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R. M. Williams, S. B. Stevenson, J. M. Wensveen, S. J. Rubenzer; Normative Data on Maximum Angle of Abduction and Nystagmus Onset Angle. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2827.
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© ARVO (1962-2015); The Authors (2016-present)
Horizontal Gaze Nystagmus is assessed by law enforcement as one part of the Standardized Field Sobriety Test, where nystagmus that occurs at gaze angles less than 45 degrees increases suspicion of intoxication, though little normative data have been reported on gaze evoked nystagmus, or on the role of factors such as fatigue. We measured the maximum angle of abduction and the angle of onset of nystagmus in 103 sober individuals, and looked for fatigue effects in 4 subjects.
Subjects were seated with head stabilized and positioned so that the left eye was directly over the pivot of a rotating arm carrying a camera, infrared LED source, and a small mirror. The camera provided experimenters with a magnified view of the eye that stayed on axis with gaze direction as the arm rotated. The arm was moved in 5 degree increments, and gaze stability and accuracy were assessed at each position. Nystagmus onset was recorded as the smallest angle at which distinct nystagmus of at least 3 beats was noted. Maximum deviation was recorded as the largest angle for which the target remained centered in the pupil image. For the large sample, measurements were made on optometry students during a morning laboratory exercise. For the fatigue study, repeated measures were made on both eyes of 4 subjects at 3 different times of day spanning a 12 hour period. Measurements were repeated on 5 days.
The maximum angle of abduction varied from 35 to 65 degrees, with mean of 48 +/- 5.9 degrees. Nystagmus occurred in 70/103 subjects, with a mean angle of onset 44 +/- 6.0 degrees. For 28/103 subjects the angle of onset was the same as the maximum deviation. The fatigue study showed that both measures increased slightly with time of day but the effect was not significant (repeated measures ANOVA, df 3, 2, F 1.952, p 0.2449).
End gaze nystagmus is a common finding in the general population, suggesting that the roadside HGN test may suffer from a high false positive rate. 70 of 103 subjects showed nystagmus at max deviation, and half of our sample showed nystagmus at or before 45 degrees. Fatigue did not have a significant effect on the occurrence or magnitude of nystagmus in our sample.
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