HGN eye test in OWI

Updated: May 31

The horizontal gaze nystagmus, or, HGN, is one of three purportedly standardized field sobriety tests used in Iowa to build evidence to temporarily seize defendants, conduct searches of bodily samples, make OWI arrests, and win drunk driving convictions.

The HGN measures horizontal nystagmus, or horizontal “jerkiness” of the eyeball. The theory is that alcohol gaze nystagmus, or, AGN, is caused by alcohol interfering with the central nervous system including that which controls eye movement.

Defense lawyers look for contamination sources that can cause optokinetic nystagmus, or, a false positive—quick, jerky eye movement caused by fast moving lights or other objects. Test subjects should not face “blinking” lights including, for example, emergency top lights on patrol cars.

If you or a loved one has been arrested for OWI (DUI) in the State of Iowa, contact us. However, be advised that reading a blog is not a substitute for legal advice and that sending unsolicited information to a lawyer over the Internet does not establish an attorney-client relationship.

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