PURPOSE: To evaluate the incidence of epithelial defects in patients who have had laser in situ keratomileusis (LASIK) surgery with the standard compression Hansatome microkeratome head in comparison to the modified (zero-compression) Hansatome microkeratome head (Bausch & Lomb, Rochester, NY). METHODS: This study was a retrospective review of 404 consecutive patients who had LASIK surgery on both eyes between January 2002 and June 2002. The standard compression microkeratome head was used in 216 (53%) cases and the zero-compression microkeratome head was used in 188 (47%) cases. Epithelial defects were categorized as loose epithelium, or a break in the epithelium, within the area of the flap. An adverse outcome for a patient was defined as having an epithelial defect in at least one eye. Odds ratios were estimated using logistic regression. RESULTS: When the standard compression microkeratome head was used, 19 (8.8%) patients had an epithelial defect in at least 1 eye. When the zero-compression microkeratome head was used, 5 (2.7%) patients had an epithelial defect in at least 1 eye. Logistic regression comparing the risk of epithelial defect in either eye with the standard compression head versus the zero-compression head resulted in an age-adjusted odds ratio of 0.2 (95% confidence interval, 0.07 to 0.58, P<.05). CONCLUSIONS: These findings provide evidence that LASIK surgery with a zero-compression head reduces the risk of epithelial defect compared to the standard compression head of the Hansatome microkeratome.