Horizontal Gaze Nystagmus (HGN Test)

One of the purposes of allowing cross examination of witnesses is the idea of confronting your accuser. The theory is that the credibility and sincerity of a witness accusing you is best tested by live cross examination.

A few days ago, while sitting in court waiting for my client’s driver’s license suspension hearing to start, I

Nystagmus is an actual medical phenomenon that describes an involuntary eye movement, or ‘ a jerking of the eyes’, as police officers often call it. Nystagmus can be difficult to detect, and has multiple causes, other than alcohol consumption.

Unfortunately, diagnosing both the complex medical condition itself, as well as divining its cause, has been boiled

In Chapter 8 of NHTSA’s “DWI Detection and Standardized Field Sobriety Testing” Manual is a subsection entitled “Overview of Nystagmus”:

Nystagmus is defined as an involuntary jerking of the eyes. Alcohol and certain other drugs cause Horizontal Gaze Nystagmus.

Categories of Nystagmus

There are three general categories of nystagmus:

1. Vestibular Nystagmus is caused by movement

Vestibular Nystagmus is caused by movement or action to the vestibular system.

A. Types of vestibular nystagmus:

Rotational Nystagmus occurs when the person is spun around or rotated rapidly, causing the inner fluid in the ear to be disturbed. If it were possible to observe the eyes of a rotating person, they would be seen to

Nystagmus can result directly from neural activity:

Optokinetic Nystagmus occurs when the eyes fixate on an object that suddenly moves out of sight, or when the eyes watch sharply contrasting moving images. 

Examples of optokinetic nystagmus include watching strobe lights, or rapidly moving traffic in close proximity. The Horizontal Gaze Nystagmus test will not be influenced