Optic nerve sheath diameters in healthy adults measured by computer tomography

Abstract

Aim: To measure optic nerve sheath diameters (ONSD) in different locations by computer tomography (CT) and to recommend the best location for cases when ONSD is used for intracranial pressure monitoring.

Methods: In a prospective cohort study, CT data of 300 healthy adults were analyzed (600 eyes). In all cases, the CT investigation was performed at the Emergency Department because of the various conditions that proved not to be connected with ophthalmological or neurological pathology. The ONSD were measured at 3 mm and 8 mm distance from the globe, and 3 mm from the anterior opening of the optic canal. The correlation analysis was performed with gender, age, and ethnic background.

Results: The right/left ONSD are 4.94±1.51/5.17±1.34 mm at 3 mm, 4.35±0.76/4.45±0.62 mm at 8 mm from the globe, and 3.55±0.82/3.65±0.7 mm at 3 mm from the optic canal. No significant differences correlated with gender of the patients, their age, and ethnic background were found.

Conclusion: In healthy persons, the ONSD varies from 5.17±1.34 mm to 3.55±0.82 mm in different locations within the intraorbital space. The most stable results with lesser standard deviation can be obtained if it is measured 8-10 mm from the globe.

Keywords: computer tomography; intracranial pressure; optic nerve sheath.

Figure 1. Optic nerve sheath diameters as measured by CT in transverse projection

ONSD in various locations is indicated in mm (4.3 mm: ONSD at the middle third of the orbital path of the optic nerve; 6.2 mm: ONSD 3 mm behind the globe). At this picture, the left ONSD was measured precisely (6.2 mm), and the 4.3 mm represents preliminary detection of the right optic nerve sheath that was measured precisely at the following CT scan slices.

Figure 2. The measurement of the ONSD at its distal location, 3 mm behind the globe.