LASEK:Comparison to Lasik, All-Laser Lasik, Epi-Lasik, and PRK
LASEK
Comparison to Lasik, All-Laser Lasik, Epi-Lasik, and PRK
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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.
If you are ready to choose a doctor to be evaluated for conventional or custom wavefront Lasik, All-Laser Lasik, PRK, LASEK, Epi-Lasik, NearVision CK, RLE, or any refractive surgery procedure, we highly recommend you consider a doctor who has been evaluated and certified by the USAEyes nonprofit organization. Locate a USAEyes Evaluated & Certified Lasik Laser Eye Surgeon.
Video courtesy University of Illinois Eye & Ear Infirmary.
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