What does Horizontal Gaze Nystagmus (HGN) mean?
Let’s break down the terms:
- “Horizontal” – the officer moves his finger or pen to the right and left (versus up and down).
- “Gaze” – you look (gaze) straight ahead without moving your head.
- “Nystagmus” – an involuntary jerking of the eye.
How should the HGN test be given?
The biggest problem is that officers almost universally use the same timing for each of the three subtests. The proper procedure, as stated in the NHTSA Student Manual, is:
Pre-test #1: Screen for equal tracking, equal pupil size, and resting nystagmus.
- Unequal tracking or unequal pupils do not indicate intoxication, they typically signal a serious medical problem. The same is true if the officer sees nystagmus with no movement of the stimulus (finger or pen).
- For the next three tests, the stimulus should be held 12 – 15 inches away from the eyes and slightly above eye level. If the pen is held too high, the movement of the eye will switch off between different eye muscles – this will look like a lack of smooth pursuit.
Test #1: Lack of smooth pursuit
- A lack of smooth pursuit is sometimes compared to windshield wipers skipping across a dry windshield – the eye will hesitate and then skip to catch up with the stimulus.
- To test for smooth pursuit, the officer should take 2 seconds to move his finger from the center line of the face to the right, 2 seconds from the right to center, 2 seconds from center to left, and 2 seconds back. The test should then be repeated to ensure accuracy. The repeat is rarely done.
- If the pen or finger is moved too fast, nystagmus will occur even in totally sober people.
Test #2: Distinct and sustained nystagmus at maximum deviation
- To see if distinct and sustained nystagmus is present, the officer should move his pen so that there is no white of the eye present.
- The stimulus must be held stationary in this position for at least 4 seconds. The NHTSA Manual states that even the unimpaired will exhibit nystagmus for a “few seconds.” The procedure should be repeated for accuracy.
Test #3: Onset of nystagmus prior than 45 degrees
- This test requires an officer to estimate 45 degrees by the side of the road in the dark.
- To test for onset prior to 45 degrees, the officer should take 4 seconds to move his finger from the center line of the face to the right, and then 4 seconds from center to the left. Once jerking is seen, the officer should stop and confirm that the jerking continues.
- The test should then be repeated to ensure accuracy. The repeat is rarely done.
Can the HGN Test accurately diagnose alcohol intoxication?
No. There are three main problems with the HGN test. First, very few officers perform the test correctly. Second, the HGN test is not specific for alcohol intoxication. Third, there are 47 types of nystagmus – officers are not trained to distinguish between the different types of nystagmus.
(1) Incorrect performance
One peer reviewed study of officer technique showed that a whopping 98% of officers do not perform the HGN test correctly. 98%! We see this all the time in the officer’s videos. There are 3 subtests to the HGN and each subtest has a different timing. The vast majority of officers use the same 2 second timing on all of the tests. Even fewer ever repeat the tests as instructed for accuracy.
Many judges will suppress the results of the HGN test when we show that the officers used the wrong technique. This is important because almost every DWI checklist will say that “the defendant exhibited all 6 out of 6 clues for HGN.” In other words, clients consistently “fail” the HGN more than any other test. In reality, it’s the officer that is failing.
Mike and Jeff are trained, tested, and certified field sobriety test operators. They carry the National Highway Traffic Safety Administration (NHTSA) field sobriety test manual in their trail briefcases to cross examine officers.
(2) Other things cause nystagmus
An accurate test must be specific for the one thing it is testing for. The problem with the Horizontal Gaze Nystagmus test is that it is not specific for alcohol intoxication. Peer reviewed scientific studies found that nystagmus can be caused by …
- Disease: Parkinson’s disease, Alzheimer’s disease, hypoglycemia, diabetic vasculopathy, arteriosclerosis, progressive supranuclear palsy, cerebellar disorders, hepatic encephalopathy, cerebral lesions, inner ear problems, influenza, streptococcus infections, vertigo, measles, syphilis, muscular dystrophy, multiple sclerosis, Korsakoff’s syndrome, brain hemorrhage, epilepsy, psychogenic disorders, hypertension, motion sickness, unilateral lesions (vascular, neoplastic), diffuse brain damage (epileptics, degenerative diseases, inflammatory, traumatic)
- Eye problems such as optic neuritis, sunstroke, eye muscle fatigue, eye socket tumor, glaucoma, Brown’s syndrome, circadian rhythms, refractive errors.
- Physical surroundings like looking into the sun, changes in atmospheric conditions, insufficient lighting, night, seeing occurrences with high interest value in the background (tow truck hooking up car), traffic moving in opposite direction as stimulus.
