Minimal invasive vertical muscle transposition for the treatment of large angle exotropia due to congenital medial rectus hypoplasia

Purpose: Strabismus related to congenital abnormalities of extraocular muscles(EOM) is rare. Different forms of aberrations of the EOMs have been reported, ranging from aplasia, hypoplasia as well as supernumerary band. There are a few reports of isolated anomalies of the medial rectus muscle. In this study, we report a case of hypoplastic medial rectus in an adult with favorable surgical outcome. Methods: A 43‑year‑old man presented with large‑angle right exotropia noted since childhood and a significantleft face turn. He had an absence of right eye adduction (−6 on a scale of 0 to -8) while other ductions were present. The patient was otherwise healthy with no history of systemic disease. An interesting finding was increased palpebral fissure height resembling proptosis in the right eye. In the preoperative CT scan, all EOMs seemed normal. He underwent surgery in the right eye. Forced duction test did not reveal tightness of lateral rectus muscle. First, the lateral rectus muscle was recessed largely. Exploration revealed of a translucent band without muscles fibers in the site of medial rectus. With the new technique of transposition myopexy, the vertical muscles were secured to the sclera 8 mm posterior to the medial rectus site without splitting or tenotomy of the muscles. Results: Good correction of the exotropia was obtained in the primary position. The adduction was improved from -6 to -4. The palpebral fissure height asymmetry was corrected as well. Conclusion: Imaging is useful in identifying these unusual anomalies but may be a discrepancy between the preoperative imaging and the intraoperative findings as we showed here. Furthermore, with minimal invasive method originally described by Nishida, by changing the vector of vertical rectus muscles without splitting or tenotomy in cases of complete duction limitation, a large angle deviation can be corrected. Also, the risk of anterior segment ischemia is minimal.