Optic nerve sheath diameter asymmetry in healthy subjects and patients with intracranial hypertension

Background: Ultrasonography of the optic nerve sheath diameter (ONSD) is used for the non-invasive assessment of increased intracranial pressure (ICP). ONSD values are usually obtained by averaging the measurements of the two eyes, but asymmetric ONSD dilation is possible, leading to potentially inaccurate ICP estimation when using binocular averaging. In addition, few data are available about the asymmetry of the ONSD and the use of the maximum ONSD value between eyes for raised ICP detection. The aim of the study was to evaluate the interocular ONSD asymmetry in healthy subjects and patients with intracranial hypertension (IH) by ultrasonography and to investigate whether the maximum ONSD could be as useful as the binocular assessment. Methods: Forty healthy subjects and 40 patients with IH (20 with idiopathic intracranial hypertension and 20 with intracerebral hemorrhage) who underwent transorbital sonography were retrospectively enrolled. The prevalence and degree of ONSD asymmetry were compared among groups; ONSD median binocular and maximum values were compared. Results: Forty-two out of 80 subjects (52.5%) showed significant ONSD asymmetry, without significant differences in prevalence among groups (p = 0.28). The median asymmetry was higher in patients than in healthy subjects (0.45 mm vs 0.23 mm; p = 0.007), without significant differences between the two pathologies (p = 0.58). Both binocular and maximum ONSD measurements were significantly higher in patients with IH than in controls (p < 0.001). Conclusions: Interocular ONSD asymmetry occurs both in healthy subjects and, more consistently, in patients with IH. Both binocular and maximum ONSD may be useful markers for increased ICP detection.