clinical and histopathologic features of consecutive exotropia

purpose: to investigate demographic, clinical and histopathologic features of consecutive exotropia. methods: patients with consecutive exotropia who underwent surgery in farabi hospital between september 2014 and april 2015 were enrolled in this study. after complete ophthalmologic examination and far and near deviation measurement, all patients with negative forced duction test underwent 4-mm medial rectus resection and advancement. intraoperative absence of muscle fiber visualization according to surgeon’s opinion was documented and compared with histopathology results. the histopathologic results were compared between 30 cases of consecutive exotropia and 11 cases who underwent 4-mm resection of the medial rectus muscle with no previous surgery on the medial rectus muscle (controls). a dose-response relationship was calculated for medial rectus resection and advancement in consecutive exotropic patients. results: thirty eyes of 30 patients with consecutive exotropia were evaluated. muscle fibers were not observed intraoperatively in 40% of eyes. no correlation was found between surgical success and the absence of muscle fiber visualization at insertion. dose-response was approximately 4.4 prism diopter per millimeter of resection and advancement of the medial rectus muscle. conclusion: intraoperative absence of muscle fiber visualization was an important cause of consecutive exotropia that could be due to stretched scar and muscle slippage. this could be documented by histopathology using masson trichrome staining. the dose-response relationship calculated in consecutive exotropic patients in the present study can help us better manage these patients. medial rectus underaction may be a risk factor for absence of muscle fiber visualization at insertion. the outcome of surgery can be predicted based on the intraoperative visualization of muscle fiber at insertion.