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What is Horizontal Gaze Nystagmus and How Does It Affect My New Hampshire DWI Case?

The “Horizontal Gaze Nystagmus” (HGN) test is one of the three standardized NH field sobriety tests that a police officer might give to a driver, if the officer suspects the driver is driving under the influence of alcohol. HGN occurs when the eyes jerk involuntarily from left to right when trying to see something that is traveling sideways out of the field of vision.

Many factors can cause horizontal gaze nystagmus. For instance, medical conditions such as a concussion or neurological disorders will cause HGN. Some prescription medications will also increase the chances of its occurrence, whether or not the person taking the medication is fully capable of driving a car. Finally, horizontal gaze nystagmus will occur even in healthy people if they are facing a strobe light or other rapidly flashing light or object.

In order to determine whether HGN is the result of alcohol intoxication or another medical condition, NH police officers are trained to check for equal pupil sizes and whether the eyes can “track” the same object together before administering the test. However, since so many factors other than intoxication can cause or aggravate the condition, even a carefully-given test cannot conclusively prove that a driver is too drunk to drive.

If you’ve been charged with drunk driving in New Hampshire, an aggressive defense from an experienced New Hampshire DWI attorney can be valuable as you seek the best possible outcome in your case. At Tenn And Tenn, P.A., we have the legal resources and experience to fight for our clients’ rights to obtain the best possible outcome. For a confidential case evaluation, call Tenn And Tenn, P.A. today at 1-888-511-1010.