The Caloric Test: By the Numbers

Caloric irrigation is performed by irrigating the ear canal with either water or air for a period of 30 to 60 seconds. In order for the test to provide sensitive, accurate information, several minimum standards must be met.
1. The temperature of the air or water must be precisely 7 degrees Celsius over or under body temperature to compare to published norms. This requires a calibrated air or water irrigator.
2. The eye movements must be calibrated, recorded and analyzed. The eye movements generated from caloric irrigation are nystagmus, which typically have a fast phase and a slow phase. The slow phase is a sensitive indicator of labyrinthine responsiveness. Eye tracking is obtained through infrared cameras that track the darkest spot (the pupil) of the eye as it moves. The test must be performed in total darkness, and any visual target will suppress the labyrinthine response and render the test inaccurate.
3. Throughout the process, the examiner must maintain a steady consistent irrigation, assuring the patient does not move or tilt their head.
4. Once the irrigation is complete, the practitioner must continuously and simultaneously provide mental alerting tasks so nystagmus are not suppressed, and instruct the patient to keep their eyes open so nystagmus can be recorded accurately.
5. During the recording period, while nystagmus are still present, but after the peak response, the practitioner must introduce a visual fixation target.
6. After the recording period has ended and the nystagmus have ceased, the practitioner must analyze the data and manually remove random eye movements or artifacts that, in the judgment of the examiner, do not represent slow phase nystagmus.
7. Once the recording and analysis are complete, the patient is given sufficient time, usually five minutes, before the opposite ear can be irrigated with no significant chance of residual thermal effect from the previous irrigation.
8. The standard test protocol includes four irrigations, two per ear, with a stimulus both above and below body temperature. Once all four irrigations are completed and analyzed, a mathematical formula (known as Jonkees formula) is applied to the results, and an estimate of relative weakness between the two ears, and the relative difference between left beating and right beating nystagmus is completed.