Spontaneous nystagmus and caloric nystagmus in cases of acute vestibular dysfunctions.

It is very difficult to know exact caloric responses when spontaneous nystagmus is very strong. A method of determining caloric response was tested in 42 cases of acute vestibular dysfunction with strong spontaneous nystagmus. Caloric nystagmus was evoked by 20 ml of water at 5°C and recorded by electronystagmography. Spontaneous nystagmus was also recorded with eye open in darkness. The slow phase velocities of spontaneous nystagmus and caloric nystagmus were calculated. When the spontaneous nystagmus was in the same direction as the caloric nystagmus, the caloric response of this ear was expressed by subtracting the slow phase velocity of spontaneous nystagmus from the slow phase velocity of caloric nystagmus. When the spontaneous nystagmus was evoked in the other direction, the caloric response of this ear was expressed by adding the slow phase velocities of caloric nystagmus and spontaneous nystagmus.Caloric tests should be performed frequently to determine the exact responses because of quick changes of spontaneous nystagmus and lesions.