Clinical and Histopathologic Features of Consecutive Exotropia

Purpose: The purpose of this study is to investigate clinical and histopathologic features of consecutive exotropia. Methods: Thirty patients with consecutive exotropia and negative forced duction testing underwent unilateral medial rectus resection and advancement. Abnormal scleral attachment (appearance of stretched scar or slipped muscle) was documented and compared with histopathology results. The term "stretched scar" is used when tendon-like scar appears between muscle fibers and scleral attachment. The term "slipped muscle" is used when a thin capsule is attached to the sclera and the muscle fibers retracted posteriorly in the capsule. Histopathologic results of resected medial rectus muscles of 11 control patients were compared with cases of consecutive exotropia. Surgical success was defined as <10 PD deviation at both distance and near, 6 months after the surgery. Dose-response and risk factors for abnormal scleral attachment were also evaluated. Results: Forty percent of the cases had abnormal scleral attachment. Nineteen patients (63%) showed successful results. The mean dose-responses were for near 4.7 and for distance 4.2 prism diopters per millimeters of resection plus advancement. Preoperative medial rectus underaction was a risk factor for abnormal scleral attachment. The mean muscle percentage in pathology was 10 +/- 18.7 in patients with abnormal scleral attachment, 28.3 +/- 27.9 in other consecutive exotropia patients, and 26.5 +/- 30.6 in 11 control eyes. Conclusion: This study showed surgical success of 63% with one-muscle surgery in consecutive exotropia. Calculated dose-responses could be helpful in surgical planning. In the cases with preoperative medial rectus underaction, risk of abnormal scleral attachment is increased.