A magnetic resonance imaging study of the upshoot-downshoot phenomenon of Duane's retraction syndrome.

Abstract

Patients with Duane's retraction syndrome may have an associated upshoot or downshoot of the involved eye in adduction. This vertical movement has been attributed to the lateral rectus muscle slipping over or under the globe and acting as an elevator or depressor, respectively ("bridle-effect"). We used magnetic resonance imaging to investigate this phenomenon in two patients, one with an overshoot and the other with an undershoot. Minimal vertical displacement of the lateral rectus muscle in relation to the orbit was noted both on upshoot and downshoot. The bridle-effect theory must be modified to account for this finding.