Optic Nerve Sheath Diameter: Correlation With Intra-Ventricular Intracranial Measurements in Predicting Dysfunctional Intracranial Compliance

Background Ultrasonographic (USG) measurement of optic nerve sheath diameter (ONSD) has been proposed as a non-invasive, bedside method to detect raised intracranial pressure (ICP) in various clinical settings. We aimed to correlate the ONSD obtained from ultrasonography with the gold standard, intraventricular ICP, and to find out the cut-off point which predicts ICP accurately at different levels. Methodology A prospective double-blind study was carried out by performing ocular ultrasounds in 30 adult patients with features of intracranial hypertension. The ONSD was measured by USG intraoperatively along with direct intraventricular pressure measurement. The ONSD was compared with the intraventricular ICP and correlations were derived. The optimum cut-off of ONSD to predict ICP > 20 mm Hg, 25 mm Hg, 30 mm Hg, and 35 mm Hg was sought. Results There was a significant correlation of ONSD with ICP (r = 0.532, p = 0.002). An ONSD threshold of 5.5 mm predicted ICP > 20 mm Hg with high sensitivity (100%) and specificity (75%) (area under receiver operating characteristic [ROC] curve = 0.904, p=0.01). The optimum ONSD cut-off predicting ICP at values of 25 mm Hg, 30 mm Hg, and 35 mm Hg was 6.3 mm, 6.5 mm, and 6.7 mm, respectively. Conclusion Our study confirms the utility of optic nerve ultrasound in the diagnostic evaluation of patients with known or suspected intracranial hypertension. We recommend an ONSD cut-off of 5.5 mm for predicting ICP > 20 mm Hg.