Synoptometer analysis of vertical shoot in Duane's retraction syndrome

Vertical deviation of the affected eye caused by horizontal change of gaze was measured with a synoptometer in 5 cases of Duane's retraction syndrome type III. Step-by-step measurement clearly showed two types of incomitance patterns, i.e. upshoot and up- and downshoot in adduction. The former suggests a paradoxical synergistic innervation between the medial rectus and superior rectus muscles, and the latter suggests an abnormal vertical movement of the lateral rectus muscle over the globe on elevation or depression of the eye. Recession of the lateral rectus muscle, however, reduced the vertical deviation regardless of the incomitance pattern.