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Horizontal Gaze Nystagmus – Understanding The “Most Reliable” Roadside Test

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Horizontal Gaze Nystagmus – Understanding The “Most Reliable” Roadside Test

Horizontal Gaze Nystagmus

The horizontal gaze nystagmus test is an eye test approved by the National Highway Traffic Safety Administration(hereinafter NHTSA) as a tool to detect clues of impairment in drivers.  The HGN test is one of three psychomotor tests approved as part of the standardized field sobriety testing protocol employed by law enforcement officers throughout the United States and used here in Ohio.

HGN: What Is The Science?

Horizontal gaze nystagmusNystagmus is defined as the oscillation of the eyeball that occurs when there is a disturbance of the vestibular system or the oculomotor control of the eye.  During the test, a law enforcement officer is looking for is an involuntary motion.  A person is usually unaware of the presence of a nystagmus and cannot control it. Forkiotis, C.J. Optometric Exercise: The Scientific Basis for Alcohol Gaze Nystagmus. 59 Curriculum II, No. 7 at 9 (April 1987); Good, Gregory W.  & Augsburger, Arol R. Use of Horizontal Gaze Nystagmus as a Part of Roadside Sobriety Testing. 63 Am. J. of Optometry & Physiological Optics 467, 469 (1986); Stapleton, June M. et al. Effects of Alcohol and Other Psychotropic Drugs on Eye Movements: Relevance to Traffic Safety. 47 Q.J. Stud. on Alcohol 426, 430 (1986).

The officer is looking for a type of nystagmus wherein the eye moves slowly in one direction and then returns rapidly, sometimes referred to as a jerk or jerking nystagmus. Adams, Raymond D. & Victor, Maurice. Disorders of Ocular Movement and Pupillary Function.  Principles of Neurology.  Ch.13, 117 (4th ed. 1991).

Alcohol is a central nervous system depressant affecting many of the higher as well as lower motor control systems of the body. This results in poor motor coordination, sluggish reflexes, and emotional instability. The part of the nervous system that fine-tunes and controls hand movements and body posture also controls eye movements.

When intoxicated, a person’s nervous system will display a breakdown in the smooth and accurate control of eye movements. This breakdown in the smooth control of eye movement may result in the inability to hold the eyes steady, resulting in a number of observable changes of impaired oculomotor functioning. See, Jack E. Richman & John Jakobowski, The Competency and Accuracy of Police Academy Recruits in the Use of the Horizontal Gaze Nystagmus Test for Detecting Alcohol Impairment, 47 New Eng. J. Optometry 5, 6 (Winter 1994). [Ed. Note, The citations and quotes in this DaytonDUI blog article were taken from HERE, HORIZONTAL GAZE NYSTAGMUS: THE SCIENCE & THE LAW, A Resource Guide for Judges, Prosecutors and Law Enforcement (no authorship or suggested citation given).

Nystagmus Terms at a Glance

  • Vestibular nystagmus: caused by movement or action in the vestibular system (inner ear); four kinds: rotational, post-rotational, caloric and positional alcohol
  • Rotational nystagmus: occurs when a person is spun around
  • Post-rotational nystagmus: occurs when a person stops spiruring around
  • Caloric nystagmus: occurs when liquids of varying temperatures are put in opposing ear canals
  • Positional Alcohol Nystagmus: caused when alcohol alters the specific gravity of the blood versus the vestibular fluid
  • Neurological nystagmus: consisting of optokinetic, physiological and gaze nystagmus
  • Optokinetic nystagmus: occurs when eyes fixate on objects that suddenly move or when eyes view sharply contrasting images
  • Physiological nystagmus: naturally occurring to avoid eye strain; normally too subtle to observe
  • Gaze nystagmus: occurs when a person’s eyes move from a center position; three types: horizontal, vertical and resting

“Nystagmus” is a term used to describe a “bouncing” eye motion that is displayed in two ways: (1) pendular nystagmus, where the eye oscillates equally in two directions, and (2) jerk nystagmus, where the eye moves slowly away from a fixation point and then is rapidly corrected through a “saccadic” or fast movement. Raymond D. Adams & Maurice Victor, Principles of Neurology, ch.13, “Disorders of Ocular Movement and Pupillary Function,” 117 (4th ed. 1991).  HGN is a type of jerk nystagmus with the saccadic movement toward the direction of the gaze.

