DISSOCIATED EFFECTS OF BOTULINUM TOXIN CHEMODENERVATION ON OCULAR DEVIATION AND SACCADE DYNAMICS IN CHRONIC LATERAL RECTUS PALSY

Aim-Changes in saccade velocity/amplitude characteristics (main sequen ce) and attenuation of distance esotropia in response to botulinum tox in (BTX-A) chemodenervation of the antagonist medial rectus were studi ed in a group of nine patients with chronic lateral rectus palsy. Meth ods-Serial measurements of ocular deviation and infrared oculograms of saccadic eye movements Ito targets at 5 degrees-20 degrees of lateral gaze were made before injection and at 2, 4, 8, 16, and 20 weeks afte r injection. Results-At 2 weeks after injection, the ocular deviation changed by at mean of 34.5 prism dioptres and the 5 degrees and 10 deg rees adduction saccades were significantly slowed (p<0.02 Wilcoxon sig ned rank test). By the second examination, however, the adducting sacc ade peak velocity had returned to normal while the mean ocular deviati on remained significantly changed (p=0.01 Wilcoxon matched pairs). By 20 weeks the mean ocular deviation was not significantly different fro m that before injection (p=0.14 matched pairs). Conclusions-The ocular realignment caused by BTX-A may persist after saccadic function has b een restored. This may be because toxin may have a more profound and l ong lasting effect on the orbital singly innervated fibres which are a ctive tonically at rest to hold gaze whereas there is relative sparing of the additional motor units recruited during fast eye movements.