Microkeratome associated with low rate of complications, good UCVA

July 15, 2007

In eyes undergoing LASIK, use of one proprietary microkeratome (Zyoptix XP, Bausch & Lomb) yields a low rate of complications, good uncorrected visual acuity, and refractive precision in a review by two surgeons in the same practice.

Key Points

"There is a raging debate in the ophthalmology community as to whether there is a clear-cut advantage to using a mechanical microkeratome or . . . a femtosecond laser [to create a] flap," said Dr. Anderson, associate clinical professor, Department of Ophthalmology, University of Wisconsin, Madison, and in private practice in Madison.

"There is a definite logistical and cost advantage to using a mechanical microkeratome.

To add to the body of information on this topic, Dr. Anderson and co-author Michael B. Shapiro, MD, evaluated 1,259 consecutive cases performed when the authors switched from one microkeratome (Hansatome, Bausch & Lomb) to another (Zyoptix XP) and included the patients treated during the learning curve with the new instrument, Dr. Anderson explained.

One difference discovered between the two microkeratomes is that one (Zyoptix XP) has internal gears and can be switched from left to right without having to disassemble the instrument, which can induce other possible errors in the procedure, Dr. Anderson explained.

This microkeratome also has a zero-compression head to reduce epithelial defects, standard 8.5- and 9.5-mm suction rings, as well as interchangeable parts.Another difference is that flap orientation can be changed between horizontal and vertical, tighter blade tolerances. In addition, the motor sleeve is sterilized, he said.

In their study, Drs. Anderson and Shapiro created superior hinges. Either the 120- or 140-µm plate was used, and either the 8.5- or 9.5-mm suction rings were used depending on the keratometry readings, Dr. Anderson said. In patients with small eyes or keratometry readings greater than 46, the 8.5-mm suction ring was used. A standard flap thickness was performed on 100 eyes using only the 140-µm head.

All patients underwent conventional ultrasound and pachymetry, and the bed thickness was measured intraoperatively, he said.

"The average flap thickness was 133 µm, with a range of 119 to 141 µm," Dr. Anderson said. "We were very satisfied with this tightness, with the fact that there were very few thick flaps that might have created difficulties with how much laser to apply to keep the bed thickness a minimum of 270 µm."

He also commented on an optical coherence tomography study in which Drs. Neuhann and Lege found no significant difference in the standard deviation of flap thickness between flaps created with a femtosecond laser and those created with this microkeratome (Zyoptix XP).

In six patients treated with the microkeratome, corneal abrasions and substantial epithelial shifts were seen, for an incidence of 0.5%. Substantial flap-making complications occurred in three cases, for an incidence of 0.2%; one case had a buttonhole flap, and two cases had partially cut flaps.

The buttonhole flap occurred in the second eye of the patient who was treated; no complications had occurred in the second eye. The cause of the buttonhole flap could not be determined; a new flap was cut 3 months later without a loss of best-corrected visual acuity.

One of the partially cut flaps occurred in the case of a patient with severe blepharospasm; no clear cause was determined in the second case. Flaps in both patients were re-cut, and the results were excellent, according to Dr. Anderson.

"For us, the microkeratome provided excellent performance," he said. "The instrument had an excellent safety profile, and the precision has been very good.

"In addressing the debate over the superiority of a mechanical microkeratome and the femtosecond laser, surgeons will have to look to their own preferences to rationalize their choices," Dr. Anderson concluded. "In our practice, we are currently satisfied with the [Zyoptix XP] microkeratome."