DUI/DWI Horizontal Gaze Nystagmus Test

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hgn.bmpHorizontal gaze nystagmus is usually the first test administered when a driver is suspected of drinking and driving. Nystagmus is defined as an involuntary jerking of the eyes. Nystagmus is always present, to some degree, but it is far more noticeable when an individual has alcohol in his or her system. In order to administer the HGN test correctly, an officer must have the suspect stand with legs together and arms at the side. The officer should instruct the person to remove eyeglasses and inquire whether the person has contact lenses, a head injury or eye problems. The suspect must be instructed to follow the stimulus with their eyes only, keeping their head still. The stimulus is placed 12-15 inches in front of the person's face, and is moved back and forth in a number of passes. The first pass is to assess if the individual's eyes are tracking equally. The officer also holds the stimulus still to determine that both pupils are the same size. If the subject dose not show equal tracking or has differing pupil sizes there could be a medical problem.

The officer then moves the stimulus in a series of twelve passes. During the first four passes, taking about two seconds out and two seconds back, the officer determines if there is smooth pursuit, checking each eye twice. The officer will then move the stimulus to the far side of each eye, so that no white is showing, and holds it there for at least four seconds. At this point the officer is checking for distinct and sustained nystagmus at maximum deviation. Finally, the officer will check for the onset of nystagmus prior to 45 degrees. To accomplish this the officer will slowly move the stimulus outward from the center of the subject's face until nystagmus is observed, and then holds the position long enough to confirm its existence. All three components should be done four times, twice on each eye. When Maryland Courts consider the weight of the HGN tests they require that the officer administering the test is properly trained and certified. Assuming that the officer is qualified as an expert and administered the test properly, the HGN is limited to only be indicative of showing the presence of alcohol and cannot be used to show impairment. In fact, nystagmus has countless other causes which make the test inherently unreliable. An experience Maryland DUI lawyer must make the Court aware of all of these considerations when representing and individual accused of drinking and driving in Maryland.

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