Thin head and single use microkeratomes reduce epithelial defects during LASIK. 
To evaluate the effect of microkeratome design and head dimension (flap thickness) on the rate of epithelial defects.  A retrospective review of 4000 LASIK procedures performed between May 2000 and December 2003 was conducted.  Intraoperative epithelial defects were identified in 326 cases.  The microkeratome design (reusable vs disposable) and head dimensions (100, 130, and 150 micron) were recorded along with age, sex, central ultrasonic pachymetry, keratometry, preoperative refraction (sphere, cylinder, and axis), and Schirmer testing.  The chi-square and Student t test were used in data analysis.  A total of 326 (8.2%) procedures had an associated epithelial defect.  With the reusable microkeratome, heads that produced thinner flaps were associated with a lower incidence of epithelial defects (P<.05 for all three groups, 100, 130 and 150 micron head).  When compared to a reusable head of the same dimension and to the entire population of reusable heads, the disposable 130 head exhibited a significantly lower rate of epithelial defects (P<.0001).  The results of this study support that both microkeratome design and head dimension (and resulting corneal flap thickness) play a role in the formation of epithelial defects.  These are surgeon selectable factors, unrelated to technique or patient risk factors, which can be used to reduce the rate of epithelial defects and associated complications.