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Optic Nerve Sheath Diameter (ONSD) Measurement for Intracranial Pressure Monitoring
1. Optic Nerve Sheath Diameter (ONSD) Measurement
for Intracranial Pressure Monitoring
AdeWijaya, MD
August 2017
2. Outline
โข Intracranial Pressure
โข Etiology of Increase Intracranial Pressure
โข Intracranial Pressure Measurement
- Standard (invasive)
- Non-invasive
โข The Anatomy of Optic Nerve Sheath
โข ONSD Measurement
- Advantages vs Disadvantages
-Technique
โข Differential Diagnosis of increase ONSD
โข Summary
3. Intracranial Pressure (ICP)
Djordje Popovic, Michael Khoo and Stefan Lee. Non-invasive monitoring of intracranial pressure.
Recent Patents on Biomedical Engineering 2009, 2, 165-179
4. Increase Intracranial Pressure - Etiology
Djordje Popovic, Michael Khoo and Stefan Lee. Non-invasive monitoring of intracranial pressure.
Recent Patents on Biomedical Engineering 2009, 2, 165-179
7. The Anatomy of the Optic Nerve Sheath
Case courtesy of Dr Frank Gaillard, Radiopedia.org. From the case Optic nerve and chiasm (MRI anatomy).
8. ONSD Measurement
The first report of ultrasound imaging
of the eye was in 1956.
Common cut-off is 5 mm
Liu D, Kahn M. Measurement and relationship of subarachnoid pressure of the optic nerve to intracranial pressures
in fresh cadavers. Am J Ophthalmol. 1993;116(5):548โ556
Shevlin C. Optic Nerve Sheath Ultrasound for the Bedside Diagnosis of Intracranial Hypertension: Pitfalls and
Potential. Critical Care Horizons 2015; 1: 22-30.
9. ONSD Measurement
Advantages
โข reproducibility of measurements
โข the non-invasive nature of the technique
โข ready availability of equipment
โข portability of equipment
โข rapid performance
โข relatively low costs
โข avoidance of ionising radiation
โข avoidance of patient transport for imaging
Disadvantages
โข lack of a uniform cut-off value
โข operator dependent
โข potential risk of pressure injury to the globe
10. TheTechnique of Optic Nerve Sheath Ultrasound
โข Select the high frequency linear array probe.
โข Apply ultrasound gel liberally to the closed eyelid. If desired, a clear thin dressing (e.g.
IV cannula dressing) can be used as a barrier between the closed eyelid and the gel
medium although this is not strictly necessary.
โข Resting the probe hand on a bony structure such as the forehead or brow ridge
stabilises the image and lowers the risk of inadvertent pressure on the globe.
โข Place the ultrasound probe lightly over the gel in a transverse orientation initially.
There should neither be any direct contact of the probe with the eyelid nor pressure
exerted on the globe.The probe marker should be orientated laterally
โข With small, subtle movements scan from side to side (i.e. temporal to nasal), slowly
angling the probe superiorly or inferiorly to bring the optic nerve into view.The nerve
will appear as a โblack stripeโ running posteriorly from the rear of the globe.The goal is
to centre this on the monitor. If the lens or iris is not seen in your image, the imaging
plane is likely off-axis and may result in an underestimation of ONSD.
11. TheTechnique of Optic Nerve Sheath Ultrasound
โข The globe should also be scanned in the parasagittal plane, with the probe
marker superiorly, towards the patientโs forehead
โข Both eyes should be scanned, in case of unilateral papilloedema.
โข The time spent in active scanning should be minimised. Once the optimum
view has been obtained, store the image either as a frame or a video loop and
remove the probe from the eye. Measurements can then be performed without
unnecessary exposure of the eye to ultrasound energy.
โข Use the caliper function on the ultrasound to enable precise measurement.
First locate a point 3 mm posterior to the optic disk. At this point place the
calipers at 90 degrees to the axis of the optic nerve to measure the diameter of
optic nerve and optic nerve sheath
โข Take the average of two or three measurements for each side.
12. Differential Diagnosis
The differential diagnosis of increased ONSD includes:
โข raised intracranial pressure
โข optic neuritis
โข arachnoid cyst of the optic nerve
โข anterior orbital masses
โข cavernous sinus masses
โข trauma to the optic nerve
โข optic nerve sheath meningioma
13. Summary
โข ICP monitoring is important in treating neurologic patients with increase ICP
โข Standard monitoring measurement is invasive
โข Therefore, for alternatives, itโs developed some non-invasive methods
โข ONSD measurement using ultrasound is one of the non-invasive method
โข ONSD measurement advantages including readily available, low cost, rapid
performance, avoiding patients transport and minimal side effects.