
with more than 6.00 diopters of correction, and almost certainly
necessary for someone needing more than 10.00 diopters of correction.
Less than 6.00 diopters would make PRK, LASEK, and Epi-Lasik added
possibilities. Between 6.00 diopters and 8.00 diopters, LASEK, Epi-Lasik,
or PRK with Mitomycin C would be added to the mix. If you require
fast recovery and can't handle even a small amount of discomfort,
then Lasik and possibly Epi-Lasik are the prime choices. Over 12.00
diopters of myopic correction and over about 3.00 diopters of hyperopic
correction would indicate that cornea based surgery is probably
not wise and alternatives such as P-IOLs or RLE should be considered. Although Lasik is approved for much
higher corrections, that does not mean that very high refractive
error should be corrected with Lasik in your case.
Remember, these are gross generalizations and upon examination
your doctor may recommend something completely different. And of
course, it may be that no refractive surgery of any kind is appropriate
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.
If this article did not fully answer your questions, use our
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