Patients were recruited from November 2016 to December 2017. All patients underwent a baseline preoperative assessment including anterior and posterior segment examinations. Inclusion criteria were: corneal thickness of more than 500 μm, manifest refractive sphere of -3.00 to -6.00 diopters (D), manifest refractive cylinder less than 6.00 D, stable refractive error with less than a 0.50 D change in sphere and cylinder in the previous year, corrected distance visual acuity (CDVA) of 20/20 or better in both eyes, and age of 20 years or older. Exclusion criteria were: severe ocular surface disease, any corneal disease, cataract, glaucoma, macular disease, or previous history of intraocular or corneal surgery. Patients with suspicion of keratoconus on corneal topography were also excluded.