Esotropia from chronic
sixth nerve palsy or
paresis usually requires surgery.
Chemodenervation of the antagonist medial rectus muscle, while popular for the treatment of acute
sixth nerve palsies and
pareses, has not been used extensively for chronic cases. In this study, 22 patients with
sixth nerve palsies or partially recovered
palsies of greater than 5 months duration were treated with
chemodenervation. The etiologies of the
sixth nerve palsies were
trauma (n = 7),
tumor (n = 4),
infection/
inflammation (n = 3), nerve compression from
aneurysm or increased intracranial pressure (n = 4), congenital (n = 1),
ischemia (n = 2), and idiopathic (n = 1). The mean preinjection deviation was 41 prism diopters. A total of 38
injections were administered (mean, 1.7 per patient). Each patient received an injection of 2.5 to 7.5 units (mean, 4.1) of
botulinum neurotoxin A to the ipsilateral medial rectus muscle. Treatment success was assessed 6 months after the last injection. A course of
chemodenervation significantly improved the alignment of 9 of the 22 patients (41%). The mean postinjection deviation was 8 delta. Seven patients (32%) had single binocular vision in primary position restored. These patients had a mean horizontal
binocular field of 70 degrees (range, 40 degrees to 100 degrees). Thirteen patients (59%) had only modest improvement and required surgery. The data suggest that injection of
botulinum neurotoxin A is a useful treatment for some patients with chronic sixth nerve weakness. A course of
chemodenervation therapy compares less favorably with transposition surgery with concomitant
neurotoxin injection for the treatment of these difficult problems.