1. 視刺激検査

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  • 堤 剛
    東京医科歯科大学耳鼻咽喉科

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  • Visually stimulating examination

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<p>　As visually stimulating examination, outline of gaze-evoked nystagmus, rebound nystagmus, saccade, smooth pursuit and optokinetic examination were provided We provide an outline of the responses in optokinetic nystagmus testing, including gaze-evoked nystagmus, rebound nystagmus, saccade, and smooth pursuit. The history and underlying physiology, the comprehensive testing procedure and representative findings are described.</p><p></p><p>　In Japan,“gaze-nystagmus” refers to gaze-evoked nystagmus and spontaneous nystagmus under eye fixation; the former is caused mainly by damage of the paramedian pontine reticular formation, and the latter by imbalance of peripheral vestibular function. Rebound nystagmus includes directional alternation of gaze-evoked nystagmus during lateral fixation, and also alternation immediately after change of the gaze direction from lateral to forward. Congenital nystagmus is also characterized by bi-directional gaze-evoked nystagmus, although sometimes it takes the form of pendular nystagmus. Opsoclonus and ocular flutter manifest as bi-directional saccade movements without inter-saccadic intervals, caused by cerebellar disinhibition of neuronal bursts. On the other hand, square-wave jerks are characterized by saccadic intrusions with inter-saccadic intervals of about 200-400ms.</p><p></p><p>　Saccadic ocular movements are controlled by neuronal bursts, which are integrated at the neural integrator, to maintain lateral gaze. Omnipause neurons continuously inhibit this neuron bursting, and loss of this inhibition causes saccade movements. This system is controlled through the superior colliculus. Dysmetria of saccade movements is caused by cerebellar deficit.</p><p></p><p></p><p>　Smooth tracking movements are used to fix the images of moving objects on the fovea. Velocity information for such tracking is delivered through the medial vestibular nucleus and nucleus prepositus hypoglossi, which receive neural projections from the cerebellar flocculus. Cerebellar dysfunction causes saccadic pursuit, which is considered as being attributable to decreased gain of pursuit and consequent catch-up saccade.</p><p></p><p>　Accelerating head movements trigger the vestibulo-ocular reflex, which fixate one's visual line on an object. However, uniform head motion cannot trigger the vestibulo-ocular reflex, and requires another system; in this case, it is achieved by pursuit and optokinetic eye movements. The optokinetic reflex is disturbed by cerebellar deficit, which causes decreased gain of the optokinetic reflex and consequent catch-up saccade. Congenital nystagmus may also manifest as saccadic optokinetic nystagmus, which exhibits directional “inversion.”</p>

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