Vestibular System Disturbance

While the National Highway Traffic and Safety Administration (NHTSA) guidelines support horizontal gaze nystagmus as a determining factor for intoxication or drug influence, there is a great deal of concern by public interest groups who refute this test as inaccurate and unfair in judging so serious a crime as DUI.

Non-Alcohol Causes Of Nystagmus

The NHTSA stands firm on its findings that alcohol-impaired persons show clear signs of altered nystagmus. Sound research by public interest groups cite a range of physical disabilities that can cause the same impaired nystagmus reactions:

• Car or motion sickness or other illnesses such as a cold or flu that affect the sinuses
• Eye disease or abnormalities
• Contact lenses
• Ear infections
• Sunstroke
• Eye muscle fatigue, such as created by long hours of driving
• Vertigo
• Medications or ingredients that are acceptable to use while driving, including caffeine, nicotine, aspirin, and cold remedies
• Congenital defects
• As a side-effect of neurologic disease.

The Law Enforcement Arsenal Of Sobriety Tests

The NHTSA position is that a law enforcement officer typically uses three tests to determine if a driver is under the influence of drugs or alcohol. These ‘standardized field sobriety tests’ are:

• The one-leg stand
• Walk and turn, and 
• Horizontal gaze nystagmus test.

Police officers are trained by the NHTSA in conducting these test to increase their accuracy. In addition, an officer is likely to administer a breathalyzer, blood, or urine test soon after these field sobriety tests to more accurately determine BAC.