Horizontal Gaze Nystagmus (HGN) Test 
If you have been arrested for a DUI then you have probably been subjected to the DUI Eye Test, more commonly known as the Horizontal Gaze Nystagmus (HGN). This test is actually one of three (3) standardized tests recognized by the National Highway Transportation Safety Administration (NHTSA). If properly administered, many police departments swear by the results and often take the position no other testing is necessary. Nystagmus is an “involuntary jerking” of the eyes which officers claim cannot be “faked” by those individuals who have been drinking or using certain types of drugs. Of course, even NHTSA research has concluded this test is only accurate to a limited degree in the best of conditions. In this article, we show other possible, non-impaired, reasons why some people will have HGN without any relation to alcohol consumption.
In the HGN test, the officer observes the eyes of a suspect as the suspect follows a slowly moving object such as a pen or small flashlight, horizontally with his or her eyes. The examiner looks for three indicators of impairment in each eye: if the eye cannot follow a moving object smoothly, if jerking is distinct when the eye is at maximum deviation, and if the angle of onset of jerking is within 45 degrees of center. If, between the two eyes, four or more clues appear, the suspect likely has a BAC of 0.08 or greater. As you’re probably thinking right now, this test is far from being scientifically accurate. As you also guessed, there are many reasons other than alcohol that are medically known to cause this jerk. Many of these medical conditions are listed below. Do any of these apply to you?
- inner ear infection or condition
- irrigating ears with warm or cold water
- influenza
- streptococcus infection
- natural or induced vertigo
- measles
- syphilis
- arteriosclerosis
- muscular dystrophy
- multiple sclerosis
- Korchaff’s syndrome
- brain hemorrhage
- epilepsy
- hypertension
- motion sickness
- sunstroke
- eye strain
- eye muscle fatigue
- glaucoma
- atmospheric pressure changes
- excessive caffeine
- excessive nicotine
- aspirin usage
- circadian rhythm changes
- acute head trauma
- chronic head trauma
- certain prescription drugs, tranquilizers, pain medications
- barbiturates
- neural disorders of the vestibular apparatus and brain stem
- cerebellum dysfunction
- heredity
- diet
- toxins
- exposure to solvents, PCBs, dry cleaning fumes, carbon monoxide
- extreme chilling
- eye muscle imbalance
- certain lesions
- the continuous movement of the visual field past the eyes
- antihistamine use
As you can now see, there are many reasons for HGN in persons without having consumed any alcohol. There are also improper testing reasons for a false HGN finding that we will show in a subsequent posting. For now, just know that DUI suspects who “fail” HGN testing may have a number of valid and persuasive defenses at their disposal. And, HGN testing is just one of many factors that can be challenged in a DUI arrest.
Be Safe. Get Home.