A discussion of LASIK is never complete without addressing possible flap complications from a mechanical microkeratome. Yet according to a growing number of ophthalmologists, buttonhole flaps and epithelial defects are not the only problems associated with LASIK flaps: This step of the refractive surgery process may be getting in the way of perfection as well.
“Every time you cut a flap—whether it is with a laser or a conventional microkeratome—you induce more aberrations,” said Richard W. Yee, MD, professor and chairman of ophthalmology at the University of Texas Health Science Center, Houston. “With wavefront-guided customized ablation, this is of concern since the objective is to correct aberrations, not induce more.”
In search of an answer, some ophthalmologists have shifted away from flaps and toward advanced surface ablation (ASA),1 which covers all forms of nonlamellar refractive procedures such as laser subepithelial keratomileusis (LASEK) and “advanced” PRK.
Closing the Gap
“While the results from wavefront using the traditional flap are impressive, results from wavefront combined with surface ablation are even better, [as] this approach does not induce aberrations,” said Marguerite B. McDonald, MD, clinical professor of ophthalmology at Tulane University, New Orleans. “Combine this factor with its safety—no DLK [diffuse lamellar keratitis] or epithelial ingrowth—and you can see why more clinicians are returning to the surface.”
However, for patients, “returning to the surface” may also represent more pain and a longer recovery time when compared with LASIK. Dr. McDonald countered that with recent breakthroughs in pain control (such as bandage lenses and comfort drops), pain is less of a problem, and many patients are willing to tolerate a slightly slower vision recovery in exchange for what many believe is a safer procedure.
Thus, the gap between LASIK and ASA is closing, opening the door to an increased acceptance of techniques that do not require the formation of a lamellar corneal stromal flap using a mechanical or laser microkeratome.
Advanced PRK. Advanced techniques are what differentiate the PRK of the 1990s from that practiced today. Dr. Yee pointed out that newer-generation excimer laser technology, smaller spot beams, high-fidelity laser tracking systems, smoother central surfaces and peripheral transition zones, and smoothing techniques offer improved healing, less secondary scarring, less haze, fewer aberrations and superior outcomes than with early PRK surgery.
LASEK. This differs from PRK in that the epithelial flap is placed back on the stroma after laser ablation. Massimo Camellin, MD, in Rovigo, Italy, introduced LASEK in 1998. Today, he uses a 20 percent alcohol solution applied to the epithelium for an average of 20 seconds, then removes it with a Weck-cell sponge. The alcohol solution weakens the epithelial attachment to Bowman’s membrane, allowing the removal of a continuous layer of tissue. Dr. Camellin continues to be enthusiastic about LASEK. “LASEK is the best choice for customized ablation because it allows a better relationship between the analysis of the cornea and the shape of the treatment,” he said. Additionally, he has observed only “slight and rare haze problems” and excellent results in the more than 1,000 procedures he has performed in the past 5 1/2 years.
Dr. Yee is also a fan of using alcohol to create the flap. “When first described, the epidetachment solution consisted of ethanol and sterile water,” he said. “However, I now recommend the use of balanced salt solution and alcohol, which seems to be less toxic to the epithelium.” The solution is left in place from 30 to 70 seconds, depending on the patient’s age, history of contact lens wear, ethnicity and signs or history of any trauma or previous corneal surgery.
One of the major issues with LASEK is haze formation—the result, Dr. Yee speculated, of excessive exposure to alcohol and resultant epithelial cell death. To counter this, Dr. Yee’s postoperative steroid regimen is a 0.1 percent dexamethasone solution used six times daily for two to four weeks based on the rapidity of epithelial healing and haze formation. When excessive haze formation is present, dexamethasone may be administered hourly. In addition, the use of autologous serus helps epithelial healing and is effective in reducing haze.
Epi-LASIK. Thomas V. Claringbold II, DO, chief ophthalmologist of Mid-Michigan Physicians Group in Clare, Mich., is an advocate of epi-LASIK, a new procedure that he first performed last fall. In this approach, an automated device passes a blunt oscillating blade over the corneal surface while suction is applied. This creates a hinged sheet of epithelium. It is reflected out of the way and the cornea is resculpted with the laser. The epithelial sheet is then replaced on the surface of the eye and a bandage contact lens is inserted for a few days. No alcohol is used in this approach.
Epi-LASIK appears to help reduce corneal haze and promote comfort following the procedure, said Dr. Claringbold. The procedure “may provide a quicker recovery time [three days in contrast to four], and these initial patients seemed to function a bit better during the first week following surgery,” he said. “This is a terrific alternative for patients with thin corneas.”
However, no one in the United States is performing epi-LASIK on a routine basis at this time. “The epi-LASIK device is currently being perfected and is therefore not even available as a demo at the moment,” said Dr. McDonald.
Several ophthalmologists are refining alternative versions of LASEK:
Gel-assisted. Dr. McDonald has been searching for an alternative that allows for the stripping out of the epithelium without denaturing it by exposure to alcohol. She thinks she has found the answer in GenTeal gel.
“At the beginning of the LASEK procedure, I make a tiny linear abrasion parallel to the limbus about 1 millimeter in length,” she explained. “Next, I apply 10 drops of sodium chloride 5 percent—at the rate of one drop per second—over the entire cornea, which stiffens and loosens the epithelial cells without killing them. Then, I irrigate the solution away.”
Dr. McDonald places the microkeratome suction ring onto the limbus, centered over the cornea. She warned that the suction should only be used for 30 seconds and then only repeated once if necessary. While the eye is hard from the suction, she uses a LASEK spatula to slip through the small epithelial abrasion.
“The only way to deal with the epithelium now is to squeeze the GenTeal gel through the little linear abrasion, because the epithelium has not been stiffened or killed by alcohol,” she added. She uses the gel to gently push or manipulate epithelium away from Bowman’s layer.
“This approach works brilliantly on individuals between ages 40 and 45 and above. However, below age 40, you don’t get a complete epithelial sheet, which is an issue,” she said.
“Results from a prospective randomized trial we conducted comparing gel-assisted LASEK vs. classic alcohol-assisted LASEK showed strong trends in favor of the gel technique, but we saw no statistically significant difference between the two approaches, perhaps because we couldn’t strip the epithelial in a consistent sheet in the younger patients.”
Hydroviscodissection. Richard C. Rashid, MD, of the Eye Physicians and Surgeons Corporation and the West Virginia Laser Eye Center, South Charleston, introduced BSS hydrodissection and GenTeal viscodissection to elevate the flap. He noted that the keys to successful “fluidic dissection” are a loosened epithelium, especially at the more adherent edge, and a proper cannula with the port placed under the flap before fluid delivery. Techniques to loosen the epithelium and decrease alcohol application before hydroviscodissection are Xylocaine Gel 2 percent applied 15 to 30 minutes preoperatively and suction epithelial detachment. The latter is accomplished by applying a contact lens suction device or the Rashid LASEK sponge in a rotating motion.
“Hydroviscodissection makes flap retraction easier and less traumatic,” Dr. Rashid said, “and it decreases corneal and conjunctival drying. It decreases alcohol application time and sometimes can be done without alcohol.” Moreover, he said, hydroviscodissection does not require a “$50,000 instrument” but rather is a safe, economical approach that is adaptable to any LASEK technique, requiring only BSS or GenTeal, a syringe and a Rhein-Rashid front port or other appropriate cannulae.
1 A term coined by a committee at the First International LASEK Congress in Houston, 2001. For information on the upcoming Third International LASEK Congress, check www.lasekcongress.com.
Drs. Camellin, Claringbold, McDonald, Rashid and Yee have no financial interests related to products mentioned in this article.