Abnormal medial rectus insertion presenting exotropia: a case report and review of the literature

Dear Editor, I am Dr. Heeyoung Choi, from the Department of Ophthalmology of Pusan National University Hospital, Busan, Korea. I write to present a case report of abnormal medial rectus insertion presenting exotropia. Isolated anatomical abnormalities of the extraocular muscles without craniofacial syndromes or other systemic anomalies are not common. In most of the cases, strabismus is usually combined with incomitance and abnormal ocular movement. There are a few reports of isolated anomalies of the medial rectus muscle . We report a case that an exotropic patient with abnormal insertion of the medial rectus muscle who achieved successful surgical outcome. A 16-year-old boy was referred to our clinic because of exotropia. He first noticed his eyes exodeviated when he was 7 years old. He denied any treatment, both non-surgical and surgical. His best corrected visual acuity was 20/40 in the right eye and 20/20 in the left eye. Refractive error was +0.5 diopters in the right eye and -1.0 diopters in the left eye. He had constant exotropia of 40 prism diopters upon distance and near fixation testing by prism and alternative cover test. He had poor stereoacuity (200 seconds of arc) which was evaluated by the titmus test. His near point of convergence was 30 cm. Duction and version was within normal range. He did not have any systemic disease or previous history of ophthalmic surgery. We planned to perform right lateral rectus recession combined with right medial rectus resection. There were no abnormal findings in intraoperative forced duction test. After performing 7.5 mm of recession of the right lateral rectus muscle, which was normally inserted, we noticed that the right medial rectus was attached to the sclera 12 mm from the limbus. The muscle itself looked healthy and of a normal size. The left medial rectus muscle was also attached 12 mm away from the limbus (Figure 1). This finding required a modification of the planned surgical procedure. Instead of resection, we decided to perform advancement of the medial rectus by 5 mm. Limitation of ocular movement or symptomatic diplopia was not occurred after surgery. One year after surgery, the patient maintained orthotropia (Figure 2). There are only a few reports about anomalies of the medial rectus muscle, presenting comitant strabismus . Choi [2]