Objective To explore the effects of different lengths of time for visual preconditioning (application of an eyepatch over the eye to be operated the day before surgery) on emergence delirium after ophthalmic surgery under general anesthesia in preschool-aged children. Methods A prospective study was conducted.Preschool-aged children undergoing elective ophthalmic surgery with general anesthesia were recruited.Children in one unit received visual preconditioning after video education, while their counterparts in the other unit only watched video for health education (control group).The Modified Yale Preoperative Anxiety Scale, Nursing Delirium Screening Scale, Wong-Baker Faces Pain Rating Scale and Postoperative Nursing Difficulty Score were utilized to measure the effects. Results Totally, 189 children completed visual preconditioning for 30-89 min, 133 for 90-179 min, and 72 for ≥180 min.Compared with the control group (n=146), the visual preconditioning groups had significantly lower incidence of emergence delirium, and also lower scores of m-YPAS, NU-DESC and nursing difficulty (P＜0.01 for all).There were no significant diffe-rences among the visual preconditioning groups (P＞0.05,P＞0.0083). Conclusion Prophylactic eyepatch treatment can reduce emergence delirium in preschool children undergoing general anesthesia for ophthalmic surgery.Visual preconditioning for 30-179 min is as effective as ≥180 min.