Two different treatments were given to large angle horizontal strabismus (eso and exotropia) adult patients who agree to participate of the study. Inform consents were required for participants. Group 1 (12 patients) received conventional recess-resect surgery plus intraoperative injection of botulinum toxin A (5U). Group 2 (11 patients) received only conventional recess-resect surgery. The patients were randomly located in one of the groups. The angles of horizontal deviation were compared between the groups before and six months after treatment.