Diagnosis of vestibular imbalance in the blink of an eye.

BACKGROUND: In a recent study, the authors found that blinks in healthy volunteers always triggered ocular torsion quick phases during dynamic roll movements of the head. On the basis of this observation, they hypothesized that blinks in patients with a vestibular tone imbalance would also trigger torsional quick phases. METHODS: Using video-oculography with a fixation target, the authors recorded the ocular torsion position of the left eye of 37 participants while they made voluntary blinks once every 6 to 10 seconds. The participants were recruited from four groups: two age groups of healthy volunteers with a mean +/- SD age of 32 +/- 4 (n = 9) and 65 +/- 11 y (n = 9); patients with a unilateral vestibular disorder in an acute state (n = 12, 53 +/- 17 y); and those in a persisting state in which spontaneous nystagmus had already faded (n = 9, 65 +/- 13 y). RESULTS: In the control groups of healthy volunteers, blinks triggered no or only small quick phases on the order of 0.1 deg. In both patient groups blinks always triggered quick phases with significantly higher amplitudes of 1.85 +/- 1.02 deg and were followed by exponentially decaying slow-phases with time constants on the order of 1 to 2 seconds. Patients in the persisting state clearly differed from patients in the acute state in that their torsional spontaneous nystagmus had already vanished due to vestibular compensation. But surprisingly, these two groups did not show a large difference in terms of the effect of blinks on ocular torsion. The authors always observed torsional quick phases with the upper pole of the eye beating away from the side of the lesion. CONCLUSIONS: Blinks are able to trigger torsional quick phases in patients with both acute and persisting vestibular disorders. The side of the impairment can be determined from the direction in which the eye is rotated after a blink. Thus, ocular torsion recordings during blinks can be used as a simple clinical test for a vestibular tone imbalance, particularly during a persisting failure in which spontaneous nystagmus has resolved and can therefore no longer be used for diagnosis.

Autoradiographic measurement of regional brainstem blood flow: occlusion of the anterior inferior cerebellar artery.

Autoradiography was used to measure regional brainstem blood flow in Wistar rats following permanent left anterior inferior cerebellar artery (AICA) occlusion. With the AICA occluded, blood flow to the left vestibular nucleus decreased 31% while flow to the left cochlear nucleus decreased 47% when compared to the right (unobstructed) side. In the rat, the median pontine branch of the basilar artery was found to provide the principal blood supply to the vestibular nucleus. Electrocochleography was also used to measure the action potential (AP), summating potential (SP) and cochlear microphonics (CM) during left AICA occlusion. The AP disappeared completely after at least 7 min, while the SP polarity changed from negative to positive. Findings also showed that CM2 did not disappear completely in pre-mortem animals.