Impact of gaze deviation on the optic nerve sheath diameter metric: A prospective interventional study

Giada Cucciolini; Gaia Mignani; Giulio Costanzo; Francesco De Masi; Francesco Forfori; Francesco Corradi

doi:10.5826/tuj.2026.18767

Impact of gaze deviation on the optic nerve sheath diameter metric: A prospective interventional study

Authors

Giada Cucciolini University of Pisa
Gaia Mignani Department of Clinical and Experimental Medicine, Neurology Unit, University of Pisa, Pisa, Italy https://orcid.org/0009-0005-2098-3467
Giulio Costanzo Department of Surgical, Medical, Molecular Pathology and Critical Care Medicine, University of Pisa, Via Savi 10, 56126, Pisa, Italy
Francesco De Masi Departmental Structure of Neuroanesthesia and Intensive Care, Via Paradisa 2, 56124, Pisa, Italy https://orcid.org/0009-0000-6034-6044
Francesco Forfori Department of Surgical, Medical, Molecular Pathology and Critical Care Medicine, University of Pisa, Via Savi 10, 56126, Pisa, Italy https://orcid.org/0000-0001-8201-8076
Francesco Corradi University of Pisa, ATS Liguria-ASL5 Spezzino, Ospedale Civile Sant'Andrea, La Spezia https://orcid.org/0000-0002-5588-2608

Keywords:

ONSD, Point of Care Ultrasound, Neurocritical care, Ocular ultrasonography, ONSD squeeze, 30-degree test, gaze

Abstract

Background: Optic nerve sheath diameter (ONSD) is a widely used non-invasive surrogate marker of intracranial pressure. Current recommendations state that measurements should be obtained with a neutral gaze. However, the effect of gaze deviation on ONSD has never been investigated. We aimed to evaluate the reliability of ONSD in case of gaze deviation and quantify the associated measurement error. A secondary aim was to assess whether bed inclination has a significant effect on ONSD values.

Methods: We conducted a prospective interventional study on 44 healthy volunteers during routine ocular ultrasound training. ONSD was measured bilaterally along the horizontal and vertical axes at 45° head-of-bed elevation in neutral and deviated gaze. After repositioning the bed to 0° and a 2-minute stabilization period, horizontal measurements were repeated. Measurements were performed according to current consensus recommendations and ALARA principles. Nonparametric analyses were used to analyse the results.

Results: Gaze deviation significantly reduced ONSD values across all axes and both eyes, with a consistent median difference of 0.8–1.0 mm (all p < 0.001) and large effect sizes. In contrast, no significant differences were observed between measurements obtained at 45° and 0° (p > 0.5).

Conclusions: Gaze deviation induces a predictable “stretching” effect on the optic nerve sheath, resulting in clinically relevant ONSD reduction. If confirmed in neurocritical populations, this systematic difference may allow estimation of neutral-gaze ONSD in non compliant patients and could form the basis for a dynamic test that estimates optic nerve sheath compliance.

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