Horizontal Gaze Nystagmus
February 13, 2008
Nystagmus is a rhythmic, tremor-like movement of the eye. Crudely defined as a pulsation or twitching which occurs with a lateral or horizontal movement of the eye, when associated with alcohol it is not a new phenomenon. The effect of alcohol upon eye motions having been observed in animals as early as 1826. 1897 saw the first published report noting the occurrence of nystagmus in human beings following the consumption of ethanol.[i] In 1911, researchers noted that alcohol induced nystagmus underwent a change as the head was moved from the left lateral to right lateral position. Called Positional Alcohol Nystagmus or PAN, detailed studies in the late fifties by Aschan[ii] documented a downward motion during the absorption phase called (PAN I), a period with no positional nystagmus lasting approximately 90 minutes and a period of movement toward the uppermost ear that coincided with elimination of alcohol from the system (PAN II).
While positional alcohol nystagmus is of concern to those entrusted with attempting to figure out the cause of automobile and aircraft accidents,[iii] it is not viewed as a particularly reliable indicium of intoxication. For that we turn to Horizontal Gaze Nystagmus or HGN.
HGN is a form of gaze nystagmus or pulsation that is induced by lateral deviation of the eye. By lateral deviation we mean the horizontal motion that is produced when the eye is drawn to the left or right by the examiner. It is not present when the eye is looking straight. The point where this rhythmic pulsation first occurs is known as the angle of onset, the determination of which is critical when attempting to use HGN for determining intoxication.
Also discussed with HGN is the concept of smooth pursuit or the ability of the eye to track a moving object smoothly It represents an impairment of the neural mechanisms that control the movement of the eye and can be brought on by the ingestion of alcohol.
Of paramount importance in the inability of the eye to maintain a consistent lateral gaze, or HGN, is a documented correlation between a decrease in the degree to which the eye can gaze to the side, and an increase of blood alcohol content (BAC). First noted by Lehti in 1976,[iv] Tharp, et. al., developed the following equation to describe the degree to which lateral gaze was affected:
O ' 51 G 100 (BAC as % w/v)
Solving for the angle of onset [O] or the point where pulsation is first observed, the following simplification has been developed for use in the field:
BAC ' 50 G Angle of onset.
In theory, this formula is fairly easy to employ. The administering officer constructs a 90 degree angle by first drawing an imaginary line through the midline of the skull. This line represents zero degrees. A second imaginary line perpendicular to the first and drawn through the ears becomes 90 degrees. Thereafter, the officer, by smoothly moving a target such as a pen or penlight watches for the onset of pulsation. The point at which this action is first noted is the "angle of onset." This means that if the onset angle was 40 degrees, then the BAC would be expected to be approximately .10% (50 G 40). Likewise, with an onset angle of 35 degrees one would expect to find a BAC of .15% (50 G 35).
In a study conducted by Goding and Dobie,[v] 37 patients in an emergency room were tested using the above formula. Of 20 patients with a BAC in excess of .20% w/v, 17, or 85%, had an angle of onset of less than 30 degrees and all 20 showed onset at 40 degrees or less. The measured BAC of six patients was between .10% and .20% and five of the six had an angle of onset of 40 degrees or less. In one patient with a BAC of .155%, onset occurred at 45% suggesting a BAC of .05%.
In the eleven patients that remained, the results were not as good. Four patients with a BAC of less than .10% had an angle of onset of less than 40 degrees, thus falsely indicating intoxication. These false positive were found as a result of drugs such as diphenhydramine, phenytoin and meperidine.
When the authors conducted a similar examination using experienced members of the Seattle police department, BAC estimating errors were had in approximately 10% of the cases, of which 86.86% resulted in overestimation, in one instance as great as .09%.
While Goding and Dobie achieved results greater than the 78% predicted by Burns & Moskowitz in their 1981 study,[vi] it must be recognized that this was a comparatively small sample and that the angle of onset was measured using a nystagmus protractor, whereas in actual practice nystagmus is crudely estimated using crutches such as the disappearance of the white of the eye. Indeed, even NHTSA recognizes the need for accuracy in administration, noting that "nystagmus angle of onset is an excellent tool for predicting the BAC when it is measured with sufficient precision."[vii]
Moreover, not all researchers agree on the existence of a relationship between the angle of onset and BAC. Norris,[viii] for instance, rejected the existence of virtually any relationship between onset and BAC. Others, most notably Aschan, the grandfather of Nystagmus research, described a 40 degree angle of onset at a BAC of .06% and found nystagmus to persist for more than five hours after the disappearance of all alcohol from the body.[ix] Also, there exists a lively debate as to occurrence of "normal nystagmus." While NHTSA places this figure at 4.4%, Toglia states that nystagmus at 40 degrees and greater exists in 50-60% of the sober population.[x] Even the hour of administration may have a role to play. Tharp, et. al., in a 1981 NHTSA study[xi] reported that "the effects of fatigue or circadian rhythms on gaze nystagmus could be significant," observing that "the alcohol dose decreased the angle of onset by an additional five degrees after midnight." Finally, detection of HGN is complicated by the presence of end point nystagmus or pseudonystagmus. This phenomenon, which occurs normally in many individuals, disappears when the gaze is shifted centrally, or toward the nose a few degrees. Pseudonystagmus, therefore, strongly resembles HGN and has been described in the literature as difficult to determine from true nystagmus.[xii]
While several New York police agencies, most notably the New York State Police, routinely employ HGN for detecting and measuring intoxication, a close examination of the technique as employed raises grave concerns. For instance, NHTSA instructs the officer to observe the subject and take note of "the first sign of jerking." HGN, however, is far more than "jerking." An officer looking merely for "jerking" may record rotary or PAN, although both are undesired side affects. Whereas NHTSA administered placebos to those with natural nystagmus or who were taking prescription drugs known to produce such results, in practice officers do not take an adequate history prior to administration of the test. Troublesome is that given the "jerking" definition that is taught, a history should include all alcohol consumption within the last 24 hours. Given the circumstance in which the test is administered, it does not seem probable that a forthright history can be obtained. Contact lenses also create problems. Whereas NHTSA now recommends that they be removed,[xiii] officers frequently fail to ask if they are being worn and of course removal under the circumstances creates difficulties that are perhaps insurmountable.
