Optic nerve sheath diameter

Optic nerve sheath diameter has significance in the assessment of papilloedema in cases of elevated intracranial pressure.


The optic nerve sheath demonstrates changes in diameter with CSF 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 1.

Radiographic features

The measurements are taken at a distance of 3 mm from the globe (the site of maximum pressure changes) along the long axis of the optic nerve. These measurements can be performed on ultrasound using a linear array probe and on a T2W sequence on MRI. The intermodality difference in measurements is minimal and correlate well with CSF pressure changes ref.

  • normal optic nerve sheath diameter range is 4.8-5.8 mm
  • a value of >5.8 mm corresponds well with a raised CSF pressure of 25 mmHg indicating papilloedema due to intracranial hypertension
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Article information

rID: 58887
Section: Approach
Synonyms or Alternate Spellings:
  • ONSD

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