Intraindividual optic nerve sheath variation and intracranial pressure changes: a systematic review and meta-analysis

Background and Purpose: To review the existing evidence on multiple timepoint assessments of optic nerve sheath diameter (ONSD) as an indicator of intraindividual variation of intracranial pressure (ICP). Methods: A systematic search identified studies assessing intraindividual variation in ICP through multiple timepoint measurements of ONSD using ultrasonography. Meta-analysis of studies assessing intraindividual correlation coefficients between ONSD and ICP was performed using a random effects model, and we calculated the weighted correlation coefficient for the expected change in ICP associated with variations in ONSD. Results: A total of five studies, comprising 157 patients, were included in the review. ONSD was compared with invasive ICP measurement methods at multiple timepoints. Meta-analysis of intraindividual ONSD–ICP correlation demonstrated a correlation coefficient of 0.62 (CI: 0.50–0.71). Individual linear correlation analyses were performed in two of the studies, yielding correlation coefficients ranging from 0.79 to 1.00; however, widely variable individual slopes were found (1.51–41.43 mm/mmHg). ONSD variations ranged from 0.12 to 3.30 mm per 5 mmHg change in ICP, with a variation of 0.55 mm in adults with hypoxic brain injury and 0.77 mm in children with idiopathic intracranial hypertension. Conclusions: Our findings indicate that ONSD significantly correlates with ICP, and longitudinal intraindividual assessment shows a predominantly linear correlation between both variables. A personalized ONSD–ICP correlation equation may enable accurate ICP prediction, making ONSD a useful tool for follow-up in patients with previous invasive ICP measurements, when adjusted to each patient's characteristics and pathologies.