Persisting hypotropias following protective ptosis induced by botulinum neurotoxin

Botulinum toxin A induced ptosis (BTXAP) has become an established method for producing a temporary ptosis for corneal protection. Adams et al1 reported from an initial series of 15 patients and observed that the ptosis lasted for a mean period of 2.5 weeks and that full recovery was achieved after a mean of 8.1 weeks. They noted that in 80% of cases there was a temporary superior rectus weakness which lasted for a mean of 6 weeks. We present three cases in which the superior rectus weakness was permanent and required corrective strabismus surgery. We believe that these are the first cases reported. We propose two possible mechanisms which may be acting together: firstly that a prolonged period of occlusion may have led to a breakdown of fusion, and secondly that following botulinum toxin induced superior rectus weakness there was contracture of the ipsilateral antagonist muscle further disrupting fusional mechanisms.