Relative risk and onset of strabismus in children with Chiari malformation.

PURPOSE: To determine relative risk, onset, and types of strabismus in patients with Chiari malformation. METHODS: In this retrospective cohort study of children (<18 years of age) seen at a pediatric ophthalmology practice over 15 years, we identified patients diagnosed with Chiari malformation on brain imaging. Strabismus diagnoses were first determined with diagnostic codes and confirmed via chart review in patients with Chiari. Risk factors for strabismus, including Chiari type, Chiari-related symptoms, hydrocephalus, neurosurgery, and other structural brain abnormalities were evaluated using multivariable analysis. Primary outcome was relative risk of strabismus compared between children with and without Chiari seen at the same clinic. Cumulative probability of strabismus by age was evaluated with Kaplan-Meier analysis. Secondary outcomes were risk factors, onset, and types of strabismus in children with Chiari. RESULTS: Of 149,141 children studied, 591 had Chiari malformation (286 type I, 302 type II, 3 type III). Risk of strabismus was higher among children with Chiari (226/591 [38%]) versus without (27,297/148,550 [18%]) (relative risk = 2.1; 95% CI, 1.9-2.3; P < 0.001). Significant risk factors were hydrocephalus (OR = 2.9; 95% CI, 1.8-4.9) and structural brain abnormality (OR = 2.3; 95% CI, 1.5-3.6). Cumulative prevalence of strabismus at ages 1, 5, 10, 15 years were 5%, 17%, 27%, 36% for Chiari type I; 10%, 36%, 45%, 55% for Chiari type II/III; respectively. Most common strabismus types were exotropia, accommodative esotropia, and nonaccommodative esotropia; clinicians attributed only 8% of strabismus directly to Chiari, usually along with concurrent cranial nerve palsy. CONCLUSIONS: Children with Chiari malformation have increased risk of strabismus compared to those without, even after controlling for referral bias among children in a pediatric ophthalmology clinic. Early ophthalmology referral is recommended.