Comparative performance of the Zyoptix XP and Hansatome zero-compression microkeratomes

PURPOSE: To compare flap parameters produced by the Zyoptix XP and Hansatome microkeratomes (both Bausch & Lomb) and to evaluate preoperative variables contributing to flap thickness variation. SETTING: Private practice, St. Louis, Missouri, USA. METHODS: Flap dimensions in 75 eyes that prospectively had laser in situ keratomileusis using the Zyoptix XP microkeratome were compared with a historical control sample of 75 eyes treated with the Hansatome microkeratome. The 2 groups were matched for mean keratometry, central corneal pachymetry, spherical equivalent (SE), age, and microkeratome head size and suction ring diameter. RESULTS: The mean ultrasound-measured flap thickness was 126.54 mu m +/- 14.6 (SD) and 143.74 +/- 15.0 mu m for the 120 mu m and 140 mu m Zyoptix XP heads, respectively, and 128.90 +/- 20.4 mu m and 143.32 +/- 21.0 mu m for the 160 mu m and 180 mu m Hansatome heads, respectively. The standard deviation in flap thickness was smaller and statistically significant for the Zyoptix XP (+/- 14.8 mu m) versus the Hansatome (+/- 20.7 mu m) (P=.0039, F test). Preoperative pachymetry and SE (P<.001) accounted for 20% of the variability in measured flap thickness using the Hansatome. For the Zyoptix XP, preoperative pachymetry was statistically significant in explaining the variation in flap thickness with the 120 mu m head (P=.02) but not with the 140 mu m head. Variation in flap thickness from either Zyoptix XP head was not statistically related to the preoperative SE. CONCLUSION: Although the 2 microkeratomes produced flaps of similar mean thickness, the Zyoptix XP showed significantly less variation in flap thickness than the Hansatome, was less affected by measurable preoperative variables such as SE, and was closer to nominal labeling.