Botulinum toxin injection in the management of lateral rectus paresis.

Seventeen patients with lateral rectus paresis (3 bilateral) were treated by injection of botulinum toxin to the antagonist medial rectus to eliminate its unopposed action or to eliminate its contracture. This allowed maintenance of single binocular vision in most patients while waiting for the palsy to heal, especially important in two children. It allowed avoidance of surgery in some cases, and a reduction or elimination of medial rectus surgery when later intervention was needed for persistent paralysis. The release of medial rectus shortening and stiffness (contracture) after just a few days of denervation was unexpected. This implies an internal muscular mechanism of contracture, perhaps sarcomere overlap, different from the fibrotic changes found in muscles after inflammation or trauma. These results also provide a rationale for experimental denervation treatment of contracture in limb muscle disorders.