Occurrence of physiologic gaze-evoked nystagmus at small angles of gaze.

PURPOSE: Physiologic gaze-evoked nystagmus (GEN) is one of many normal eye movements seen on the neurologic examination. GEN occurring at gaze angles >45 degrees is considered a positive sign in the Horizontal Gaze Nystagmus Test (HGNT) used by United States police officers to determine alcohol intoxication.

METHODS: 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 degrees intervals until they reached extreme gaze bilaterally. Eye movements were recorded using infrared video-oculography.

RESULTS: In addition to a high incidence of physiologic GEN at gaze angles 30 degrees and greater (at 30 degrees, n = 43%; at 40 degrees, n = 73%; at extreme gaze, n = 93%), the authors demonstrated that physiologic GEN occurs at smaller gaze angles (at 10 degrees, n = 21%; at 20 degrees, n = 34%).

CONCLUSIONS: A significant number of subjects with normal vision have physiologic GEN at gaze angles as small as 10 degrees. 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.