Accessory lateral rectus muscle in a patient with congenital third-nerve palsy

PURPOSE: To report a case of accessory lateral rectus muscle in a patient with congenital third-nerve palsy. DESIGN: Observational case report. METHODS: An 18-year-old boy with left exodeviation, ptosis, pupil dilation, and limited adduction, supraduction, and infraduction of his left eye. Left lateral rectus muscle recession and medial rectus muscle resection were done. An orbital computed tomographic (CT) scan was obtained. RESULT: Intraoperatively, an accessory muscle was found under the lateral rectus muscle. Postoperatively, the orbital CT scan showed accessory lateral rectus muscle located in the medial side of the lateral rectus muscle. CONCLUSION: Accessory lateral rectus muscle was demonstrated in a patient with congenital third-nerve palsy using lateral rectus muscle surgery and an orbital CT scan.