Alcohol Gaze Nystagmus

Gaze nystagmus refers to the involuntary "twitching of the eye when focused fixedly upon an object." Because alcohol slows the central nervous system, drivers who are intoxicated will experience an alcohol gaze nystagmus or a jerking of the eye at a lesser angle than a sober driver. Police use the Horizontal Nystagmus Test (HGN) when they are performing the standardized field sobriety test (FST) to determine if a driver is under the influence of alcohol.

Under the HGN test the police officer has the driver follow a stimulus, generally a small flashlight, with their eyes from left to right. The officer is evaluating the angle at which the pupil starts to exhibit nystagmus. Drivers who display nystagmus at or before a 45-degree angle are more likely to have a high blood alcohol concentration (BAC).

According to the National Highway Traffic Safety Administration (NHTSA), the HGN is supposed to be 77% reliable in determining whether a driver has a blood alcohol concentration above 0.10%. Talk to a DUI lawyer if you have been arrested for DUI and the police officer has evidence you failed the field sobriety test.