Study: Moria microkeratome resistant to intraoperative flap complications

There were no major flap complications using the Moria C-B microkeratome. Long-term visual outcomes appeared to be unaffected.

BOSTON — Conventional microkeratomes, regardless of whether they are automatic or manual, have become the standard flap maker of choice for most surgeons. The common reasoning is because the conventional microkeratome does not have the suspected disadvantages of pinching the epithelium during the cut, like other microkeratomes are widely thought of as doing.

During the American Society of Cataract and Refractive Surgery 2000 meeting Keith A. Walter, MD, showed his results using the Moria Carriazo-Barraquer (C-B) (Doylestown, Pa.) rotational microkeratome.

“Just to give you a little background, the first microkeratomes were motorized translational and always created a nasal hinge. They were developed specifically for automated lamellar keratoplasty (ALK) and not specifically for laser in situ keratomileusis (LASIK). So, they had problems with incomplete flaps at times, buttonhole flaps and free flaps, and it was possible for anterior chamber perforation,” Dr. Walter said.

On the other hand, the Carriazo-Barraquer microkeratome has a rotational design, he said. It can be automated or use a manual gas-driven turbine. The rings can be varied to accommodate different sized corneas. Additionally, the flap hinge location may be varied.

In Dr. Walter’s opinion, the rotational microkeratomes appear to be safer than translational microkeratomes. He referred to previous papers on the subject and also Dan Durrie, MD’s, data of approximately 5,000 consecutive cases where he had no major flap complications with the Hansatome (Bausch & Lomb Surgical).

Dr. Walter said he believes one of the reasons surgeons need to get used to the rotational microkeratomes is because of the friction in shearing forces. He said he believes they generate epithelial trauma.

“We have defined epithelial sliders for this study as areas of stretched, but intact, epithelium that have lost their firm attachment to Bowman’s layer. So, they are not true defects. Sliders are commonly encountered in the use of rotational microkeratomes, but their etiology and significance are poorly understood,” Dr. Walter said.

Sliders versus non-sliders

The purpose of Dr. Walter’s study was to identify all of the intraoperative complications with the Moria C-B, to investigate the incidence and severity of epithelial sliders, to investigate the suspected risk factors for these sliders and to determine their effects on the final visual outcome.

Dr. Walter’s study was a retrospective chart review of the first 331 consecutive eyes that underwent LASIK by a single surgeon. All of these eyes were done with the manual turbine Moria C-B, and the study reported all intraoperative events. The presence or absence of sliders was identified. Their location, size and numbers of sliders were identified. And the study included the variables of age, sex, contact lens history, abrasion history, Ks, ring size, smoking status and pachymetry values.

To further define the location of these sliders, Dr. Walter used the Visx (Santa Clara, Calif.) reticule, where zone 1 was defined as the central 4 mm, zone 2 was the millimeter ring around that and zone 3 was the peripheral part of the flap. The study results showed no free flaps, no incomplete flaps, no buttonholes and no anterior chamber perforations. “We did lose suction on one eye using the H-ring on a patient with a 13.5-mm cornea that resulted in a 1- × 3-mm flap where the hinge was not anywhere near the pupil or visual axis,” Dr. Walter said.

There was evidence of slider formation in 33 of 331 eyes or approximately 10%. Sliders that were greater than 2 mm in size appeared in 13 of these eyes, or 4%, and five eyes had sliders in that central 4 mm, 1.5%. Looking at the presumed risk factors for sliders, the slider group that had 33 eyes was age 54 on average, and the non-slider group was 43. Using multi-variant analysis revealed that age was the only significant risk factor for slider formation.

No major acuity loss

As far as visual outcomes on day 1, the slider group did not fair as well as the non-slider group. The percentage of patients who were 20/40 or better in the slider group was only 55%, but it was 90% in the non-slider group. By 2 weeks, the two groups were similar, with a slight edge to the non-slider group.

As far as the slider group and their visual outcome, no eyes lost more than one line of best-corrected visual acuity at the last visit. Only five eyes lost one line of best-corrected visual acuity, and three of these eyes were eyes that involved the central 4 mm. The mean return of best-corrected visual acuity for these five eyes was 77 days.

Dr. Walter also showed the rates of sliders by month. “When we first got our Carriazo-Barraquer about a year ago (May 1999), during the first quarter, a large number of these sliders went unreported because they were unrecognized. But as soon as we realized that there was a problem, during October, November and December, our rate went up because we were reporting all sliders, no matter what size they were.

