In caloric testing, cold water poured into the right ear produces which direction of nystagmus?

• A. Right beating
• B. Left beating
• C. No nystagmus
• D. Upbeating

Answer: (B)

In caloric testing, temperature differences in the ear create convection currents in the endolymph of the horizontal semicircular canal, which drives the vestibulo-ocular reflex and produces a fast-phase eye movement, i.e., nystagmus. The direction of the fast phase is summarized by COWS: Cold Opposite, Warm Same.

So, cooling the right ear makes the nystagmus beat to the left. The cold irrigation causes endolymph flow that reduces neural firing on the irrigated (right) side, which the brain interprets as head movement to the left. The brain then drives the eyes with a slow phase toward the right and a fast phase to the left, resulting in left-beating nystagmus.