This prospective observational study aimed to evaluate the differences between optic nerve sheath diameter (ONSD) between the patients’ two eyes and different ultrasound planes (transverse and sagittal). Participants were recruited over a two-year period from a single neurosurgical department. To be eligible for inclusion the patients needed to be aged over 14 years old and have a Glasgow coma scale score less than 12. Any known ophthalmic disease or optic nerve trauma was excluded. Details of how the ONSD was assessed using ultrasound are outlined. The means of the sagittal and transverse planes were recorded. Intracranial pressure (ICP) was measured using two invasive methods. A total of 50 participants were included in the study, with 164 ONSD ultrasound measurements of which 78 were performed at 30° supine position. There were various acquired brain injuries including haemorrhage, aneurysm, trauma, plus others. A statistical difference was found between transverse versus sagittal places for ONSD measurement (p=0.003) however, no significant difference was reported for right versus left eyes. There was also no significant difference between measurements for supine versus 30° supine. Correlation between ONSD and ICP improved using sagittal plane measurement. The authors outline the sensitivity and specificity of a variety of cut-offs for ONSD. It is acknowledged that ultrasound is a highly variable measurement method due to reliance on operator skill. Limitations of the study are highlighted including the results being relevant to patients with increased ICP, lack of age-matched healthy controls and no stratification analysis to account for the wide age range. The authors conclude that sagittal plane measurement is superior and uniocular measurement is sufficient.
What plane should be used for ultrasound measurement of the optic nerve sheath diameter?
Reviewed by Lauren Hepworth
The effect of different optic nerve sheath diameter measurements using ultrasound to assess intracranial pressure in patients with acute brain injury.
CONTRIBUTOR
Lauren R Hepworth
University of Liverpool; Honorary Stroke Specialist Clinical Orthoptist, Northern Care Alliance NHS Foundation Trust; St Helen’s and Knowsley NHS Foundation Trust, UK.
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