The DWI eye test is called the horizontal gaze nystagmus test. It is a field sobriety test used in DWI investigation. Nystagmus is the involuntary movement or jerking of the eyes that occurs when the eyes gaze from side to side. Nystagmus is a natural phenomenon. A number of factors may exaggerate nystagmus, including alcohol, caffeine, and stress.

The DWI eye test is one of three that comprise the standardized array of field sobriety tests. The other two are the walk-and-turn and the one-leg-stand. They are very important because how you do no them determines if you get arrested or not.

How does the DWI Eye Test Work?

To conduct the test, an officer moves a pencil or similarly-shaped object in a side-to-side motion in front of your face. It should be slightly above eye level and 12″-15″ away from your face. Alcohol consumption depresses the central nervous system and can inhibit the eyes ability to smoothly track the object. Officers are looking for a jerking movement of the eyes correlating to blood alcohol concentration.

The National Highway Traffic Safety Administration (NHTSA) claims on its website that Horizontal gaze nystagmus testing is “the most effective roadside test for impaired drivers.” However, research has shown that many people display a nystagmus that cannot be differentiated from alcohol gaze nystagmus when they turn their eyes more than 40 degrees to either side.

There are Many Causes for Nystagmus. Cops Are Not Trained to Know the Difference

There are many causes of nystagmus totally unrelated to alcohol. The truth is that cops can’t distinguish alcohol-induced nystagmus from the others. A federal case, United States v Horn, lists the seemingly endless possible causes of nystagmus:

Problems with the inner ear labyrinth; irrigating the ears with warm or cold water; influenza; streptococcus infection; vertigo; measles; syphilis; arteriosclerosis; Korchaff’s syndrome; brain hemorrhage; epilepsy; hypertension; motion sickness; sunstroke; eye strain; eye muscle fatigue; glaucoma; changes in atmospheric pressure; consumption of excessive amounts of caffeine; excessive exposure to nicotine; aspirin; circadian rhythms; acute head trauma; chronic head trauma; some prescription drugs; tranquilizers; pain medication; anti-convulsant medicine; barbiturates; disorders of the vestibular apparatus and brain stem; cerebellum dysfunction; heredity; diet; toxins; exposure to solvents; extreme chilling; eye muscle imbalance; lesions; continuous movement of the visual field past the eyes; antihistamine use

That is quite a list. In spite of all of this, the eye test can be very compelling evidence to a jury, particularly if the investigating officer is cross-examined ineffectively.

Have you been arrested for DWI? Call my office: 817-689-7002. Come in for a free and confidential case evaluation. We are downtown at 108 Main Street, Fort Worth, TX,76102