Correlation between Optic Nerve Sheath Diameter Measured by POCUS and Neurological Deficit in Physical Examination in Adult Patients with Suspected Ischemic Stroke Evaluated in Emergency Departments

Background: Rapid and accurate lateralization of neurological deficits is critical in the acute management of stroke and other neuro-emergencies. Optic nerve sheath diameter (ONSD), assessed by ultrasound, is a non-invasive marker of intracranial pressure. However, its role in detecting hemispheric asymmetry and predicting the side of neurological focalization remains poorly defined. Methods: We conducted a prospective observational study including 19 adult patients presenting with acute neurological deficits to the emergency department of Clínica México. Bilateral ONSD was measured using ocular ultrasound, and asymmetry was calculated as Δ ONSD = right ？ left. The primary outcome was the correlation between Δ ONSD and the side of neurological focalization on physical examination. Secondary outcomes included associations with stroke severity (NIHSS), neurological improvement, and diagnostic accuracy. Data were analyzed with Wizard Pro software. This protocol was registered at ClinicalTrials.gov (NCT06492681). Results: The mean age of patients was 68.4 ± 11.1 years, with 57.9% males. The main comorbidities were hypertension (73.7%), diabetes (36.8%), and previous stroke (36.8%). A significant correlation was found between Δ ONSD and the side of focalization (p < 0.01). Patients with left-sided deficits had positive Δ values, while those with right-sided deficits had negative values. ROC analysis demonstrated an AUC of 0.91, with an optimal cutoff of Δ ≈ +1.0 mm, yielding sensitivity 85.7% and specificity 90%. No significant association was observed between Δ ONSD and NIHSS score (p = 0.48) or short-term neurological improvement (p = 0.76). Conclusions: ONSD asymmetry measured by ultrasound was strongly associated with the side of neurological focalization in patients with acute stroke symptoms. This bedside, non-invasive tool may provide rapid lateralization when advanced imaging is unavailable or delayed. Larger multicenter studies are needed to validate these preliminary findings and to explore integration of ONSD asymmetry into multimodal stroke triage protocols.