Flap thickness accuracy: Comparison of 6 microkeratome models

Purpose: To determine the flap thickness accuracy of 6 microkeratome models and determine factors that might affect flap thickness. Setting. Magill Research Center for Vision Correction, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, USA. Methods. This multicenter prospective study involved 18 surgeons. Six microkeratomes were evaluated: AMO Amadeus, Bausch & Lomb Hansatome(R), Moria Carriazo-Barraquer, Moria M2, Nidek MK2000, and Alcon Summit Krumeich-Barraquer. Eyes of 1061 consecutive patients who had laser in situ keratomileusis were included. Age, sex, surgical order (first or second cut), keratometry (flattest, steepest, and mean), 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 just before the microkeratome was placed on the eye. Residual bed pachymetry was measured after the microkeratome cut had been created and the flap lifted. The estimated flap thickness was determined by subtraction (ie, mean preoperative pachymetry measurement minus mean residual bed pachymetry). Results: A total of 1634 eyes were reviewed. Sex distribution was 54.3% women and 45.7% men, and the mean age was 39.4 years +/-10.6 (SD). In addition, 54.5% of the procedures were in first eyes and 45.5%, in second eyes. The mean preoperative pachymetry measurement was 547+/-34 mum. The mean keratometry was 43.6+/-1.6 diopters (D) in the flattest axis and 44.6+/-11.5 D in the steepest axis. The mean white-to-white measurement was 11.7+/-0.4 mm. The mean flap thickness created by the devices varied between head designs, and microkeratome heads had significant differences (P<.05). Factors that explained 78.4% of the variability included microkeratome model, plate thickness, mean preoperative pachymetry, K-min, surgery order, head serial number, blade lot number, and surgeon. Factors such as age, sex, K-max, K-average, white to white, and laser had no significant correlation to flap thickness. Conclusions: The results demonstrated variability between the 6 microkeratome models. Device labeling did not necessarily represent the mean flap thickness obtained, nor was it uniform or consistent. Thinner corneas were associated with thinner flaps and thicker corneas with thicker flaps. In addition, first cuts were generally associated with thicker flaps when compared to second cuts in bilateral procedures.