Types of Nystagmus: 2006 NHTSA Manual

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 or action to the vestibular system.

2. Nystagmus can also result directly from neural activity.

3. Nystagmus may also be caused by certain pathological disorders

Vestibular Nystagmus: NHTSA Manual 2006

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 jerk noticeably.

Post Rotational Nystagmus is closely related to rotational nystagmus: when the person stops spinning, the fluid in the inner ear remains disturbed for a period of time, and the eyes continue to jerk.

Caloric Nystagmus occurs when fluid motion in the canals of the vestibular system is stimulated by temperature as by putting warm water in one ear and cold in the other.

Positional Alcohol Nystagmus (PAN) occurs when a foreign fluid, such as alcohol, that alters the specific gravity of the blood is in unequal concentrations in the blood and the vestibular system.

Nystagmus Resulting from Neural Activity: NHTSA Manual 2006

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 by optokinetic nystagmus when administered properly.

Physiological Nystagmus is a natural nystagmus that keeps the sensory cells of the eyes from tiring. It is the most common type of nystagmus. It happens all the time, to all of us. This type of nystagmus produces extremely minor tremors or jerks of the eyes. These tremors are generally too small to be seen with the naked eye. Physiological nystagmus will have no impact on our (NHTSA) Standardized Field Sobriety Tests, because its tremors are generally invisible.

Gaze Nystagmus occurs as the eyes move from the center position. Gaze nystagmus is separated into three types:

(1) Horizontal Gaze Nystagmus occurs as the eyes move to the side. It is the observation of the eyes for Horizontal Gaze Nystagmus that provides the forst and most accurate test in the Standardized Field Sobriety Test battery. Although this type of nystagmus is most accurate for determining alcohol impairment, its presence may also indicate the use of other drugs.

(2) Vertical Gaze Nystagmus (VGN) is an involuntary jerking of the eyes (up and down) which occurs when the eyes gaze upward at maximum elevation. The presence of this type of nystagmus is associated with high doses of alcohol for that individual and certain other drugs. The drugs that cause Vertical Gaze Nystagmus are the same ones that cause horizontal Gaze Nystagmus.

Note: There is no drug that will cause Vertical Gaze Nystagmus that does not cause Horizontal Gaze Nystagmus. If Vertical Gaze Nystagmus is present and horizontal Gaze Nystagmus is not, it could be a medical condition.

(3) Resting Nystagmus is referred to as a jerking of the eyes as they look straight ahead. Its presence usually indicates a pathology or high doses of a Dissociative Anesthetic drug such as PCP. If detected, take precautions.  (Officer Safety)

Nystagmus Resulting from Pathological Disorders: NHTSA Manual 2006

Nystagmus can be caused by certain pathological disorders. They include brain tumors and other brain damage or some diseases of the inner ear. These pathological disorders occur in very few people and in even fewer drivers.