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Chad A. Whyte, Anne Marie Petrock, Michael Rosenberg; Occurrence of Physiologic Gaze-Evoked Nystagmus at Small Angles of Gaze. Invest. Ophthalmol. Vis. Sci. 2010;51(5):2476-2478. doi: 10.1167/iovs.08-3241.
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Physiologic gaze-evoked nystagmus (GEN) is one of many normal eye movements seen on the neurologic examination. GEN occurring at gaze angles >45° is considered a positive sign in the Horizontal Gaze Nystagmus Test (HGNT) used by United States police officers to determine alcohol intoxication.
The authors enrolled 56 subjects after a brief survey and a neurologic examination yielding normal results. Subjects were directed to look at small targets on the wall in primary gaze and at 10° intervals until they reached extreme gaze bilaterally. Eye movements were recorded using infrared video-oculography.
In addition to a high incidence of physiologic GEN at gaze angles 30° and greater (at 30°, n = 43%; at 40°, n = 73%; at extreme gaze, n = 93%), the authors demonstrated that physiologic GEN occurs at smaller gaze angles (at 10°, n = 21%; at 20°, n = 34%).
A significant number of subjects with normal vision have physiologic GEN at gaze angles as small as 10°. This could potentially refute the “failing” grade that is the hallmark of the HGNT and propagates further testing of the validity of this test in the conviction of intoxicated drivers.
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