Vertical rectus muscle transposition and botulinum toxin for complete sixth nerve palsy

Effective surgical treatment of complete unrecovered sixth nerve palsy must include the transfer of abducting power to the temporal aspect of the globe with release of medial rectus contracture nasally. We describe our experience in the treatment of five such patients who underwent full vertical rectus transposition combined with botulinum toxin chemodenervation of the ipsilateral medial rectus muscle.

The five patients all had primarily unilateral complete unrecovered sixth nerve palsy. They all underwent a complete preoperative and postoperative eye examination and an orthoptic assessment. Excursion into abduction was graded from -8 (globe immobilized in extreme adduction) to -4 (abduction as far as primary position) to 0 (full abduction). Abduction saccades and a forced muscle generation test confirmed the presence of complete unrecovered sixth nerve palsy, and forced duction testing measured the degree of medial rectus contracture. All patients received ipsilateral medial rectus injection of botulinum toxin in the preoperative (8 to 2 months before surgery) and perioperative periods, and underwent complete superior rectus-inferior rectus transposition temporally.

The average length of follow-up was 21 (range 6 to 48) months. The average preoperative distance alignment was 52 (range 25 to 80) prism dioptres (PD). Vertical rectus transposition combined with botulinum toxin injection resulted in an average distance alignment change of 66 PD (range 50 PD to 82 PD) of exoshift. The average final deviation was 1 PD of esotropia (range 4 PD of esotropia to 6 PD of exotropia). Average abduction improved from -6 (range -3 to -8) preoperatively to -1.7 (range -1 to -2) postoperatively. Saccades averaged -4 preoperatively and improved to -2 postoperatively. Normal vertical eye movements were preserved in all patients. A total field of single binocular vision was created in all patients, which averaged 55 degrees (range 30 degrees to 75 degrees) in the horizontal meridian. The field of single binocular vision from primary position into abduction averaged 23 degrees (range 18 degrees to 28 degrees).

Temporal transposition of the vertical rectus muscles combined with perioperative botulinum toxin injection of the ipsilateral medial rectus muscle is a reliable and effective way of restoring functional binocular vision in patients with complete unrecovered sixth nerve palsy.