To report a case of iatrogenic exotropia caused by accidental excision of medial rectus muscle during functional endoscopic sinus surgery (FESS), which was successfully corrected by sequential surgical intervention (superior and inferior rectus muscle transposition followed by lateral rectus muscle recession).

Forty one year old male patient visited our clinic with large exotropia of the right eye developed after functional endoscopic sinus surgery (FESS) which was performed one year ago. At the initial visit in our clinic, there was a large exotropia (95 PD) of the right eye and transection of the medial rectus muscle was observed at the orbital MRI. In order to correct this large iatrogenic exotropia, sequential surgery was planned. Initially, full-tendon transposition of the right superior and inferior rectus muscle was performed which reduced the deviation to 35 PD. Six weeks after the initial surgery, 7 mm right lateral rectus muscle recession was additionally performed, which resulted in exotropia of 10 PD. Diplopia was also improved and the patient was esthetically satisfied with the result.

Even in a case of iatrogenic exotropia following one year after an accidental excision of medial rectus muscle during intranasal sinus surgery, sequential surgery such as transposition of superior and inferior rectus muscle followed by lateral rectus muscle recession can result in satisfying cosmetic and functional improvement.