Increased restriction from an accessory lateral rectus in exotropic Duane syndrome.

Supernumerary extraocular muscles can cause restrictive strabismus, unusual ocular movements, and a persistent positive forced duction test. Even among patients with clinically typical strabismus, intraoperative testing and surgical exploration may reveal the presence of supernumerary extraocular muscles. We report the case of a patient with exotropic Duane syndrome found intraoperatively to have an accessory lateral rectus muscle, with histopathologically confirmed striated fibers.