Neurootological Tests

VESTIBULAR SYSTEM

Caloric testing (vestibulo-ocular reflex)

Compensatory mechanisms may mask clinical evidence of vestibular damage - spontaneous and positional nystagmus. Caloric testing provides useful supplementary information and may reveal undetected vestibular dysfunction. Stimulus is maximaJ with the head

Method: Water at 30 C irrigated into the external auditory meatus. Nystagmus usually develops after a 20 second delay and lasts for more than a minute. The test is repeated after 5 minutes with water at 44°C.

Cold water effectively reduces the vestibular output from one side, creating an imbalance and producing eye drift towards the irrigated ear. Rapid corrective movements result in 'nystagmus' to the opposite ear. Hot water (44°) reverses the convection current, increases the vestibular output and changes the direction of nystagmus.

N.B. Ice water ensures a maximal stimulus when caloric testing for brain death or head injury prognostication.

Time from onset of irrigation to the cessation of nystagmus is plotted for each ear, at each temperature

Normal 3Q L ' response supported 30" from the horizontal (with the lateral semicircular canal in a vertical plane).

supported 30" from the horizontal (with the lateral semicircular canal in a vertical plane).

Right semicircular canals

Convection current induced in lateral semicircular canal

Vestibular nucleus

nuclei

VI nuclei

nuclei

VI nuclei

Fast

Damage to the labyrinth, vestibular nerve or nucleus results in one of two abnormal patterns, or a combination of both.

Canal paresis

Left canal paresis -1

Directional preponderance

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