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Optokinetic Nystagmus
Optokinetic nystagmus (also called opticokinetic nystagmus) occurs when an image moves across the retina. It is a rhythmic to and fro movement of the eyes with a fast and slow phase that is identical to the nystagmus evoked by stimulation of hair cells in the semicircular canals. For example, as the visual scene moves from right to left across the retina, both eyes are driven slowly to the left to maintain the image of the visual target on the fovea of the retina. When the eyes reach the limit of their left lateral gaze, they shift rapidly back to the right to capture another target for foveation and, because the target is moving to the left, the slow movement to the left begins again. This cycle repeats rhythmically. The occurrence of optokinetic nystagmus confounds the observation of vestibular-evoked nystagmus at the beginning of a rotation. Optokinetic nystagmus is a normal response and can easily be elicited by having an individual observe a horizontally moving pattern of vertical black and white stripes.
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