方法：对30例共同性外斜视患者行斜视矫正手术，术中将截除的内直肌用4%甲醛固定后送病理，在显微镜下观察眼外肌的组织结构，并进行HE和Masson染色。

结果：共同性外斜视30例中，内直肌纤维大小不一、形态异常，数量减少，肌肉不同程度的纤维化，经Masson染色后发现，发现斜视较久患者组眼外肌肌纤维含量明显少于发现时间较短患者组(P<0.05)。

结论：斜视的发生与眼外肌的结构异常有关，发现斜视时间较久的共同性外斜视比发现时间较短的共同性外斜视其眼外肌发生明显的纤维化，说明内直肌纤维化可能是外斜视形成的原因之一。随着斜视时间的延长，眼外肌纤维化程度加重。

METHODS: Thirty cases of concomitant exotropia patients were collected to conduct the plastic surgery for strabismus correction. Medial rectus amputated intraoperative were fixed with 4% formaldehyde and then sent to histologic examination. The organizational structure of extraocular muscles was observed, Hematoxylin-eosin(HE)and Masson staining were conducted under microscope.

RESULTS: In the 30 cases, medial rectus muscle fiber presented different sizes, abnormal morphology, number reducing, and the muscle showed varying degrees of fibrosis. After Masson staining, it was found that extraocular muscle fiber content of longer strabismus patients were significantly shorter than that of shorter strabismus patients(P<0.05).

CONCLUSION: The occurrence of concomitant exotropia is related with the abnormal structure of extraocular muscles,with higher extent of fibrosis of extra-ocular muscle in the long period of constant concomitant exotropia than in the late-onset concomitant exotropia. That means the fibrosis of medial rectus probably is the reason of concomitant exotropia. The extent of fiber degeneration change of concomitant exotropia increased with the occurrence of it.