Clinical question Does my patient have elevated ICP?
Patient positioning Supine
Supplies needed Small tegaderm (to avoid ultrasound gel irritating the cornea)
Probe Linear
Normal findings The upper limit of normal optic nerve sheath diameter: 4 mm in infants.
5 mm in children.
5 mm in adults.
Sensitivity & specificity A meta-analysis of 12 studies showed a sensitivity of 95.6% and specificity of 92.3%
Contraindications Open globe injury, periorbital swelling or hematoma, ocular trauma, history of glaucoma
Alternate diagnostic modalities Fundoscopy, non-contrast CT scan

How to perform this exam

  1. Prepare your supplies: obtain an ultrasound machine with a linear probe, tegaderm & ultrasound gel
  2. If patient is conscious, explain the purpose of the exam and that it is painless and without radiation.
  3. Position your patient for comfort - supine with head flat.
  4. Apply small tegaderm to the optic globe.
  5. Apply copious ultrasound gel to anterior surface of tegaderm.
  6. Select linear probe on ultrasound machine.
  7. If your exam has an exam setting for optic ultrasound, select it; otherwise, select small parts.
  8. Apply minimal pressure to avoid injury to the eye. Placing your hypothenar eminence on the patients cheek/face for stability can help eliminate pressure on the eye.
  9. Take measurements in sagittal & axial planes and average these for a more accurate measure of optic nerve sheath diameter.
  10. You can ask the patient to look up, down, or in either direction to improve your view of the optic nerve.
  11. Compare measurement of contralateral eye.

Relevant Anatomy

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Note that the optic nerve diameter is being measured ~3mm from the retina.

ONSU Views.jpg

Axial & Sagittal (incorrectly labeled coronal above) views of the optic nerve sheath shown here