title: Observer variation in the sonographic measurement of optic nerve sheath diameter in normal adults.
abstract: OBJECTIVE
  To quantify the observer variation in the sonographic measurement of optic nerve sheath diameter (ONSD) in normal adults.
  
  
  METHODS
  Sixty-seven normal adult volunteers underwent ultrasound examination of each eye by three independent observers using a 7 MHz sector probe. Three measurements were made of each eye by each observer and a mean value calculated for each eye. Median and 5th-95th centile values for both intra- and inter-observer variation were calculated for the three observers.
  
  
  RESULTS
  The median intra-observer variation was +/-0.1 mm, with 5th-95th centile values of +/-0-0.4 mm. The median inter-observer variation was +/-0.2-0.3 mm, with 5th-95th centile values of +/-0-0.7 mm. Careful review of examination technique by the three observers after the first 17 examinations was shown to reduce both intra- and inter-observer variation.
  
  
  CONCLUSIONS
  The sonographic measurement of ONSD is a readily learned, reproducible technique with low intra- and inter-observer variation. The average inter-observer variation (+/-0.2 mm) is comparable to the inherent variability of the ultrasound machine. The importance of standardisation of examination technique is stressed.
authors.affiliation: Department of Radiology and Clinical Physics, Royal Hospital for Sick Children, G46 7PD, Glasgow, UK. s.ballantyne@virgin.net
authors.forename: S A
authors.initials: SA
authors.lastname: Ballantyne
authors.forename: G
authors.initials: G
authors.lastname: O'Neill
authors.forename: R
authors.initials: R
authors.lastname: Hamilton
authors.forename: A S
authors.initials: AS
authors.lastname: Hollman
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009186:Myelin Sheath / Q000000981:diagnostic imaging / Q000473:pathology; D015588:Observer Variation; D009900:Optic Nerve / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D015203:Reproducibility of Results; D014463:Ultrasonography