This study is a single-center, prospective, randomized, controlled trial. To investigate whether preoperative using of eye patches will decrease emergence agitation or not, and to provide a better method of decreasing emergence agitation to pediatric ophthalmic anesthesiologists. The investigators will recruit 180 children undergoing elective cataract surgery, divided into 2 groups by random method. experimental group will cover the effected eye for 3 hours before the operation, while the control group will not. Then the investigators will observe and mesure the incidence of emergence aditation in each group, to assess whether preoperative patch shading can reduce the incidence of postoperative agitation.