How is nystagmus characterized in benign paroxysmal positional vertigo (BPPV)?

Updated: Feb 15, 2018
  • Author: John C Li, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Answer

Because the type of BPPV is defined by the distinguishing type of nystagmus, defining and explaining the characterizing nystagmus are also important.

Nystagmus is defined as involuntary eye movements usually triggered by inner ear stimulation. It usually begins as a slow pursuit movement followed by a fast, rapid resetting phase. Nystagmus is named by the direction of the fast phase. Thus, nystagmus may be termed right beating, left beating, up-beating (collectively horizontal), down-beating (vertical), or direction changing.

If the movements are not purely horizontal or vertical, the nystagmus may be deemed rotational. In rotational nystagmus, the terminology becomes a bit more loose or unconventional. Terms such as clockwise and counterclockwise seem useful until discrepancies regarding point of view arise: clockwise to the patient is counterclockwise to the observer. Right versus left terminology is poorly descriptive because as the top half of the eye rotates right, the bottom half moves left.

Rotational nystagmus also can be described as geotropic and ageotropic. Geotropic means "toward earth" and refers to the upper half of the eye. Ageotropic refers to the opposite movement. If the head is turned to the right, and the eye rotation is clockwise from the patient's point of view (top half turns to the right and toward the ground), then the nystagmus is geotropic. If the head is turned toward the left, then geotropic nystagmus is a counterclockwise rotation. This term is particularly useful in describing BPPV nystagmus because the word geotropic remains appropriate whether the right or the left side is involved.

These 2 terms are useful only when the head is turned. If the patient is supine and looking straight up, these terms cannot be used. Fortunately, the nystagmus associated with BPPV usually is provoked with the head turned to one side. The most accurate way to define nystagmus is by terming it clockwise or counterclockwise from the patient's point of view.


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