To investigate clinical and histopathologic features of consecutive exotropia.

Thirty patients with consecutive exotropia and negative forced duction testing underwentunilateral medial rectus resection and advancement. Abnormal scleral attachment (appearance of stretched scar or slipped muscle) was documented and compared with histopathology results. Histopathologic results of resected medial rectus muscles of 11 control patients were compared with cases of consecutive exotropia. Success rate, dose-response, and risk factors for abnormal scleral attachment were evaluated.

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 forabnormal scleral attachment.The mean muscle percentage in pathology was 10±18.7 in patients withabnormal scleral attachment, 28.3±27.9 in other consecutive exotropiapatients, and 26.5±30.6 in 11 control eyes.To predictabnormal scleral attachment, best cut-off for muscle percentage in pathology was 18% and for scar percentage was 72.5%.

With surgical success of 63% and one-muscle surgery, we can suggest this 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 increased. The cut-off points for muscle and scar percentages can help pathologic diagnosis ofabnormal scleral attachment.