Background: Ocular point-of-care ultrasound (POCUS) may be a clinically useful method to evaluate shunt dysfunction for children with hydrocephalus in the emergency department (ED). We assessed whether a change in optic nerve sheath diameter (ONSD) from prior asymptomatic baseline is associated with shunt failure. Methods: This prospective single center cohort study included asymptomatic shunted children (age 0-18 years). Baseline ocular POCUS was performed in the outpatient neurosurgery clinic; a second POCUS was performed if the patient subsequently presented to the ED with symptoms of shunt failure. Shunt failure was defined by intraoperative confirmation of inadequate CSF flow through the shunt within 96 hours from ED presentation. Results: The primary outcome of intra-operatively confirmed shunt failure occurred in 14/76 (18%) ED patient presentations. ΔONSD in patients with and without shunt failure was 0.89mm and 0.16mm respectively; the mean difference was 0.73mm (95%CI: 0.34-1.12), p=0.0012. The area under the receiver operating characteristic curve was 0.86, with an optimal cutoff of ≥+0.4mm, corresponding to sensitivity of 0.93, specificity of 0.73, PPV of 0.43, NPV of 0.98. Conclusions: ΔONSD was strongly associated with shunt failure. We found ΔONSD of <+0.4 in symptomatic children with CSF shunts may identify a population that had low likelihood of true shunt failure.