Described herein are the cases of 2 patients who underwent bilateral femtosecond-assisted laser in situ keratomileusis (FS LASIK) surgery and subsequently developed unilateral postLASIK ectasia. The fellow eye of both patients was topographically normal, their visual acuity was 20/20, and the patients had no visual symptoms. However, a biomechanical assessment using the Corvis ST tonometer (Oculus Optikgerate GmbH; Wetzlar, Germany) revealed remarkable weakness not only in the ectatic eyes, but also in the fellow eye. Arrangements were made to perform corneal crosslinking for the eyes with manifest ectasia and close follow-up of the fellow eyes.