An eye normally moves smoothly like a marble rolling over a glass plane, whereas an eye with jerk nystagmus moves like a marble rolling across sandpaper. Most types of nystagmus, including HGN, are involuntary motions, meaning the person exhibiting the nystagmus cannot control it. C.J. Forkiotis, Optometric Exercise: The Scientific Basis for Alcohol Gaze Nystagmus, 59 Curriculum II, No. 7 at 9 (April 1987); Gregory W. Good & Arol R. Augsburger, Use of Horizontal Gaze Nystagmus as a Part of Roadside Sobriety Testing, 63 Am. J. of Optometry & Physiological Optics 467, 469 (1986).  In fact, the subject exhibiting the nystagmus is unaware that it is happening because the bouncing of the eye does not affect the subject’s vision.

There Are Several Know Types & Causes of Horizontal Gaze Nystagmus

A major weakness in relying on the horizontal gaze nystagmus test in the criminal justice arena is that there are multiple causes of nystagmus that have been observed.  Syndromes such as influenza, vertigo, epilepsy, measles, syphilis, arteriosclerosis, muscular dystrophy, multiple sclerosis, Korsakoff’s Syndrome, brain hemorrhage, streptococcus infections, and other psychogenic disorders all have been shown to produce nystagmus. Additionally, conditions such as hypertension, motion sickness, sunstroke, eyestrain, eye muscle fatigue, glaucoma, and changes in atmospheric pressure may result in gaze nystagmus. Pangman. Horizontal Gaze Nystagmus: Voodoo Science. 2 DWI J. 1, 3-4 (1987).

Caffeine, nicotine and aspirin (alone or in combination with alcohol) can also lead to a nystagmus which mimics a nystagmus attributable to alcohol consumption. Id. at 3-4.  Scientific literature also points to a person’s circadian rhythms or biorhythms as having an affect on nystagmus readings as the body reacts differently to alcohol at different times in the day and even fatigue nystagmus can be found in an individual, and the list, according to critics, goes on.   Id. at 3-4; Booker, J.L.  End-position nystagmus as an indicator of ethanol intoxication. Sci Justice.  41(2):113-116. (April – June, 2001).

47 Types of Nystagmus

  1. Acquired
  2. Anticipatory(Induced)
  3. Arthrokinetic(Induced,Somatosensory)
  4. Associated(Induced,Stransky’s
  5. AudioKinetic(Induced)
  6. Bartel’s(Induced)
  7. Brun’s
  8. Centripetal
  9. Cervical(NeckTorsion,Vestibular-0basilarArteryInsufficiency
  10. Crcular/Elliptic/Oblique (Alternataing Windmill, Circumduction, Diagonal, Elliptic, Gyratory, Oblique, Radiary)
  11. Congenital (Fixation, Hereditary)
  12. Convergence
  13. Convergence Invocked
  14. Disaccociated, Disjunctive
  15. Downbeat
  16. Drug Induced (Barbiturate, 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 (Agotropic, Geotro-Pic, Bechterew’s, Caloric, Compensatory,Electrical/Faradic/Gal Vanic, Labyrinthine, Pneumatic/Compression, Positional/Alcohol, Pseudo Caloric)

Obtained from Dr. L. F. Dell’Osso, Nystagmus, Saccadic Intrusions/Oscillations and Oscillopsia, 3 Current Neuro-Opthamology 147 (1989).  There are also 38 verified causes for a horizontal gaze nystagmus other than alcohol impairment.

38 Causes of Horizontal Gaze Nystagmus

  1. ProblemsWithTheInnerEarLabyrinth
  2. Irrigating The Ears With Warm Or Cold Water Under Peculiar Weather Conditions
  3. Influenza
  4. StreptococcusInfection
  5. Vertigo
  6. Measles
  7. Syphilis
  8. Arteriosclerosis
  9. MuscularDystrophy
  10. Multiple Sclerosis
  11. Korchaff’s Syndrome
  12. Brain Hemorrhage
  13. Epilepsy
  14. Hypertension
  15. Motion Sickness
  16. Sunstroke
  17. Eyestrain
  18. Eye Muscle Fatigue
  19. Glaucoma
  20. Changes In Atmospheric Pressure
  21. Consumption Of Excessive Amounts Of Caffeine
  22. Excessive Exposure To Nicotine
  23. Aspirin
  24. Circadian Rhythms
  25. Acute Trauma To The Head
  26. Chronic Trauma To The Head
  27. Some Prescription Drugs, Tranquilizers, Pain Medications, Anti-Convulsants
  28. Barbiturates
  29. Disorders Of The Vestibular Apparatus And Brain Stem
  30. Cerebellum Dysfunction
  31. Heredity
  32. Diet
  33. Toxins
  34. Exposure To Solvents, PCB’s, Dry-Cleaning Fumes, Carbon Monoxide
  35. Extreme Chilling
  36. Lesions
  37. Continuous Movement Of The Visual Field Past The Eyes
  38. Antihistamine Use

