7The Vestibular Audiogram II: VEMP, Otoliths and Function Tests

TcVEMP: the saccular probe

The cervical VEMP gives a quantitative measure of saccular function via the vestibulo-collic reflex carried by the inferior vestibular nerve, and is testable soon after birth An intact VEMP is strong evidence of an intact saccule and aids ear selection, for example choosing an ear in CHARGE association cVEMP rests on the click-evoked vestibulocollic reflex first described as a myogenic potential, and an absent VEMP is nonspecific.[2005][1994]

CoVEMP, head-heave and special signs

The ocular VEMP reflects utricular function through the vestibulo-ocular reflex A 'head heave' (transient interaural linear acceleration) quantifies utricular/translational-VOR function but is not yet widely used Increased-amplitude VEMP at subnormal stimulus levels suggests superior canal dehiscence or enlarged vestibular aqueduct.[2005][2001]

TFunctional and balance tests

The Sensory Organization Test (computerized posturography) and the Dynamic Visual Acuity test assess overall balance and VOR function Subjective visual vertical and posturography capture the integrated postural output rather than a single end organ These functional measures complement the end-organ-specific tests of the battery.[1994][2004]

CMapping tests to end organs

Caloric, rotary chair and vHIT probe the semicircular canals and the VOR; cVEMP probes the saccule and the vestibulo-collic reflex; oVEMP probes the utricle A complete work-up must include otolith testing because post-implant saccular injury — the commonest histopathological lesion — is otherwise missed cVEMP is the most sensitive marker of CI-induced vestibular injury, and a normal vHIT does not exclude meaningful otolith loss.[2005][2002]