Thinner flaps yield fewer epithelial defects in study

Use of a disposable microkeratome also helped reduce epithelial defects.

ByDavid Schonfeld

SLINGERLANDS, U.S.A. — Thinner LASIK flaps were associated with fewer epithelial defects in a study of 1,200 eyes here. Making thinner flaps may help lower the rate of epithelial abnormalities following LASIK, said Michael W. Belin, MD, FACS.

“Over the past 2 years, we’ve been concerned about the incidence of epithelial defects during LASIK,” Dr. Belin said. “Mainly, when patients come in for LASIK, they are assuming that it is a zero-risk procedure with an immediate return to vision and immediate healing response. While that’s true in the majority of patients, we find that if we get an epithelial defect, particularly if it’s a substantial defect, then the postoperative course is prolonged and the return of visual acuity is delayed.”

According to Dr. Belin, the Moria One disposable microkeratome has demonstrated better results than similar reusable keratomes in terms of epithelial abnormalities.

Thinner flaps

“We’ve been looking at factors as they relate to the incidence of epithelial defects,” he said. “Last year we presented our work on different flap thicknesses using the reusable Moria LSK One. What we found to a high degree of statistical significance is that as we went to thinner flaps, the incidence of any epithelial irregularity went down. One of the nice features of the Moria, as opposed to other microkeratomes, is that the flap thicknesses tend to be more reproducible with a tighter standard deviation. So when you think you’re getting 160 µm, you’re at least getting close to 160, ± 10 to 12 µm.”

Contrary to previous belief, a thicker flap may increase the potential for epithelial defects.

“We had three different flap thicknesses; a 180, a 160 and a 130, and what we found is that we have by far the highest incidence of epithelial defects with the 180 µm flap, which is a 150 head. A 150 head on the Moria produces a 180 µm flap. We had fewer incidents of epithelial abnormalities with the 160 µm flap, which is the 130 head and far, far fewer with the 100 head, which produces a 130 µm flap,” Dr. Belin said.

In a study involving 1,200 eyes, he said he found that the larger the flap thickness, the more incidence of epithelial defects.

“We found we had an incidence of epithelial abnormality with the 150 head of 13.2%, which is high,” he said. “With the 130 head it was 8.9% and with the 100 head it was zero. Additionally, we also found that in older patients there is an increased incidence of defects and thicker corneas, both of which were significant to a P-value of .001. The average age of the patient who had a defect was 46 versus 39 for the patient with no defect. The average preoperative pachymetry of the defects were 561 versus 550.

“However, we also compared whether these were all independent variables, and they were. So it isn’t just that older patients tend to have thicker corneas and they get thicker flaps; these are all independent variables.”

Disposable microkeratome

According to Dr. Belin, the Moria One disposable microkeratome offers many advantages.

“The disposable microkeratome has advantages for a high-volume surgeon. First, obviously, there’s no cleaning of the microkeratome. The turnaround time is significantly reduced,” he said.

“Additionally, there’s a slight difference in the design, not of the microkeratome head but of the vacuum ring. The disposable vacuum ring has two vacuum ports, 180° apart, as opposed to one vacuum port on the nondisposable. Additionally, on the disposable, the handle is held nasally, 180° away from the direction of travel of the microkeratome head as opposed to superiorly, which is 90° away.”

In a study comparing the disposable to the reusable microkeratome, Dr. Belin said he found the results with the Moria One to be superior.

“We did a retrospective review of 1,865 eyes on 952 consecutive patients,” he said. “We looked at the incidence of epithelial defects with the 100, the 130, the 150 and the disposable. It should be noted that disposable is the equivalent of a 130 head. Of those eyes, 44.1% were men and 55.9% were women. We found that the incidence of epithelial abnormality with the reusable 130 head was 11.8%. This is a much larger population than we originally reported. But the incidence with the disposable, using the same flap thickness, was 2.5%. Highly significant to P < 0.01.”

The disposable unit, which is plastic, demonstrated not only time-saving advantages but advantages in and after surgery as well.

“While people have talked about the disposable microkeratomes offering certain advantages such as improved turnaround time and complete sterility because they are not being used between patients, little has been reported about its surgical performance,” he said.

“When compared with equal head thickness, prefacing an equal flap thickness the disposable Moria had a highly significant decrease in the incidence of epithelial defects when compared to the reusable.”

According to Dr. Belin, the study is significant because it represents a new way to look at microkeratomes.

“One of the most interesting things is comparing epithelial abnormalities between different microkeratomes,” he said. “If you have one microkeratome that produces a 160 µm flap and you have another microkeratome you think is doing 160 µm but is really doing 130 µm, then you may have a lower incidence of epithelial defects on the one that’s producing the thinner flap. You may conclude it’s the better microkeratome, though it’s just producing a thinner flap.

“If you’re going to do comparisons between microkeratomes, then you have to test flap thickness. You have to make sure you’re comparing apples and apples. We purposely kept the microkeratome constant to determine microkeratome thickness, and this changed our practice totally.

“We used to make as thick a flap as possible, assuming that a thick flap is more stable. At this point, we’ve started going toward a thinner flap, we’ve completely switched to disposable microkeratomes when available, and our incidence of epithelial defect is almost zero.”

For Your Information:

Michael W. Belin, MD, FACS, can be reached at Cornea Consultants of Albany, 1240 New Scotland Rd., Slingerlands, NY 12159 U.S.A.; +(1) 518-475-1515; fax: +(1) 518-475-0645. Dr. Belin has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

Moria Inc. can be reached at 1050 Cross Keys Drive, Doylestown, PA 18901 U.S.A.; +(1) 215-230-7662; fax: +(1) 215-230-7670; e-mail: moriausa@moriausa.com; Web site: www.moria-surgical.com.