Ninety-three consecutive patients undergoing bilateral wavefront-guided laser refractive surgery in the Department of Ophthalmology of the National Taiwan University Hospital between September 2004 and December 2007 were enrolled in this retrospective study. Before laser refractive surgery, all patients were seated in front of the Zyoptix 100 system platform (Bausch & Lomb, salt lake city, UT, USA) and received Zywave aberrometer measurement on both eyes. When patients were in the supine position for refractive surgery, an infrared camera mounted on the laser system (Technolas 217z100 excimer laser system, Bausch & Lomb)obtained iris images on undilated pupils before laser ablation. Overall cyclorotation was detected by a comparison between iris images of undilated pupils in the supine position and dilated pupils in the seated position before laser treatment. The degree and direction of position-induced cyclorotation were assessed.