“Then, in December, we started, on the back pass, going off suction. With the Carriazo, you can function or operate the motor independent from the suction. So, you can come off the motor well before you come off suction or vice versa. So we would come off suction, and we seemed to decrease the rate of our slider formation, having less than 5% in the past few months,” Dr. Walter said.

“We do lubricate prior to the microkeratome pass. Now, if I see a slider, I manage it by trying to fix it before I lift the flap back up. I put it in its approximate position, lift the flap up and do the ablation. And now, when I put the flap back down, if it’s a non-slider patient, I’ll let the flap dry for 30 seconds to a minute. But, if I see a slider there, I’ll play with it and get it to smooth out. If you wait long enough, maybe 5 minutes sometimes, that epithelium will retract back down into a better position. And they seem to do a lot better as far as visual outcome,” Dr. Walter said.

According to the study, there were no major flap complications using the Moria C-B microkeratome. The incidence of the sliders, about 1% to 2%, and the epithelial disturbances appeared to slow the visual recovery after LASIK. Dr. Walter said that long-term visual outcomes appeared to be unaffected, and age was the only determined risk factor. With experience and proper management of the keratome, slider incidence may decrease, he said.

Lubrication and management factors

After Dr. Walter’s presentation, several of the members of the panel who observed the presentation remarked about their successes with different lubricants and management of the microkeratome.

Roger F. Steinert, MD, explained that, “Because of epithelial defects, we have both the Hansatome and the Moria C-B, and because of our difficulty with epithelial defects with both, we took a deep breath and started using Refresh Plus (carboxymethylcellulose sodium, Allergan) routinely on 100% of the cases immediately before passing the microkeratome. Although we haven’t solved the problem, we definitely have a lower incidence of epithelial defects, and we’ve had no problem with the mechanism getting crusted or jammed or anything like that.”

Stephen G. Slade, MD, said, “We’ve had good luck just using proparacaine hydrocholride (Bausch & Lomb; St. Louis), because it does contain glycerin. As far as using viscous materials, such as artificial tears, I think that’s probably fine, but I would be cautious about getting it under the flap on the interface.”

“We have switched to using some artificial tear preparations, as well. We have wrestled with the difficulty of epithelial defects, because as we’ve gotten better with microkeratomes, we don’t have free caps, small caps and thick and thin caps or buttonholes so much anymore. Epithelial defects have become the most common and most difficult problem that we have to deal with in this population. We became concerned about these about 3 or 4 months ago and instituted a new protocol for recording epithelial defects. So, we started recording even very small epithelial defects at the time of surgery,” R. Doyle Stulting, MD, said.

He explained that his practice has four Hansatomes, and he discovered that the epithelial defect rate among the four was quite different. Looking at the way the microkeratomes worked, he noticed that the flap in the Hansatome gets reflected almost 180° back as the microkeratome advances. Dr. Stulting looked at the finish on the microkeratomes and the area where the flap has an opportunity to go to see if that had an effect.

“Doug Mastel happened to come by our center one day, and we talked with him a little bit about it. He took one of the microkeratomes and refinished that entire area. When he brought it back, we did another series, so that we had about 200 eyes before and after refinishing. The three microkeratomes that were not refinished had exactly the same epithelial defect rates. They ranged from 5% to 14%. The one that went for refinishing went from 11% to 3%, which was statistically significant at the 0.001 level,” Dr. Stulting said.

He concluded that the most important contribution to epithelial defects, in regard to the Hansatome, is the finish and the characteristics of the plate. He recommended that if surgeons find they have high epithelial defect rates with particular Hansatomes, they should take a look at that and probably have it refinished.

For Your Information:

• Keith A. Walter, MD, can be reached at 1 Medical Center Blvd., Winston-Salem, NC 27157; (336) 716-4091; fax: (336) 716-7994; e-mail: dwalter@wfubmc.edu. Dr. Walter does not have a direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any company mentioned.
• Roger F. Steinert, MD, can be reached at 50 Staniford St., Ste. 600, Boston, MA 02114; (617) 367-4800; fax: (617) 573-4912; e-mail: rfsteinert@eyeboston.com.
• Stephen G. Slade, MD, can be reached at 3900 Essex Lane, Ste. 101, Houston, TX 77027; (713) 626-5544; fax: (713) 626-7744. Dr. Slade does not have a direct financial interest in any product mentioned in this article, nor is he a paid consultant for any company mentioned in this article.
• R. Doyle Stulting, MD, can be reached at 875 Johnson Ferry Rd., Ste. 310, Atlanta, GA 30342; (404) 778-3863; fax: (404) 778-5128; e-mail: ophtrds@emory.com.