OBJECTIVE To analyze the relationship between changes in the intraocular pressure (IOP) and dislocation angle in highly myopic strabismus patients who had undergone muscle union surgery. METHODS Medical data were examined of eight eyes of seven consecutive patients with highly myopic strabismus, who had some limitation in abduction, received muscle union surgery and undergone pre- and postoperative IOP evaluation with a noncontact tonometer, and were retrospectively reviewed. In addition, 15 eyes of 15 patients with comitant horizontal strabismus who underwent unilateral recess-resect procedure as well as pre- and postoperative IOP evaluation were also included. The correlation between IOP changes after strabismus surgery and the dislocation angle of the globe was analyzed. RESULTS The IOP was significantly reduced in the highly myopic strabismus group (-5.6 mmHg) but not in the fellow eye or in comitant horizontal strabismus patients. The decrease in IOP after surgery was significantly correlated with the preoperative dislocation angle of the globe (r = -0.725, p = 0.042). CONCLUSIONS IOP is often higher in highly myopic strabismus patients than perceived, and it may indicate abnormal anatomy of the orbit rather than glaucoma. In that case, muscle union surgery can improve eye position and normalizes the IOP.