ABSTRACT
Objective. To analyse the factors influencing the favourable outcome of botulinum toxin treatment of exotropia. Methods. Nineteen exotropic patients aged between 13–274 months were treated with simultaneous bilateral injections of 20 U of botulinum A toxin (Dysport, Ipsen Ltd, Maidenhaed, England). 12 patients underwent 1 bilateral injection and 7 underwent multiple bilateral injections injected under electromyographic monitoring with audible and visible trace. Patients were followed up for 24 to 60 months after the last injection. The following parameters were analysed: aetiology of exotropia (primary or consecutive), size of exotropia, convergence weakness, potential binocular vision, age of first injection, transient overcorrection (eso shift). Results. The results of our study are summarized in Table 1. Motor success was obtained in 12 (67%) and 13 (72%) patients for distance and near vision respectively (Table 2). Convergence weakness. We have compared a basic exotropia group with a convergence weakness group. In the basic exotropia group mean preinjection deviation decreased of 21 and 16 Prismatic Diopters to 6 and 4 PD for distance and near deviation respectively with a percentage of correction of 69 % both for distance and near vision. In the convergence weakness group deviation decreased of 17 and 21 PD to 11 and 12 PD for distance and near vision respectively with a percentage of correction of 43% (Table 3). Potential binocular vision. The mean percentage of correction was 48% and 51% for distance and near vision respectively for patients without preoperative binocular vision. For patients who had preoperative binocular vision the mean percentage correction was 64% and 52% for distance and near vision respectively. Transient overcorrection (eso shift). The mean percentage of correction was 75% and 68% for distance and near respectively for patients with transient overcorrection (Table 4), increasing to 86% and 76% for basic exotropia group. The mean percentage of correction was 58% and 56% for convergence weakness group. Conclusion. Our preliminary results suggest that convergence weakness, transient post injection overcorrection (eso shift) and preoperative fusion are useful predictors of the favourable outcome of botulinum toxin treatment of exotropia.
