To examine the discovery and evolution of the caloric response test (CRT) and explore why ice water is more commonly used than warm water.

The CRT is generally associated with assessment of the brainstem during the BD/DNC evaluation, but it can also be used to localize vertigo or hearing loss.

We reviewed the literature to explore the history of the CRT.

The CRT was developed by Dr. Robert Bárány in 1914 after he observed nystagmus in patients with ear infections treated with ear irrigation. Lower water temperatures (defined as ice water at 0°C or cold water at 7°C below body temperature) caused slow phase nystagmus towards the irrigated ear while warm water (defined as 7°C above body temperature) caused nystagmus away from it. Bush et al. subsequently found that use of warm water was more specific for confirmation of a unilateral peripheral vestibulocochlear lesion, but Barros and Caovilla found that cold 30°C water produced a more prominent nystagmus that was easier to visualize. The ice water CRT was included in the Harvard Medical School description of BD/DNC evaluation in 1968. It has since been included in BD/DNC evaluation guidelines around the world, including the AAN guidelines. We postulate that ice water was chosen over cold or warm water due to its ability to produce a more prominent nystagmus (to avoid result ambiguity), ease of preparation compared to precisely heated or cooled water, and avoidance of thermal injury risk associated with hot water.

The CRT can be used to evaluate vestibulocochlear function to localize peripheral versus central nervous system pathology, but its most common use is in BD/DNC evaluation. The standardization of ice water use over other temperatures is likely based on ability to identify the nystagmus response, prepare the water, and prevent thermal injury risk.