- Drugs like caffeine, nicotine, aspirin, antihistamines; Benzodiazepines for anxiety, muscle spasms insomnia, agitation, seizures: Xanax, Valium, Ativan, Klonopin, Restoril, Serax, Rohypnol, Halcion, Librium, Dalmane, Mogadon, Ambien; Phenytoin for treatment of seizures: Dilantin, Phenytek; Carbamazepine for mood swings, bipolar disorder, seizures: Tegretol, Biston, Calepsin, Carbatrol, Epitol, Equetro, Finlepsin, Sirtal, Stazepine, Telesmin, Timonil; Barbituates for agitation, pain, anxiety: Phenobaribitol, Seconal, Amitryl; Lithium for mood, bipolar disorder: Carbolith, Cibalith-S, Duralith, Eskalith, Lithane, Lithizine, Lithobid, Lithonate, Lithotabs; Narcotics for pain: Morphine, Codeine, Dilaulid, Percodan.
- Exposure to solvents, dry cleaning fumes, carbon monoxide.
(3) 47 types of nystagmus that are not horizontal gaze
(1) Acquired; (2) Anticipatory (induced); (3) Arthrokinetic (induced, somatosensory); (4) Associated (induced, Stransky’s); (5) Audio kinetic (induced); (6) Bartel’s (induced); (7) Brun’s; (8) Centripetal; (9) Cervical (neck torsion, vestibular-basilar artery insufficiency); (10) Circular/Elliptic/Oblique (alternating windmill, circumduction, diagonal, elliptic, gyratory, oblique, radiary); (11) Congenital (fixation, hereditary); (12) Convergence; (13) Convergence-evoked; (14) Dissociated (disjunctive); (15) Downbeat; (16) Drug-induced (barbituate, bow tie, induced); (17) Epileptic (ictal); (18) Flash induced; (19) Gaze-evoked (deviational, gaze-paretic, neurasthenic, seducible, setting-in); (20) Horizontal; (21) Induced (provoked); (22) Intermittent Vertical; (23) Jerk; (24) Latent/Manifest Latent (monocular fixation, unimacular); (25) Lateral Medullary; (26) Lid; (27) Miner’s (occupational); (28) Muscle-Paretic (myasthenic); (29) Optokinetic (induced, optomotor, panoramic, railway, sigma); (30) Optokinetic After-Induced (post-optokinetic, reverse post-optokinetic); (31) Pendular (talantropia); (32) Periodic/Aperiodic Alternating; (33) Physiologic (end-point, fatigue); (34) Pursuit After-induced; (35) Pursuit Defect; (36) Pseudo spontaneous; (37) Rebound; (38) Reflex (Baer’s); (39) See-Saw; (40) Somatosensory; (41) Spontaneous; (42) Stepping Around; (43) Torsional; (44) Uniocular; (45) Upbeat; (46) Vertical; (47) Vestibular (ageotropic, geotro-pic, Bechterew’s, caloric, compensatory, electrical/faradic/gal vanic, labyrinthine, pneumatic/compression, positional/alcohol, pseudo caloric.
Do all Judges accept Horizontal Gaze Nystagmus? (HGN)
No, judges are split in federal and state courts in Virginia as to whether they let officers testify to the results of the HGN test.
Although Virginia has not formally adopted the Frye or Daubert test to establish the admissibility of scientific evidence, the standard in Virginia is somewhat close. Virginia’s Supreme Court decided:
We have declined to adopt the “Frye test” in Virginia. When scientific evidence is offered, the court must make a threshold finding of fact with respect to the reliability of the scientific method offered, unless it is of a kind so familiar and accepted as to require no foundation to establish the fundamental reliability of the system, such as fingerprint analysis; or unless it is so unreliable that the considerations requiring its exclusion have ripened into rules of law, such as “lie-detector” tests; or unless its admission is regulated by statute, such as blood-alcohol test results. Spencer
In other words, the Walk and Turn Test and the One Leg Stand measures behaviors that a lay person would commonly associate with intoxication – when you see someone staggering down the street you think that they are wasted!
On the other hand, how many of us grew up knowing that alcohol can make your eyes twitch? And even if you knew this, did you know the difference between ordinary nystagmus and “distinct and sustained?” This is why Virginia judges may require that an expert (other than the officer) use his or her specialized knowledge to establish the scientific reliability of HGN. Horizontal Gaze Nystagmus relies on greater scientific and medical principles than the other field sobriety tests.
The Supreme Court of Virginia, in Billips, recognized that “the judicial system may gravitate toward uncritical acceptance of any pronouncement that appears to be ‘scientific,’ and the more esoteric the field, the more difficult it becomes for laymen to greet it with skepticism. That tendency has given rise to frequent complaints of “junk science” in the courts.
What makes a scientific method reliable?
Even though Virginia courts have not officially accepted the Daubert test, its five factors can still be argued to reject the reliability of scientific evidence:
- whether the particular scientific theory “can be (and has been) tested”;
- whether the theory “has been subjected to peer review and publication”;
- the “known or potential rate of error”;
- the “existence and maintenance of standards controlling the technique’s operation”; and
- whether the technique has achieved “general acceptance” in the relevant scientific or expert community.
Daubert rightly considers whether scientific research has been published in a peer reviewed journal. It’s interesting to note that Virginia’s breath test machine, the Intox EC/IR II has no peer reviewed, published tests. We’re left to trust the manufacturer. Amazingly, the NHTSA field sobriety test research has never been published in a peer reviewed journal.