The role of botulinum toxin in third nerve palsy

Isolated third nerve paresis is a rare diagnosis among patients presenting to the Botulinum Toxin Clinic at Moorfields Eye Hospital. Ten patients with this diagnosis are reviewed in this study. Head trauma is a common cause of third nerve palsy and is often severe enough to cause damage to fusion potential. If fusion is present and there is adequate adduction of the divergent eye, then botulinum toxin injection of the lateral rectus may induce long-term control of the ocular deviation. Three of the four patients who experienced long-term control of their ocular deviation following toxin injection shared these features. Toxin injected into the lateral rectus did not, however, reliably assess medial rectus function and therefore predict the outcome of horizontal squint surgery. Reasons for this are discussed.