Botulinum toxin injection for postoperative diplopia testing in adult strabismus

PURPOSE To investigate the use of botulinum toxin type A in identifying adult patients with constant strabismus who are at high risk of developing intractable diplopia after surgery. METHODS A retrospective review of adult patients with constant horizontal strabismus who had botulinum toxin injection to evaluate their risk of postoperative diplopia. These patients reported diplopia when prisms were used to neutralize the deviation. RESULTS One hundred ninety-five adults were studied; their mean age was 40.3 +/- 14 years (range, 16 to 73 years). One hundred thirty-three (68%) had botulinum. toxin injected into a lateral rectus muscle; 62 (32%) had injections in a medial rectus muscle. Only 14 (7%) developed diplopia; 9 (4.6%) of these had troublesome diplopia but 5 (2.6%) could cope with the double vision and elected to have surgery. Surgical correction was recommended to the remaining 181 (93%) who did not experience diplopia. Complications of botulinum toxin injection were ptosis (10 patients, 5.1%) and superior oblique muscle weakness (3 patients, 1.5%). Twenty-six patients (13.3%) had a poor response to the first injection and required a second injection with a double dose. Surgery did not result in intractable diplopia after 6 weeks in any patient with a negative botulinum toxin diplopia test. CONCLUSIONS Botulinum toxin is a useful diagnostic tool for identifying patients with a low risk or no risk of postoperative diplopia despite a positive prism diplopia test.