See Shultz v. State, 664 A.2d 60, 77 (Md. App. 1995) citing State v. Witte; State v. Clark, State v. Superior Court, and Mark A. Rouleau, Unreliability of the Horizontal Gaze Nystagmus Test, 4 Am.Jur. Proof of Facts 3d 439 (1989); Louise J. Gordy & Roscoe N. Gray, 3A Attorney’s Textbook of Medicine § § 84.63 and 84.64 (1990).

Alcohol and the Horizontal Gaze Nystagmus

Alcohol causes two types: alcohol gaze nystagmus, which includes HGN, and positional alcohol nystagmus. Although alcohol causes both, alcohol gaze nystagmus and positional alcohol nystagmus are very different and easily distinguishable. Testing for positional alcohol nystagmus is not a part of the standardized field sobriety test battery. Defendants sometimes claim or attempt to confuse matters by arguing that the nystagmus the officer saw was actually positional alcohol nystagmus and not alcohol gaze nystagmus.

Standards For Admissibility

Ohio Revised Code 4511.19(D)(4)(b) sets forth the standards for admissibility of the results of field sobriety tests in OVI (drunk driving) prosecutions.  See State v. Bozcar, 113 Ohio St. 3d 148, 2007-Ohio-1251, 863 N.E.2d 115 (2007).  In order for the tests to be admissible, the State must demonstrate:

  1. By clear and convincing evidence.
  2. The Officer administered the tests in substantial compliance.
  3. The testing standards for any reliable, credible, and generally accepted
  4. Including, but not limited to, the standards set by NHTSA.

The only guidance provided for determining the meaning of “substantial compliance” has come from State v. Burnside, 100 Ohio St. 3d 152, 2003-Ohio-5372 (2003), wherein the court indicated that errors that are clearly “de minimus” or “minor procedural deviations” are not substantial.  Thus, the State must set forth the testing standards, offer some testimony that the testing standards have been accepted and that the officer has substantially complied.  If the State fails to introduce testimonial or documentary evidence of the standards (most likely via the NHTSA training manual), then they have not met this burden. See Village of Gates Mills v. Mace, 2005-Ohio-2191 (Ohio Ct. App. 8th Dist., Cuyahoga County), wherein the State did not meet this burden despite the Court having its own copy of the manual.

In my practice we have seen a trend to manipulating the “substantial compliance” standard into a de facto prejudice standard.  The burden is being subtly shifted to the defendant to demonstrate that he or she was somehow prejudiced by the officer’s failure to comply with the NHTSA standards.  For example; if the officer does not articulate that he advised the suspect not to raise his or her arms, the Court says that he substantially complied by merely mentioning that he was trained in NHTSA protocols.  If, however, the defense points out that the officer did not give the proper instruction and still scored the test in a way negative to the defendant, the court may consider excluding some portion or all of the test.  Case law can be helpful on this point.

In State v. Clay, 34 Ohio St. 2d 250, 298 N.E.2d 137 (1973) the court ruled, “[h]owever, if by cross examination or otherwise, the defense places such compliance at issue, it then is incumbent upon the State, in order to maintain its burden of proof, to offer the methods and regulations into evidence and prove compliance.”  Some courts may try to take Judicial Notice of the manual (See Evid. R 201) when no manual was introduced.  In State v. Wells 2005-Ohio-5008 (Ohio Ct. App. 2d Dist., Montgomery County) held that the court cannot assume judicial notice when the record does not demonstrate a request for judicial notice or a reference to the manual by the trial court.

The 9th District Court of Appeals issued a great decision on the issue of substantial compliance.  Specifically, the issue involved giving the HGN test while the Defendant sat in the car.  The Court found that this was not substantial compliance. (State v. Haneberg 5/29/2007, 2007-Ohio-2561, 9th District Court of Appeals).

Validity Is Dependent On Standardization

The validity of Standardized Field Sobriety Tests results is dependent upon law enforcement practitioners following the established, standardized procedures for test administration and scoring. NHTSA’s SFST Student Manual states that the procedures demonstrated in the training program describe how SFSTs should be administered under ideal conditions, but that ideal conditions do not always exist in the field. Variations from ideal conditions, and deviations from the standardized procedures, might affect the evidentiary weight that should be given to test results.

