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

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

Answer: (C)

Caloric testing uses temperature-induced convection currents in the horizontal semicircular canal to stimulate the vestibulo-ocular reflex. Warm irrigation on a side causes endolymph to rise and flow toward the ampulla on that same side, exciting the vestibular nerve there. This excitation is interpreted as head rotation toward that ear, so the quick phase of the nystagmus beats toward the irrigated side. Therefore, warming the right ear produces nystagmus with the fast component to the right. A handy reminder is COWS: warm equals same side, cold equals opposite. Downbeating would suggest a different mechanism or central involvement, not the horizontal canal response seen with caloric testing.