Colorado Horizontal Gaze Nystagmus Test
For most individuals arrested for DUI, the horizontal gaze nystagmus test is the most unfamiliar FST. In fact, most people do not know what the officers are looking for when performing this particular test. One might expect that an officer is testing a suspect’s balance while following a light. However, the officer is actually examining the movement of a suspect’s eyes.
Nystagmus is an involuntary jerking that occurs naturally in the eyes. This jerking occurs even when a person is sober. However, when a person is intoxicated, this jerking becomes more pronounced and often occurs at a lesser angle as the eyes move from side to side.
When performing an HGN test, an officer will hold up a light or pen and ask the suspect to follow the object with their eyes from side to side. The object is held at eye level, approximately 12 inches away from the eyes, and is moved slowly from side to side. The suspect is told to keep his/her head steady. In addition, the officer should examine the suspect’s pupils in order to rule out possible medical conditions or disorders that cause nystagmus. Next, the officer will observe the suspects eyes and look for three clues in each eye:
- the eye is tracking the object smoothly;
- nystagmus occurs before the eye reaches 45 degrees; and
- distinct nystagmus as the eye reaches maximum deviation.
According to the NHTSA, when a suspect exhibits four or more clues he or she is likely to have a BAC above .08%. This conclusion is reliable 77% of the time.
However, there are many factors that cause a false positive with regard to the HGN. In fact, in Schultz v. State, 664 A.2d60, 77 (Md. App. 1995) the Court of Special Appeals of Maryland recognized 38 non-alcohol related causes of HGN including:
- problems with the inner ear labyrinth
- irrigating the ears with warm or cold water under peculiar weather conditions
- influenza
- streptococcus infection
- vertigo
- measles
- syphilis
- arteriosclerosis
- muscular dystrophy
- multiple sclerosis
- Korchaff’s syndrome
- brain hemorrhage
- epilepsy
- hypertension
- motion sickness
- sunstroke
- eyestrain
- eye muscle fatigue
- glaucoma
- changes in atmospheric pressure
- consumption of excessive amounts of caffeine
- excessive exposure to nicotine
- aspirin
- circadian rhythms
- acute trauma to the head
- chronic trauma to the head
- some prescription drugs, tranquilizers, pain medications, anti-convulsants
- barbiturates
- disorders of the vestibular apparatus and brain stem
- cerebellum dysfunction
- heredity
- diet
- toxins
- exposure to solvents, PCBs, dry-cleaning fumes, carbon monoxide
- extreme chilling
- continuous movement of the visual field past the eyes
- antihistamine use
Thus, with so many other common factors that can cause a false positive, it is a wonder how this test has even been approved for use as a FST. Nevertheless, it is used by police and courts will give it significant weight. Fortunately, a qualified lawyer can help you convince a judge or jury that the test is not a reliable indicator of intoxication.
