Saccadic eye movements and force development in Duane's retraction syndrome

Abstract

In nine patients with Duane's retraction syndrome (DRS), eight unilateral and one bilateral, horizontal and vertical saccadic movements of each eye were recorded using electro-oculography (EOG) during monocularly elicited saccades with the affected or the non-affected eye fixating. Corresponding force development of the affected eye in the horizontal and vertical directions was measured by means of a contact lens/strain gauge technique. Different types of abnormal saccadic movements for each eye were observed, including hypermetric multiple-step saccades, glissadic saccades, hypometric restrictive saccades, etc. Reduced saccadic peak velocity was found in the affected eye, and prolonged saccadic duration and reduced saccadic mean velocity in the non-affected eye, indicating abnormal saccadic control in both eyes. Decrease of horizontal force production of adduction and abduction in the abduction field of gaze was found in the affected eye, but normal peak force of adduction in the adduction field of gaze was preserved. Vertical saccadic movements were normal in velocity, and no significant changes in dynamic parameters of vertical force production were found. Significant concurrent horizontal force productions were seen during vertical movements. Abnormalities of saccadic movements and tension development of the affected eye are most likely due to co-contraction of the medial and lateral recti. However, horizontal force development during vertical movements may indicate the existence of mechanical or innerva-tional interaction between vertically and horizontally acting muscles.