 Similar to PRK and Epi-Lasik, LASEK creates a flap
of the epithelium that is moved aside and replaced over
the area treated with the excimer laser. Click for video. |
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Laser Assisted Sub-Epithelial Keratomileusis (LASEK) is a refractive
surgery technique developed by Italian doctor, Massimo Camellin,
MD and first publicized in 1999. The motivation behind LASEK was
to find a surface ablation technique like PRK that induced less discomfort, offers a lower incidence of
corneal haze, and provides the patient with faster vision recovery
time.
To understand LASEK, on needs to understand a little about PRK
and conventional or wavefront custom Lasik.
Hazy View of Things
A major problem with PRK in its early development was corneal
haze. 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.
Combine Old With New
It was noted that wound response to PRK 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 virtually no pain, has an almost instant
vision recovery, and almost never causes corneal haze; the cornea
almost doesn’t know it has had surgery.
Moderate Correction = No Haze
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 (nearsighted, shortsighted) 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, LASEK will not offer a risk of
corneal haze any different than PRK. Above 6.00 diopters, LASEK
may have an advantage.
Old Reliable Vitamin C
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.
Strong Medicine
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
additional expertise.
It's All In The Flap
The concern between LASEK and Lasik is the Lasik flap. Although
it provides the patient with more comfort, virtually eliminates
the probability of haze, and offers very quick visual recovery,
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.
Another potential problem with Lasik is that severing the corneal
nerves deeper in the cornea often will temporarily induce dry eyes.
The signals from the cornea are interrupted until sensation returns
with healing. That can be weeks to months. Although fewer than 3%
of refractive surgery patients have any kind of unresolved
complication at six months postop, dry eyes is the temporary problem
most prevalent with Lasik.
Yet another issue with the thicker Lasik flap relates to the
ability to create more detailed ablation profiles with newer technology
like flying
spot gaussian beam excimer lasers and wavefront-guided ablations. 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. The limitation 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. 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 ablation in Bowman's layer
may help in creation of better and better ablations.
And if that was not enough, the Lasik flap is from 100 to 180
microns thick. If the patient has a thin cornea, there may not be
enough room for the Lasik flap, the tissue ablation, and the 250
microns of untouched cornea that is needed to keep stability and
reduce the probability of ectasia.
A Flap That's Not A Flap
The desire to eliminate potential Lasik flap related problems
brings us back to PRK, but PRK is not terribly comfortable for the
patient, has a longer recovery period, and there is that problem
with haze for higher myopes. The idea that Dr. Camellin had was
to create an "epithelial flap" that would fool the cornea the way
the thicker Lasik stroma flap does, but not be subject to the same
complications as a Lasik flap.
During PRK, the epithelium is removed and the excimer laser treatment occurs
on the underlying outermost surface of cornea. Rather than removing
the epithelium, LASEK attempts to save the epithelium by using an
alcohol solution to cause the epithelial cells to weaken. After
removing the solution from the eye, the doctor will lift the edge
of the weakened epithelial flap and gently fold it back out of the
way. The corneal epithelial cells are the fastest reproducing cells
in the human body. Even if destroyed by the alcohol solution, they
will quickly regenerate. After the epithelial flap is moved out
of the way, excimer laser energy is then applied through the Bowman's
Layer and into the upper stroma to reshape the cornea. When the
cornea has been reshaped by the laser, the epithelium flap is returned
back to its original position.
A contact lens is placed on the cornea shortly after surgery
as a bandage for several days to aid in the healing and the reduction
of pain. It normally takes three to ten days for the epithelium
to heal and resurface the cornea. This healing time varies depending
on a number of factors such as the size of the area treated, the
health of the patient's cornea, the individual's in healing rate,
and the toxicity of the medications and solutions applied to the
surface of the cornea.
Neither a mechanical nor laser microkeratome is used in Lasik is used in LASEK.
LASEK Flap Loss Means PRK
Sometimes when LASEK is attempted, the 50-micron thin epithelium
flap is not strong enough to be laid back over the treatment zone.
In these cases, the epithelium will be removed as it would have
been in PRK. In this situation the LASEK procedure becomes a PRK
procedure. If this happens and the patient was within the parameters
for PRK, there is no cause for concern because it will normally
not adversely affect the visual result. If the patient was a high
myope and LASEK was being used as a technique to reduce the probability
of corneal haze, then there may be a problem. Most doctors will
tell a LASEK patient that LASEK will be attempted but it cannot
be guaranteed that the LASEK will be completed - the epithelium
of each individual behaves differently.
Advantages and Disadvantages
Visual recovery after LASEK is generally faster than in PRK,
a little slower than Epi-Lasik, but significantly slower than Lasik.
The potential advantages of LASEK over PRK are a reduction of
postoperative discomfort, a decreased risk of infection, and decreased
incidence of corneal haze. Advantages of LASEK over Lasik include
elimination of the possibility of any stromal flap complications
during surgery or throughout the patient's lifetime, including striae,
DLK, and others, a decreased risk of temporary induced dry eyes,
and an increase in the overall thickness of the untouched area of
the cornea. Advantages of Lasik over LASEK include virtually no
pain with Lasik and almost instant clear vision, often called the
"WOW!" effect.
A progression of LASEK is Epi-Lasik. Epi-Lasik uses a mechanical microkeratome with a
blunt blade to slide across Bowman's and lift up a flap of epithelial
cells. This flap is not reduced in strength by an alcohol solution
and tends to be more stable than a LASEK flap.
The use of the excimer laser for LASEK is not FDA-approved, but
is an accepted "off
label use" use of the excimer laser. Lasik was also an off label
use of the excimer laser for many years and with some lasers continues
to be an off label use.
As with nearly all excimer laser based refractive surgery, correction
can be performed with both conventional ablation and wavefront-guided
ablation.
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.
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