Inaccuracies of the Horizontal Gaze Nystagmus Test

The National Highway Traffic Safety Administration (NHTSA) studies pertaining to Horizontal Gaze Nystagmus (HGN) contain flaws suggesting they are not reliable indicators of a  level of intoxication.  NHTSA studies allege that Horizontal Nystagmus, or the horizontal jerking of the eyes, is considered to be an indicator that a person is under the influence of alcohol or drugs.

Police officers frequently give the HGN test as one test of the NHTSA three Standardized Field Sobriety Tests (SFSTs). NHSA alleges in their materials that the HGN test is 77% accurate in determining whether a person has a 0.10 BAC or more. However, experts have criticized the administration of this test by police officers who are not an ophthalmologist trained in the detection of eye movements and or eye pathologies. Furthermore, experts have opined that the HGN test when administered according to NHTSA standards will not stand up to peer review and may lead to false results.

For a test to be scientifically valid, there must be high reliability and validity both measured by a correlation coefficient ranging from 0 to 1.0 (highest end of the scale). Reliability relates to the consistency of scores based on re-testing. Validity relates to the ability of a test to predict particular benchmarks. For a test to be reliable the reliability and validity correlation coefficient must be 0.85 or higher.  According to the 1977 NHTSA study which studied the Horizontal Gaze Nystagmus test, the validity correlation coefficient for the HGN for a person with a BAC of 0.10 was 0.67, equating to an approximate 33% better prediction than chance. In 1981, the HGN was researched again in the laboratory and the error rate was found to be 32% for a person with a 0.10 BAC.  No validity correlation coefficients were mentioned in this study. Reliability correlation coefficients were given for the HGN of 0.66.  When different officers performed the test on the same subject with the same BAC, the coefficient for the HGN dropped down to 0.59. In other words, in a laboratory condition, the officers were wrong 41% of the time that a person with a  0.10 BAC experienced Horizontal Gaze Nystagmus.

NHTSA alleges that Horizontal Gaze Nystagmus (HGN), or the horizontal jerking of the eyes, is an indicator that a person is under the influence of alcohol or drugs. According to research, there are 47 types of nystagmus which can be found in individuals, including horizontal nystagmus.  There also exist numerous causes of HGN.  The court in Schultz v. State, 664 A.2d 60, 77 (Md. App. 1995) judicially recognized (identified) THIRTY EIGHT (38) medical conditions unrelated to alcohol which can cause Horizontal Nystagmus. These conditions included:

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;  lesions; continuous movement of the visual field past the eyes; and antihistamine use.

Ophthalmologists (medical eye doctors) receive training in the detection of eye movements and or eye pathologies, including nystagmus and its causes, over many years of medical school and residency. Officers frequently receive less than 40 hours of training in learning how to assess if a person is under the influence, including learning how to conduct field sobriety tests. It therefore follows that even if an officer does correctly identify Horizontal Nystagmus, it is unrealistic given the numerous causes of horizontal nystagmus that a police officer can distinguish the cause of the Nystagmus.  As a result, officers can jump to the false premise that if they do identify HGN, that it must be indicative of ethanol (alcohol) intoxication.

Another problem experts have identified with the Horizontal Gaze Nystagmus (HGN ) test is both determining the presence of alcohol and the actual alcohol concentration. The HGN, as administered by the NHTSA protocol for the SFSTs has been cited as the only reliable index of blood alcohol when examined for its ability to distinguish BACs under and over .04% within the .00-.08% range. So it is a fallacy to use this test to determine whether someone may has a .08 BAC or above.  Also troubling is the fact that nystagmus can remain for some time even after all alcohol clears from a persons blood (a BAC of 0.00).

Post by Kentucky DUI Lawyer Stephen J. Isaacs, Isaacs Law Office.

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