A comparative study between the Schwind and Zyoptix XP microkeratomes

Maria Cecilia P. Garcia, MD, Joanne A. Barleta, MD, Gladness HA Martinez, MD, Robert Edward T. Ang, MD

To compare the flap thickness created by two different microkeratomes and its effect on visual outcomes.

This prospective study involved 32 eyes of 16 patients who underwent laser in situ keratomileusis (LASIK). Flap creation was randomly assigned to either the Schwind (110 µm) or Zyoptix XP (120 µm) microkeratome. Flap thickness was measured using the subtraction technique. Uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), low-contrast sensitivity, and aberrometry measurements were compared preoperatively and at 6 months postoperatively.

The mean flap thickness was 97 ± 13 µm (range, 81 to 116 µm) and 146 ± 27 µm (range, 71 to 181 µm) using the Schwind and XP respectively. The mean deviation from the labeled predicted thickness was –13 ± 13 µm and 26 ± 27 µm respectively, and this difference was statistically significant (p = 0.002). Three eyes had flap displacement, 1 had loose epithelium, and 1 had flap striae in the Schwind group. There were no complications in the XP group. At 6 months, 71% of eyes had UCVA of 20/20 or better in both groups. All eyes attained BCVA of 20/30 or better with spherical equivalent within ±1D of targeted emmetropia in both groups. Low-contrast sensitivity scores were higher in the Schwind group in most frequencies; however, the differences were not statistically significant. The mean change in the total higher-order aberration (HOA), trefoil, coma, quatrefoil was comparable between the groups. The mean change in spherical aberration was smaller (p = 0.03) in the Schwind (0.12 ± 0.35) than in the XP group (0.96 ± 1.3).

Flap thickness was more predictable with the Schwind than the XP. Schwind flaps were thinner, which may have resulted in more flap complications. Vision and refractive results were similar for both groups. There was no statistically significant difference in HOA; however, spherical aberration was significantly lower in the Schwind.

Keywords: LASIK, Schwind Carriazo, Zyoptix XP, Microkeratome, Flap thickness