||LASEK-THE NEW PRK|
EDITED REPRINT FROM EYENET MAGAZINE
LASEK GRABS THE SPOTLIGHT
Surface ablation of the cornea appears to be getting a second wind among refractive surgeons, thanks to the increasing interest in LASEK.
Physicians disagree on whether LASEK is indeed a new procedure or just a souped up version of PRK, but there’s no question that LASEK has sparked a reconsideration of PRK’s reputation. LASEK uses an alcohol solution to detach but preserve a sheet of epithelium from the cornea, creating a flap that can be peeled back to perform the excimer laser ablation. This creates a procedure with the advantages of different approaches: a stroma untouched by the LASIK microkeratome; less pain than is usually seen with PRK; and, in early studies, little or none of the corneal haze experienced with PRK.
TWEAKING AN OLD TECHNIQUE?
As a result, researchers around the world are trying to discern whether LASEK will remain a bit player on the refractive surgery stage- or should grab a starring role.
“ Sometimes it takes innovations like an epithelial flap to revitalize a technique and bring it to the next level”, said Daniel Durrie, MD. “This is like back when phacoemulsification was first introduced in the late 1970’s. It wasn’t until we introduced capsulorhexis, hydrodisection and small incision foldable IOL’s that phaco really came around and became the dominant procedure (for cataract surgery) years later.” Even so, Dr. Durrie is among those who believe LASEK merely tweaks an old technique. “This is surface ablation, and it is just the 2002 version of PRK.”
Eric D. Donnenfeld, MD is more blunt. “It’s a case of the Emperors New Clothes. Everyone is telling you that LASEK is so much better that you have to see it. And if you’re not seeing it, then you feel foolish. Bit it’s not the panacea people are saying it is. It’s an improvement over PRK in that there’s less discomfort, but I don’t know if the visual results are any better”.
AHEAD OF THE CURVE
The enthusiasm for LASEK has emerged largely as a result of individual physicians’ reports rather than through the gold standard for judging a new procedure-publication of large, randomized studies comparing it with competing techniques.
For instance, in the January issue of the Journal of Cataract and Refractive surgery, Thomas V Claringbold II, DO reported good visual results, no loss of BCVA and no serious complications in 222 eyes he corrected with LASEK. But Dr. Claringbold likes LASEK so much that he had no LASIK or PRK eyes for comparison.
In March 2001, an Italian study compared two groups of 15 patients each. Results indicated that LASEK patients had better corneal topography, BCVA and contrast sensitivity than did the LASIK patients.
Paolo Vinciguerra, MD has reported that he has performed LASEK 1,000 times and likes it so much that 85 percent of his current refractive surgeries are LASEK. However, Medline contains no citations on his results.
The physician with the longest experience is Dimitri T. Azar, MD. In 1996 he first performed a procedure he called "alcohol-assisted flap PRK." (Later it was renamed LASEK by Italian surgeon Massimo Camellin, MD, when he reported and popularized his version in 1999.)
Up to five years of follow-up (in a single patient) shows no unanticipated problems, but Dr. Azar still reserves LASEK for fewer than 10 percent of his patients. His group reported its results with 20 eyes in the August 2001 issue of Current Opinion in Ophthalmology.
"I was concerned that there could be some potential complications that are unique to this procedure—for instance, recurrent erosion syndrome, more scarring, more pain or refractive surprises," Dr. Azar said.
"But now that we have five-year data on our earliest patients, I am more confident that there won't be any surprises—not any more surprises than LASIK or PRK," he commented.
THE LASIK COMPARISON
If Dr. Azar's assertion holds, and if current studies show that LASEK results are comparable to those of PRK or LASIK, then the clinician would be left to weigh risks vs. benefits. But here, too, there is no unanimity. Some LASEK pros and cons to consider:
> PRO: Fewer complications. For Dr. Claringbold, LASEK is tops because it eliminates the sight-threatening flap complications of LASIK. "You can never have wrinkles in the flap. You can never have epithelial ingrowth or dislocation of the flap later with trauma. And essentially you're doing a better PRK but with less pain and no haze."
