Consecutive strabismus after infantile nystagmus syndrome surgery and potential risk factors

Purpose The aim of this study is to evaluate the incidence of consecutive strabismus after infantile nystagmus surgery and its potential risk factors. Methods A retrospective study including 89 patients was conducted. Patients presented infantile nystagmus (idiopathic or ocular disease-associated nystagmus) without previous or coincidental strabismus. Sex, age at surgery, amblyopia, botulinum toxin (BT) injection before surgery, spherical equivalent, anisometropia, surgery procedure (Anderson's or retroequatorial recessions of four horizontal recti), and follow-up were analyzed. Kaplan-Meier and univariate Cox regression were performed. Results The median age at surgery was 5 years. The median follow-up was 36 months. The incidence of consecutive strabismus was 11.2%. There were eight patients with exotropia and two patients with esotropia. Consecutive strabismus was associated with severe bilateral amblyopia (p = 0.036), previous treatment with BT injection (p = 0.025), and large recessions of the four horizontal muscles (p = 0.001). The hazard ratio for patients with severe bilateral amblyopia was 5.4 (95% CI 1.1-25.8), and for patients previously treated with BT was 6.1 (1.3-29.3). The survival rate was 95.4% at 6 months and 88.5% at 3 years. Conclusion Severe bilateral amblyopia, previous BT treatment, and type of surgery seem to be associated with consecutive strabismus after infantile nystagmus surgery. Most cases appear within the first months after surgery.