Sonographic Assessment of Optic Nerve Sheath Diameter for Increased Intracranial Pressure 
Surafel Dubale, Yohannes Seife, Robel Beyene  
 
OPEN MANUAL OF SURGERY IN RESOURCE-LIMITED SETTINGS 
www.vumc.org/global-surgical-atlas 
This work is licensed under a Creative Commons Attribution-Share Alike 3.0 Unported License  
 
Introduction:  
Optic nerve sheath diameter measurement is 
a non-invasive, time saving, and efficient way of 
assessing raised intracranial pressure in a patient 
with altered consciousness of unknown etiology. 
The optic nerve sheath demonstrates changes in 
diameter with intracranial pressure changes, as there 
is a layer of subarachnoid space between the nerve 
and its sheath, which expands due to raised 
intracranial pressure. These changes are appreciated 
more along the anterior aspect of the nerve and can 
be detected using a high frequency ultrasound. 
Studies have shown that optic nerve sheath 
diameter measurement has: 
• High sensitivity for ruling out raised intracranial 
pressure in a low-risk group 
• High specificity for ruling in raised intracranial 
pressure in a high-risk group.  
 
A 2011 study done in adult patients with 
different kinds of brain injury showed an optimal 
optic nerve sheath diameter for detection of 
intracranial hypertension (ICP > 20 mmHg) was 
≥0.48 cm with a sensitivity 96% and specificity 94%. 
Another study done in trauma patients with median 
Glasgow Coma Scale of 7 showed that the ability to 
detect intracranial hypertension was high for ONSD 
with area under the curve of 0.91. 
 
Steps: 
1. Perform a thorough clinical and neurological 
examination of the patient for increased 
intracranial pressure.  
2. A high frequency linear probe is used. 
 
The linear probe has a frequency of 5-7.5 MHz and is used to 
see fine detail at depths up to 6cm. See Introduction to 
Ultrasonography for more details. 
 
3. Patient is positioned supine; the eye is covered 
with the eyes shut with an occlusive dressing 
(such as Tegaderm®) or clean tape. Copious 
amounts of ultrasound gel are applied over the 
tape.  
 
An occlusive dressing is applied over the eye and generous 
ultrasound gel is then applied.  
 
4. The optic nerve sheath is located 3mm behind the 
globe. It appears as a bright (hyperechoic) 
circular or oval structure surrounding the dark 
(hypoechoic), longitudinal, optic nerve.  
With a gentle application of transducer on the 
globe, a characteristic image with the optic nerve 
and sheath emerging posteriorly should appear as 
shown below. 
5. The papilla is located as shown. A 3mm a line is 
drawn along the long axis of the nerve sheath  and 
marked as a distance Point A- A.  
6. A line perpendicular to the A-A is then drawn at 
the 3mm depth from the medial to the lateral 
inner walls of the hyperechoic nerve sheath and 
is marked as Point B -B, which is the Optic Nerve 
Sheath Diameter. 
Sonographic Assessment of Optic Nerve Sheath Diameter for Increased Intracranial Pressure 
Surafel Dubale, Yohannes Seife, Robel Beyene  
 
OPEN MANUAL OF SURGERY IN RESOURCE-LIMITED SETTINGS 
www.vumc.org/global-surgical-atlas 
This work is licensed under a Creative Commons Attribution-Share Alike 3.0 Unported License  
 
 
With the probe held in longitudinal orientation, (sagittal plane) 
a distance of 3mm from the inner wall of the nerve sheath (A-
A’) is first measured. Then, at this distance, the width of the 
nerve sheath (B-B’) is measured.  
 
7.  Measurement is done in both the longitudinal 
(sagittal) axis, as shown above, and the 
transverse (axial) axis, as shown below. The 
average is taken. The measurement is then 
repeated on the other eye and the average is taken 
as the mean Optic Nerve Sheath Diameter. 
 
With the probe oriented transversely (Axial plane) the 
measurement is repeated as above.  
 
Interpretation:  
 
Normal values are shown below. Values 
above these indicate elevations in intracranial 
pressure above 20mmHg. 
Up to 4 mm in infants 
Up to 4.5 mm in children 
Up to 5 mm in adults 
 
Pitfalls 
The following conditions can cause the optic nerve 
sheath diameter to be elevated without an increase in 
intracranial pressure:  
• Optic neuritis 
• Optic nerve glioma 
• Optic nerve meningioma 
• Inflammatory infiltration 
• Graves’ orbitopathy  
• Leukemic infiltration 
• Orbital congestion with sheath swelling 
• Obesity / high body mass index 
• Chronic ICP elevation 
 
 
Surafel Dubale, MD 
AIC Kijabe Hospital  
Kenya 
 
Yohannes Seife MD FCCM 
MedStar, Washington Hospital Center 
Washington, DC, USA 
 
Robel Beyene MD FACS 
Vanderbilt University Medical Center 
Nashville, TN, USA 
 
October 2023 
 
 
 
Sonographic Assessment of Optic Nerve Sheath Diameter for Increased Intracranial Pressure 
Surafel Dubale, Yohannes Seife, Robel Beyene  
 
OPEN MANUAL OF SURGERY IN RESOURCE-LIMITED SETTINGS 
www.vumc.org/global-surgical-atlas 
This work is licensed under a Creative Commons Attribution-Share Alike 3.0 Unported License  
 
Further Reading:  
Open Access: 
Ohle R, McIsaac SM, Woo MY, Perry JJ. 
Sonography of the Optic Nerve Sheath Diameter for 
Detection of Raised Intracranial Pressure Compared 
to Computed Tomography: A Systematic Review 
and Meta-analysis. J Ultrasound Med. 2015 
Jul;34(7):1285-94. 
doi: 10.7863/ultra.34.7.1285. 
 
Robba C, Cardim D, Tajsic T, Pietersen J, Bulman 
M, Donnelly J, Lavinio A, Gupta A, Menon DK, 
Hutchinson PJA, Czosnyka M. Ultrasound non-
invasive measurement of intracranial pressure in 
neurointensive care: A prospective observational 
study. PLoS Med. 2017 Jul 25;14(7):e1002356. doi: 
10.1371/journal.pmed.1002356.  
 
Not Open Access:  
Rajajee, V., Vanaman, M., Fletcher, J.J. et al. Optic 
Nerve Ultrasound for the Detection of Raised 
Intracranial Pressure. Neurocrit Care 15, 506–515 
(2011). 
https://doi.org/10.1007/s12028-011-9606-8 
 
