Microkeratome considered predictable, reliable unit

The MK-2000 microkeratome (Nidek) is able to produce thin flaps reliably and safely with a very low complication rate, said Arturo S. Chayet, MD, a refractive surgeon with the Codet-Aris Vision Institute, Tijuana, Mexico.

Dr. Chayet used the MK-2000 to perform LASIK on a series of eyes as part of a comparison study of six microkeratome models conducted by the Flap Thickness Study Group. Results of that study were published in May 2004 in the Journal of Cataract and Refractive Surgery.

"In this study, the MK-2000 was among the microkeratomes that performed the best in terms of flap thickness and reproducibility," he explained. The MK-2000 also had a low rate of complications, with minor events occurring in only 0.05% of cases.

The MK-2000, with the 145-µm and 130-µm heads, produced the two lowest mean flap thickness rates among the keratomes included in the study. With the 130-µm blade head, the mean flap thickness was 110.7µm (SD ±19.3µm). The 95% range was 65.3 to 153.7µm. In procedures performed with the 145-µm blade head, the mean flap thickness was 103.1µm (SD ±14.5µm) and a 95% range of 66.6 to 137.0µm. In contrast, the highest mean flap thickness in the study was 197.7µm.

The ideal flap thickness These results were very good, said Dr. Chayet, who described himself as one of the early advocates of very thin flaps. For him, the ideal flap thickness should be between 100 and 120µm, and the mean flap thickness in his study was within that range for both blade heads used with the MK-2000. He added that he uses the MK-2000 keratome for most of the LASIK procedures he performs.

Advantages of a thin flap include better cornea biomechanical strength and quicker visual rehabilitation with less flap edema, Dr. Chayet said. He cautioned, however, that results may vary with the MK-2000 or with any other microkeratome because of variations in the blade manufacturing process.

Besides reproducibility of thin flaps, other advantages of the MK-2000 include three ring size selections, 8.5, 9, and 9.5 mm, which make it adaptable for performing procedures on patients with myopia, hyperopia, or astigmatism, Dr. Chayet added.

The keratome also features a 19-mm suction ring that fits well into small eyes, which is particularly important in procedures performed on Asian patients. In addition, tonometry can be performed before cutting begins. The MK-2000 is also designed to prevent obstruction from lids and lashes; there are no gears, guides, or external stoppers that could cause jamming during cutting.

Overall the flap thickness study was a multicenter, prospective trial that involved 18 surgeons who performed LASIK on the eyes of 1,061 consecutive patients. A total of 1,634 eyes were reviewed.

Age, sex, surgical order, keratometry, white-to-white measurement, laser used, plate thickness, head serial number, blade lot number, and occurrence of epithelial defects were recorded.

Intraoperative pachymetry was obtained before the microkeratome was placed on the eye, while residual bed pachymetry was measured after the cut had been created and the flap lifted.

Charles Moore, MD, who is in private practice at the International EyeCare Laser Center in Houston, has used Nidek microkeratomes for several years, performing LASIK on more than 2,000 eyes with the MK-2000. He has not been involved in clinical trials of the MK-2000 but praised it as "the best kept secret in ophthalmology."

"It is a wonderful microkeratome, and it is very reproducible and safe. It can create flaps of a predetermined thickness in a safe way with a minimal amount of side effects and complications," Dr. Moore said.