GLOSSARY OF TERMS

alcohol gaze nystagmus (AGN) - Gaze nystagmus caused by the effects of alcohol upon the nervous system.

caloric nystagmus - A vestibular system nystagmus caused by differences in temperature between the ears, e.g., one ear is irrigated with warm water and the other irrigated with cold water.

epileptic nystagmus - Nystagmus evident during an epileptic seizure.

field sobriety test (FST) - Any number of tests used by law enforcement officers, usually on the roadside, to determine whether a driver is impaired. Most FSTs test balance, coordination and the ability of the driver to divide his or her attention among several tasks as once. Other tests, such as the horizontal gaze nystagmus test, are used to measure a subject's impairment level.

fixation - ability of the eye to focus on one point.

gaze nystagmus - Nystagmus that occurs when the eyes gaze or fixate upon an object or image. Usually caused by a disruption of the nervous system.

horizontal gaze nystagmus (HGN) - Gaze nystagmus that occurs when the eyes gaze or move to the side along a horizontal plane.

jerk nystagmus - Nystagmus where the eye drifts slowly away from a point of focus and then quickly corrects itself with a saccadic movement back to the point of focus.

National Highway Traffic Safety Administration (NHTSA) - The agency within the United States Department of Transportation that administers traffic safety programs. NHTSA's duties include funding studies on field sobriety tests and training law enforcement officers in the administration of the standardized field sobriety test battery.

natural nystagmus - Nystagmus that occurs without any apparent physiological, vestibular, or neurological disturbance. Natural nystagmus occurs in approximately 2%-4% of the population.

neurological nystagmus - Nystagmus caused by some disturbance in the nervous system.

nystagmus - An involuntary bouncing or jerking of the eye caused by any number of vestibular, neurological or physiological disturbances.

oculomotor - Movement of the eyeball.

one-leg-stand (OLS) test - One of the three tests that make up the standardized field sobriety test battery. This test requires a subject to stand on one leg, look at his or her foot and count out loud to thirty. The subject is assessed on the ability to understand and follow instructions as well as the ability to maintain balance for thirty seconds. [post-publication note (August 1999), sentence should read: "...count out loud until told to stop."]

optokinetic nystagmus - A nystagmus evident when an object that the eye fixates upon 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 is also caused by watching alternating moving images, such as black and white spokes on a spinning wheel.

oscillate - to move back and forth at a constant rate between two points

pathological disorder - Disruptions of the normal functions of organs of the body due to disease, illness, or damage.

pendular nystagmus - Nystagmus where the eye oscillates or swings equally in two directions.

physiological nystagmus - A nystagmus that occurs so that light entering the eye will continually fall on non-fatigued cells on the retina. Physiological nystagmus is so slight that it cannot be detected without the aid of instruments and it occurs in everyone.

positional alcohol nystagmus (PAN) - Positional nystagmus when the foreign fluid is alcohol.
PAN I - The alcohol concentration is higher in the blood than in the vestibular system.
PAN II - The alcohol concentration is lower in the blood than in the vestibular system.

positional nystagmus - Nystagmus that occurs when a foreign fluid is in unequal concentrations between the blood and the fluid in the semi-circular canals of the vestibular system.

post-rotational nystagmus - Nystagmus caused by disturbances in the vestibular system fluid when a person spins around. Post-rotational nystagmus lasts for only a few seconds after a person stops spinning.

resting nystagmus - Nystagmus that occurs as the eye are looking straight ahead.

rotational nystagmus - Nystagmus caused by disturbances in the vestibular system fluid when a person spins around. Rotational nystagmus occurs while the person is spinning.

saccadic - Movement of the eye from one fixation point to another.

smooth pursuit - The eye's course as it tracks a moving image.

Southern California Research Institute (SCRI) - A research organization that conducted the first two research studies that eventually produced the standardized field sobriety test battery. SCRI has conducted subsequent field sobriety test validation studies as well as drug recognition evaluation studies.

standardized field sobriety test (SFST) battery - A group of tests selected as the best field sobriety tests to increase the ability of law enforcement officers to detect driver impairment. The results of this battery, usually administered along the roadside, contribute extensively to a law enforcement officer's decision to arrest a person for impaired driving.

walk-and-turn (WAT) test - One of the three tests that make up the standardized field sobriety battery. This test requires a person to take nine heel to toe steps down a straight line, turn and take nine heel to toe steps back up the line. The subject is assessed on the ability to understand and follow instructions as well as the ability to maintain balance during the instruction stage and walking stage.

vertical nystagmus - nystagmus that occurs when the eyes gaze or move upward along a vertical plane.

vestibular system - The system of fluid-filled canals located in the inner ear that assists in balance, coordination and orientation.

vestibular system nystagmus - Nystagmus caused by a disturbance in the vestibular system.