According to their own manual, the HGN, Horizontal Gaze Nystagmus test is the most reliable of the three standardized field sobriety tests.  In addition, the police are trained that the HGN achieves 77% accurate at detecting subjects at or above a .10% blood alcohol concentration.  But that is not the whole story.

Officers are not told that everyone (EVERYONE) has nystagmus. The presence of alcohol merely enhances or magnifies this natural effect. In addition, they are instructed that there are 40 different kinds of nystagmus. Yes, everyone – but that is somehow not important to their training. The fact that everyone has it and there are numerous non-impairing causes of nystagmus is deemed irrelevant in the decision to arrest someone.  Worse yet, the police officers are given no (NO!) guidance in how to distinguish between the different kinds of nystagmus.  And they get no training about what questions to ask that would help them distinguish between an impairment or a natural event.  They simply don’t care! If they see it, they will use it against you. Furthermore, courts accept this in probable cause determinations.

Drugged Driving And The Horizontal Gaze Nystagmus

Drugged Driving defense attorneys are going to have to learn about the ARIDE program.  The National Highway Traffic Safety Administration’s ARIDE course is described as a bridge between the Standardized Field Sobriety Test (SFST) and Drug Recognition Expert (DRE) courses.  ARIDE, which stands for Advanced Roadside Impaired Driving Enforcement, is a 16-hour course that claims to teach officers how to look for signs of drug impairment (drugged driving) during traffic stops.  The SFST program trains officers to identify and assess drivers suspected of being under the influence of alcohol, while the DEC/DRE program provides more advanced training to evaluate suspected drug impairment. The SFST assessment is typically employed at roadside, while an officer trained as a Drug Recognition Expert (DRE) through the DEC program conducts a 12-step evaluation in a more controlled environment such as a jail or a detention facility.

The drugged driving course begins with a review of the three SFSTs followed by a practice session and then a proficiency exam. The student has two opportunities to properly demonstrate the three tests per NHTSA standards. The student is graded by a qualified NHTSA instructor and a failure to show proficiency within two attempts (if necessary) prohibits the student from continuing on in the ARIDE course.

Once proficiency is shown, the student is introduced to the general concept of “Drugs in the Human Body” and learns about typical ingestion, effects of drugs, observable signs and symptoms of impairment, and then begins the process of learning the seven major drug categories. During this overview the student is briefly introduced to some medical conditions (see session IV, page 8-9). One (1) page of materials out of 98 pages, and about 10 minutes of class time out of 16 hours, is dedicated to the discussion of medical conditions that mimic drug impairment.

DRE, HGN and Marijuana

Drugged driving is all in the eyes according the ARIDE.  The HGN (horizontal gaze nystagmus) test confirms the possibility of the presence or absence of certain categories “on board,” as will the subjects pupil size. Lack Of Convergence (LOC) of the eyes reaches a similar conclusion. LOC is simply the inability to cross one’s eyes. However, while hailed as a valid and reliable indicator, 40% of the population lack convergence (cross their eyeballs) naturally.  These eye “conditions” or “observations” alone or in combination and their presence or absence are the primary method of identifying any single or multiple drug categories.

The horizontal gaze nystagmus test is not present in marijuana impairment cases. In State v. Dixon, 2007-Ohio-5189 (Ohio Ct. App. 12th Dist. Clermont County 2007), the court addressed the issue of standardized field sobriety tests and marijuana impairment.  Relying upon the NHTSA standards, the court concluded that observations as to performance on the walk & turn test and the one-leg stand test were indicative of impairment, thus allowing those to be used against a suspected marijuana user.  The HGN test, however, is not indicative of marijuana impairment.  According to NHTSA nystagmus would not be present due to marijuana and, as such, it was plain error to admit evidence of the horizontal gaze nystagmus test against the defendant accused of marijuana impairment.

Call me if you have questions about the HGN, or any other questions about your DUI arrest. I have spent years studying, lecturing and cross-examining police officers about the Horizontal Gaze Nystagmus. I invite you to check out my credentials. Further, I hope that you will call and schedule a free consultation about your DUI case. Reach me at (937) 318-1384 or by email at CharlesRowland@CharlesRowland.com

Charles Rowland


Charles M. Rowland II has been representing the accused drunk driver for over 20 years. Contact him at (937) 318-1384 if you find yourself facing a DUI (now called OVI) charge.

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