Comparison of assessment of caloric nystagmus by observation of duration and by electronystagmographic measurement of slow-phase velocity.

The 'duration' of induced nystagmus was the first parameter used to quantify vestibular function during caloric testing. However, later work suggested that there was a poor correlation between this measure and the physiological events occurring during caloric testing. This, coupled with the development of electronystagmography and the value of a permanent record of the caloric responses, led to the widespread use of the 'slow-phase velocity' measurement of induced nystagmus, as the most commonly used parameter for assessment of the caloric test. Despite a wealth of literature, the 'best' parameter for measuring vestibular function using the caloric test remains undefined and the duration and slow-phase velocity parameters appear to provide different information. The strengths and shortcomings of these two parameters and their relative values are reviewed.