Answer: Cold caloric test
Cold caloric test (oculovestibular reflex) can rule out psychogenic coma or malingering with very high sensitivity and specificity. Irrigation of ear with 60-100mL of ice water can have 3 kinds of response
- A slow tonic deviation of the eye toward the ice happens in true coma with an intact brainstem.
- No response means damage to the brainstem
- Fast phase nystagmus away from the cold ear happens in an awake patient.