LASIK—laser in situ keratomileusis—is performed with a microkeratome to create a thin flap of tissue about one-fourth the thickness of the cornea. The flap is lifted and the exposed surface is reshaped using an excimer laser. The flap is then repositioned over the cornea.
LASEK—laser-assisted subepithelial keratectomy, or laser epithelial keratomileusis—is accomplished with the use of an alcohol solution that loosens the epithelium and allows it to be separated from Bowman's layer intact. The excimer laser is used to complete an ablation similar to PRK, and the epithelium is repositioned over the ablated area. The patient wears a bandage contact lens for a few days after surgery. A microkeratome is not used, and no stromal lamellar cut is made.
PRK—photorefractive keratectomy—is a procedure involving the removal of the epithelium by gentle scraping or use of the excimer laser, and subsequent use of an excimer laser to reshape the stroma.IN THE BEGINNING
Approximately 3 years ago, on September 5, 1998, Massimo Camellin, MD, of Rovigo Micro Surgery in Rovigo, Italy, described the procedure known as LASEK. In the LASEK procedure, the surgeon uses a 270o trephine and alcohol to loosen the epithelium. The epithelial flap is “rolled off Bowman's layer,” the surgeon performs laser ablation, and repositions the epithelium on the wound. A bandage contact lens is used for a few days after surgery. Lee Shahinian, MD, Associate Clinical Professor at Stanford University, informs us that when Dr. Camellin coined the name, LASEK was an acronym for laser epithelial keratomileusis. The “E” is used to emphasize that this is an epithelial procedure. Since that original naming, a new terminology has been applied to the acronym. Although the acronym remains the same, Drs. Camellin and Shahinian now refer to the procedure as laser-assisted subepithelial keratectomy because it provides a more accurate description of the procedure.
Safety
Drs. Shahinian and Camellin affirm that LASEK inherently appears to be a safer procedure than LASIK because the stromal flap complications are eliminated. Dr. Camellin adds that a potential advantage of LASEK over PRK is that the raw stroma is not exposed to tear film and its products. He postulates that even the 3 to 5 days' exposure of the raw stroma to the tear film in PRK may be the root cause of haze formation, and replacement of the epithelial layer in LASEK adds a potential protective mechanism. Dr. Camellin has completely abandoned LASIK, stating that he covers all refractive errors better by performing LASEK.
Contraindications to LASIK
LASEK can be performed when LASIK is not recommended or is difficult to perform. As pointed out by Dr. Shahinian, these situations include patients with thin, steep, or flat corneas, high myopia with thin pachymetry, deep-set eyes, glaucoma, filtering blebs, and scleral buckles. Patients who have thin corneas and high prescriptions may not be treatable with LASIK because the amount of laser treatment would compromise the stability of the eye. However, with LASEK, there is an extra 100 microns available for treatment. “When performing LASIK, we can only correct -7 or -8 D in a normal cornea with a thickness of 530 mm. With LASEK, we can use the whole corneal thickness, so we can correct, without problems up to -13 D in almost all cases,” explains Dr. Camellin. Lee Nordan, MD, Director of the Laser Eye Medical Group in Carlsbad, CA, jumps in, “Although the surgeon can correct up to -13 D, the patient's quality of vision will be compromised because the functional optical zone is so small.” When correcting extremely high degrees of myopia, over -10 D, the surgeon is now treating close to the limit of any laser procedure and optimal results are not always attainable. Dan Durrie, MD, Associate Clinical Professor at the University of Kansas Medical Center and Director of Refractive Surgery at The Hunkeler Eye Centers in Overland Park, KS, adds that because LASEK doesn't cut across the corneal nerves, it may have less chance of causing dry eyes, which is why he performs LASEK on dry-eye patients.
It's All About the Epithelial Flap
A small tear or even a buttonhole in the epithelial flap is not a critical problem in LASEK, as a flap tear or buttonhole is in LASIK. Dr. Shahinian explains that if there is a tear in the epithelial flap, the surgeon can perform the ablation and put the epithelial flap back down; the epithelial flap defects are healed by the next day and have no impact on the result of the procedure. In addition, in LASEK, when the surgeon repositions the epithelium, the positioning is not critical—the epithelial flap can overlay the intact epithelium outside the epithelial trephination gutter. Anterior basement membrane-like changes after LASEK can be seen, but are rarely clinically or visually significant.
AN EVOLVING PROCEDURE
LASEK is an evolving procedure. Dr. Shahinian states that improved techniques are being developed to elevate the epithelial flap. He explains that there is partial devitalization when the alcohol applied to loosen the epithelium kills the near majority of the epithelial cells. “There is a good chance that future methods will avoid the use of alcohol and cause less damage to the epithelium,” he offers. To reposition the epithelium, Dr. Camellin uses two rounded spatulas to roll it down, and then presses over the soft contact lens with an applanator to let the epithelium adhere over the stroma.
PRK=LASEK?
Many surgeons assert that LASEK is essentially the same procedure as PRK. Dr. Shahinian points to two recently published, controlled studies that both found significantly less pain and haze in eyes treated with LASEK compared with PRK-treated eyes.1,2 However, he admits that more studies and longer follow-up are needed. Dr. Nordan states that LASEK is the same as PRK, and that the only difference between the two procedures is that in LASEK, the surgeon uses alcohol to loosen an epithelial sheet. “I don't mind the concept of LASEK except that the LASEK advocates are trying to make it sound like a whole new operation,” he says. Dr. Nordan feels that LASEK will achieve high-quality results, will be beneficial in treating patients with lower levels of myopia and hyperopia, and with the presence of the epithelium, patients may experience less haze than standard PRK. However, he says, “I don't believe that there is a lot of difference between a sheet of epithelium that's loose and then heals, or falls off and heals, or just removing the epithelium, and then it heals. To me, it's the same operation.”
