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Observer variation in the sonographic measurement of optic nerve sheath diameter in normal adults
S A Ballantyne1, G O'Neill, R Hamilton
1Department of Radiology and Clinical Physics, Royal Hospital for Sick Children, G46 7PD, Glasgow, UK. s.ballantyne@virgin.net
Aim:
To quantify the observer variation in the sonographic measurement of optic nerve sheath diameter (ONSD) in normal adults.
Materials And 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.
Conclusion:
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.
