Prevalence of positional nystagmus during static positional testing in normal healthy population using video-nystagmography.
University of Southampton, Institute of Sound and Vibration Research,
Positional nystagmus (PN) is a type of nystagmus that occurs as a result of the head or the head and body being moved from one position to another and then statically maintained in the critical position. Until recently, PN was always considered as an abnormal finding regardless of its character. However, with emergence of the highly sensitive technique of videonystagmography (VNG) it has become apparent that PN does occur frequently in healthy individuals. Since the present criteria for determining pathological PN have been based on electronystagmography (ENG), which provides less sensitive measure of vertical eye movements than VNG, there have been attempts to outline new criteria based on the VNG method. However, to date, no new explicit criteria have been agreed on by scientists. Further to this, a number of factors have been found to affect results of static position testing, including mental alerting, response repeatability, and the number of head and body positions tested, and these factors all need to be examined.
Apart from investigating prevalence of PN in healthy normal individuals, this experiment examined three variables: the effects of mental alerting, within session repeatability of PN, and the prevalence of PN across different head and body positions. Eighteen participants (13 female, 5 male) aged 22 to 76 years with no history of balance disorder were tested in four identical sets of static positional testing using VNG. Each test set included 11 head and body positions. Two of these test sets were conducted with mental alerting and two sets without mental alerting. Gathered data were analysed with respect to presence of PN, direction of PN, and peak slow phase velocity (SPV).
In total 66.7% of the participants developed persistent PN in at least one test position in at least one of the four test sets. Three main types of PN were found in this study: vertical, horizontal, and oblique. The most common type of PN across the entire study was vertical up-beating (VUB) PN (45.6%); however, the most common type of PN across individual participants was horizontal PN (75%). Oblique PN had the greatest mean peak SPV. Mental alerting had significant effect on prevalence of PN, but it did not increase the magnitude of the SPV. The prevalence of PN was only modestly repeatable within the paired mental alerting and non-mental alerting test sets, and the repeatability was greater for the test sets with mental alerting. There were no significant differences between the SPV magnitudes within the paired test sets, suggesting good within-session repeatability of the SPV magnitudes. The „supine with head straight‟ (SHS) and „supine with head turned right‟ (SHR) positions provoked the highest rates of PN; however, there was no one position that would not provoke PN in at least one participant and at least one test set.
Overall 22.2% of the participants did not fit the current criteria for „normality‟ based on ENG, indicating the need for refinement of those criteria using VNG.
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