Horizontal Gaze Nystagmus (HGN)

The horizontal gaze nystagmus test is one of three field sobriety tests that comprise the standardized field sobriety test (SFST) battery (the other two tests are the walk-and-turn test and the one-leg-stand test).

Nystagmus is an involuntary jerking or bouncing of the eyeball that occurs when there is a disturbance of the vestibular (inner ear) system or the oculomotor control of the eye. Horizontal gaze nystagmus (HGN) refers to a lateral or horizontal jerking when the eye gazes to the side. In the impaired driving context, alcohol consumption or consumption of certain other central nervous system depressants, inhalants or phencyclidine, hinders the ability of the brain to correctly control eye muscles, therefore causing the jerk or bounce associated with HGN.

Nystagmus Caused by Non-Alcohol Related Disturbance of the Vestibular System

Rotational nystagmus is caused by a disturbance in the inner ear fluid when a person spins around. The nystagmus lasts only as long as the person is being spun. If an observer could see a person’s eyes while that person was spinning, a distinct jerking of the eye would be evident. Post-rotational nystagmus occurs after the person stops spinning. The nystagmus lasts for several seconds and can easily be seen.

Caloric nystagmus is caused by the movement of the inner ear fluid due to a difference in temperature of the fluid between the left and right ear. One way this can occur is if warm water is poured in one ear and cold water is poured in the other. Obviously this is an implausible scenario at roadside.

Nystagmus Caused by Neural Activity

Some types of nystagmus are caused by neural or muscle activity. Optokinetic nystagmus occurs when the eyes fixate on an object that moves quickly out of sight or passes quickly through the field of vision, such as occurs when a subject watches utility poles pass by while in a moving car. Optokinetic nystagmus also occurs when the eyes watch an object displaying contrasting moving images, such as black and white spokes on a spinning wheel. In either case, because the nystagmus is caused by the eye trying to catch up with the moving object, it lasts only as long as it takes for the object to stop moving, for the object to pass out of the field of vision, or for the eye to catch up to the object. Epileptic nystagmus is also a jerk nystagmus caused by neural activity that occurs primarily during epileptic or other types of seizures.

In addition, some people will exhibit a slight eye tremor when the eye moves to maximum deviation. This tremor is due mostly to eye strain rather than to any type of alcohol impairment or medical condition. When the HGN test is administered properly, a law enforcement officer cannot confuse this eye tremor with HGN due to alcohol impairment for several reasons. First, the eye tremor lasts only briefly and law enforcement officers are taught to hold the eye at maximum deviation for at least four seconds to ensure that the jerking is sustained. Second, the officer is looking for a distinct nystagmus, not a slight eye tremor. And finally, distinct nystagmus at maximum deviation is only one clue among the three the officer is looking for when checking for HGN.

Nystagmus Due to Pathological Disorders

Nystagmus may occur in people with brain damage, brain tumors or inner ear diseases. These disorders and others like them occur in a small number of the general population and even less often in drivers. Many of these alternative causes are so severe that it is unlikely that persons afflicted with the disorders would be driving, would not know they have the disorder or would be unaware of the effect the disorder has on their body. In addition, these types of nystagmus may be pendular rather than jerk nystagmus.

Even if your performance on the HGN is poor you still have many defenses available to win your case. Without an experienced DUI/DWI defense team fighting for you, you are in an unfair fight. You should act fast and act decisively.

Make an Appointment With the Law Offices of Guerami. Contact us today to speak with an experienced Maryland lawyer regarding an arrest for DUI/DWI. We offer free consultations that are always confidential

There exist several non-alcohol related types of nystagmus caused by neural or muscle activity. These other types are due to a variety of causes, such as other vestibular system (inner ear) and nervous system disturbances and pathological disorders. Many times defendants will suggest that the nystagmus the law enforcement officer saw was actually caused by something other than alcohol or other drugs. However, a properly trained law enforcement officer will not mistake other types of nystagmus, natural or otherwise, with HGN when taking into account all of the facts that contribute to the arrest decision.