Medial rectus innervation was always normal, and lateral rectus innervation was always abnormal. Lateral rectus overactivity accompanied deficient adduction. Lateral rectus underactivity accompanied abduction deficiency and was reflected in slowed saccadic abduction movements. Secondary contractures of the medial rectus and lateral rectus were often present. Lateral rectus overactivity with upgaze, downgaze, or both, caused A, V, or X patterns. Retraction on adduction was accompanied by abnormal activity of the superior rectus, inferior rectus, or lateral rectus. Elevation in adduction was usually caused by abnormal superior rectus activity and not abnormal inferior oblique activity. Narrowing of the palpebral fissure only occurred with retraction of the eye. Levator and orbicularis innervations did not change with adduction.
Scott AB, Wong GY. Duane's SyndromeAn Electromyographic Study. Arch Ophthalmol. 1972;87(2):140-147. doi:10.1001/archopht.1972.01000020142005