PURPOSE: To evaluate the effects of different flap shapes and hinge angles on opaque bubble layer (OBL) formation using a femtosecond laser for flap creation in LASIK surgery. METHODS: This retrospective study evaluated 138 eyes of73 patients who underwent femtosecond laserassisted LASIK with a 150-kHz IntraLase femtosecond laser (Abbott Medical Optics, Inc., Santa Ana, CA) for myopic astigmatism and compared differences between different fap shapes and hinge angles on OBL formation. The surgical procedures were videotaped, and the patterns and sizes of the OBLs seen during surgery were analyzed. Preoperative and postoperative data including patient demographics, refractive status, keratometry, central corneal thickness, and intraoperative data (flap size and pocket parameters) were recorded. The eyes were divided into four groups based on the corneal flap shape (elliptical versus round) and hinge angle (50° versus 60°). RESULTS: The preoperative demographic data, mean spherical errors, cylindrical power, and central corneal thickness were not significantly different among the groups. Of the 138 eyes, 107 (77%) developed an OBL covering a mean area of13.8% ± 12.6% in each case. This area was significantly smaller in the elliptical flap with 60° hinge angle group (P <.05). CONCLUSIONS: An oval-shaped flap with a larger hinge angle tended to result in less OBL formation in femtosecond laser-assisted LASIK.