Dr. Nordan routinely performs PRK for hyperopia, prefers LASIK for myopia patients, and does not perform LASEK at all. The problem with LASEK, he feels, is that using alcohol produces less-than-accurate results because it dries out the central cornea. Dr. Durrie currently practices LASEK, and agrees with Dr. Nordan about its similarity to PRK. “Some people try to make LASEK something it is not. It's just a better way to do PRK. Many patients prefer LASEK to LASIK, and they also like the fact that it is new.” LASEK also appeals to patients who are afraid of the microkeratome blade, and for some surgeons who may not like the idea of creating a flap, this is an alternate treatment method.
OBSTACLESSlower Visual Recovery
When performing LASEK, the surgeon works closer to the optical surface of the cornea than in LASIK. “The surface of the cornea is critical because it is an air-water interface and it is where 67% of the bending of the light in the cornea takes place,” notes Dr. Shahinian. He continues, “Any slight irregularities in that surface are going to cause an impact on vision.” By analogy, Dr. Shahinian compares scraping and cutting a finger. If a finger is sliced, there is often not much pain and it tends to heal well. Whereas, if a finger is scraped, there will be more discomfort because there are more nerve endings on the surface and there is more disruption of the surface while it heals. Two weeks after a finger is cut or scraped, it is difficult to discern the manner of injury as the site would be well healed in both cases. If the surgeon moves deeper in the cornea, away from the optical surface, to cut the flap and to perform the laser ablation, then the surface tissue is not disrupted at all. The smooth optical surface is left intact, and therefore, the vision recovers more quickly after LASIK. After LASEK, the patient's vision is usually blurry for about 4 to 10 days.
More Pain
Another drawback of LASEK is that some patients will feel pain, which can range from a slight foreign-body sensation to a fair amount of discomfort the first postoperative day. NSAID eye drops, ice packs, and oral analgesics are used to alleviate this pain. Dr. Shahinian has also found diluted topical anesthetics helpful on an investigational basis.
DITCH THE MICROKERATOME?
The key difference between LASEK and LASIK is the use of the microkeratome. Dr. Shahinian expresses, “The heart of the argument is: Should we keep using the microkeratome, can we improve it enough to justify using it, or are there always going to be a certain number of complications no matter what we do with the microkeratome?” Dr. Shahinian's feeling is that there will always be unavoidable intraoperative and postoperative problems related to the microkeratome. “In the future, we will no longer be using the microkeratome on a routine basis,” he predicts. For the past year and a half, Dr. Nordan has been using 0.02% mitomycin C at the end of PRK to avoid haze, which has worked well for him. He explains that if the surgeon does not want to perform LASIK, and does not like to use alcohol as in LASEK, this is an alternate approach.
WRAPPING IT UP
Dr. Shahinian, who is no longer performing LASIK, states that for any surgeon, there will always be a choice to be made, which is best left up to the surgeon instead of being dictated by a decision that “this is safer” or “this is better.” His feeling is that LASEK is a safer procedure than LASIK, which is important to him. Dr. Durrie conveys that the reason some patients are more interested in LASEK than LASIK is because LASEK does not make a cut in the cornea. Surgeons have not yet performed enough LASEK procedures to detect what areas need improvement. Right now, Dr. Durrie performs about 75% standard LASIK and 25% LASEK. “I think that LASIK will always have its indications and I like to increase the options for our patients,” he maintains. Dr. Durrie offers LASEK to the majority of his younger, more active patients. It seems LASIK still has its uses, and not all surgeons are tossing their microkeratomes into the retired-instrument closet just yet.
Lee Shahinian, MD, is Associate Clinical Professor and former Director of Refractive Surgery at Stanford University in Stanford, California. He limits his practive to corneal disease and refractive surgery. (650) 969-7733; shahinian@nova-vista.com
Dan S. Durrie, MD, is in private practice with the Hunkeler Eye Centers in Overland Park, Kansas, and is Clinical Assistant Professor of Ophthalmology at the Kansas University Medical Center. (913) 491-3737; ddurrie@novamed.com
Lee T. Nordan, MD, is the Director of the Nordan Laser Eye Medical Group in Carlsbad, California. (760) 930-9696; lasertn@aol.com
John F. Doane, MD, FACS, is in private practice with Discover Vision Centers in Kansas City, Missouri, and is Clinical Assistant Professor of the Department of Ophthalmology, Kansas University Medical Center. Dr. Doane has been an investigator with several FDA clinical trials for laser techniques. (816) 350-4539; jdoane@discovervision.com
Stephen G. Slade, MD, FACS, is the National Medical Director for TLC Laser Center in Houston, Texas. Dr. Slade is the lead investigator for many new technologies including laser microkeratomes. (713) 626-5544; sgs@tlchouston.com
1. Lee JB, Seong JG, Lee JH, et al: Comparison of laser epithelial keratomileusis and photorefractive keratectomy for low to moderate myopia. J Cataract Refract Surg 27:565-570, 2001
2. Shah S, Sebai Sarhan AR, Doyle SJ, et al: The epithelial flap for photoreactive keratectomy. Br J Ophthalmol 85:393-396, 2001