Perhaps the greatest impediment to the use of HGN is its unquestioned lack of specificity. As recently recognized by the Supreme Court of Kansas in State v Witte, (1992) 836 P.2d 1110: "Nystagmus can be caused by problems in an individual's inner ear * * *. Physiological problems such as certain kinds of diseases may also result in gaze nystagmus. Influenza, streptococcus infections, vertigo, measles, syphilis, arteriosclerosis, muscular dystrophy, multiple sclerosis, Korsakoff's Syndrome, brain hemorrhage, epilepsy, and other psychogenic disorders all have been shown to cause nystagmus. Furthermore, conditions such as hypertension, motion sickness, sunstroke, eyestrain, eye muscle fatigue, glaucoma, and changes in atmospheric pressure may result in gaze nystagmus. The consumption of common substances such as caffeine, nicotine, or aspirin also lead to nystagmus almost identical to that caused by alcohol consumption."
While cases regulating HGN run the gamut, in New York, the test has been rejected on foundational grounds. In People v Erickson, (1989, 3rd Dept) 156 AD2d 760, 549 NYS2d 182, the Court found admission to be error, albeit harmless. A similar outcome was reached in People v Torrey, (1988, 3rd Dept) 144 AD2d 865; 534 NYS2d 807. In Torrey, the Third Department, citing the Frye standard, found the proof insufficient to warrant admission, although such admission was ultimately held to constitute harmless error.
When confronted with HGN, question the officer as to his or her training. If the officer will admit that the NHTSA publications are authoritative, explore with particularity the degree to which he or she followed its procedures. If the officer acknowledges the danger presented by contact lenses or organic conditions such as seizure disorders, see if an adequate history was taken. If it appears that HGN will be an issue at trial, explore the possibility of retaining an ophthalmologist or an optometrist to testify as to the nonspecificity of the technique. While we will leave it to others to characterize the officer's technique as "eye-balling," it is helpful to distinguish the officer's examination from the sophisticated techniques medically employed for nystagmus measurement.
[i].Joffroy A., Serveaux R., NMensuration de la toxicité vraie de l'alcool éthylique: symptômes de l'intoxication aigu et de l'intoxication chronique par l'alcool éthylique. Arch. Méd Exp 1897;9:681-707.
[ii].Aschan G., "Different Types of Alcohol Nystagmus," Acta Otolaryngol, 1958:140:69-78.
[iii].Gibbons, Harry L., Alcohol, "Aviation, and Safety Revisited: A Historical Review and a Suggestion," Aviation, Space and Environmental Medicine, July, 1988, pp 657- 660.
[iv].Lehti, H., "The Effects of Blood Alcohol on the Onset of Gaze Nystagmus," Blutalkohol, 13:411-414, 1976.
[v].Goding, G. S., Dobie, R. A., "Gaze Nystagmus and Blood Alcohol," The Laryngscope 96:July 1986, pp. 713-717.
[vi].Burns, M., and Moskowitz H., "Psychophysical Tests for DWI Arrest," National Highway Traffic Safety Administration Contract No. DOT-HS-5-01242 (1977).
[vii].|Emphasis supplied herein\
[viii].Norris, "The Correlation of Angle of Onset of Nystagmus with Blood Alcohol Level: Report of a Field Trial." 25 Journal of Forensic Science 476 (1986).
[ix].Aschen, Bergstedt, Goldberg, & Laurell, "Positional Nystagmus in Man During and After Alcohol Intoxication," 17 Q.J. of Studies on Alcohol 381, Sept., 1956.
[x].Toglia, Electronystgmography: Technical Aspects and Atlas, (1976).
[xi].Tharp, Burns and Moskowitz, "Development and Field Tests of Psychophysical Tests for DWI Arrest," DOT-HS-805-864 (1981).
[xii].Walsh, F. B., Hoyt, W. F., Clinical Neuro-Ophthalmology, 3rd ed., vol. 1, p. 283.
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