LASEK also means a physician wouldn't have to do a lot of refractive surgery to get reliably good results, Dr. Donnenfeld said. "If a doctor feels uncomfortable with the microkeratome and wants to avoid it, LASEK offers the perfect opportunity to do refractive surgery without the associated risk of flap complications from the microkeratome." The procedure lessens "that variable of complications caused by low volume," he said.
PRO: Deeper pool of candidates. LASEK can be offered to patients who otherwise couldn't undergo LASIK
CON: More pain, slower results. Some refractive surgeons think that patients will be reluctant to accept a procedure that has more pain and lacks the "Wow!" factor of LASIK. To control pain while the epithelial flap heals, LASEK patients must wear a bandage contact lens for about four days, and ultimate visual acuity takes up to several weeks to achieve.
THE PRK COMPARISON
Another barrier lies in today's PRK itself. "I'm going to probably try LASEK, but I just have been doing so well with my PRKs that I haven't been motivated to do so.” said Douglas D. Koch, MD. "PRK
is much better than it used to be, because the new lasers do such a good job of creating a smooth ablation surface."
Nonetheless, LASEK may have some advantages to consider:
PRO: Less pain. Because the epithelium is left intact, LASEK patients typically experience less pain than do PRK patients. However, some refractive surgeons note that pain control with PRK is improving, thanks in part to the use of new medications.
PRO: Faster healing. The intact epithelium heals faster—and some believe better—than it does in PRK. Other ophthalmologists who examine his post-LASEK patients usually remark that they can't see any evidence that the epithelium was ever disturbed, Dr. Claringbold said.
One hypothesis suggests that this is because the epithelial flap maintains a limbal connection, giving it access to limbal stem cells for better healing. This is the premise behind a new "butterfly" flap technique developed by Dr. Vinciguerra to preserve the epithelial connection to the limbus.
Instead of the U-shaped incision generally seen in LASEK, Dr. Vinciguerra makes a central, vertical cut, then
Spreads the epithelium open from the middle to do the ablation.
PRO: LESS HAZE. Another hypothesis being tested by Dr. Azar’s research group involves the number and types of molecular factors activated by PRK and LASEK.
“What we hypothesize is that there are distinct differences between epithelial proliferation and epithelial migration. In PRK, the epithelial cells have to do both, and the migratory cells express a number of biologically active proteins and growth factors that may lead to the haze formation”, Dr. Azar said. “ So if the epithelium is in place and the cells are proliferating but not migrating, the metabolic activity is different [and] the expression of the enzymes and proteins and growth factors are less. This may explain the reported differences in corneal haze after LASEK as compared with PRK."
And even Dr. Koch sees a few patients whom he believes will be LASEK candidates. "For instance, I had a patient the other day in whom small epithelial defects occurred after bilateral LASIK. In one eye the epithelium had to be removed. In the other, I was able to patch epithelium on top of the defect." The next day, he noticed that the patient had some diffuse lamellar keratitis in the unpatched eye.
"So in both eyes there was bare stroma, but the eye in which I was able to patch epithelium back over the defect healed better” he reported. "This leads me to think that there might be an implication that the epithelium plays a role in suppressing an inflammatory response in these patients."
ON TO SUPER-VISION
LASEK might eventually get a boost from the move toward customized ablations, added Dr. Durrie, because the deeper flap in LASIK causes unpredictable changes in the cornea. The epithelial thickness also may be less likely to change after LASEK, further improving the predictability for wave-front-guided ablations, Dr. Azar said.
This may be why, in the Alcon LadarVision studies of Custom Cornea, the patients with PRK had better results than did those patients in the LASIK group.
"In the customized cornea studies, we're finding that when you do a LASIK flap it induces some biomechanical destablization of the cornea," Dr. Durrie said. "You get spherical aberration, or coma. So if we're looking for the ultimate 'super vision,' a lot of us are beginning to think that we're going to have to get rid of the stromal flap to do it."