Types and Causes of Nystagmus in Ohio HGN and OVI Cases

Learn the science behind the eye test in our field sobriety guide.

The horizontal gaze nystagmus (HGN) test is treated by police as one of the most reliable field sobriety tests, but there is a major weakness at its core: nystagmus, the involuntary bouncing of the eye that officers look for, has dozens of known types and dozens of causes that have nothing to do with alcohol. This page explains the science of nystagmus and lists the 47 recognized types of nystagmus and the 38 documented causes of horizontal gaze nystagmus other than alcohol impairment. Call (937) 318-1384 for a free consultation.

Learn about the walk and turn and one leg stand test.

What Is the HGN Test?

The horizontal gaze nystagmus test is an eye test approved by the National Highway Traffic Safety Administration (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?

Nystagmus 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 an involuntary motion. A person is usually unaware of the presence of a nystagmus and cannot control it. The officer is looking for a type of nystagmus in which the eye moves slowly in one direction and then returns rapidly, sometimes referred to as jerk nystagmus.

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, which may result in the inability to hold the eyes steady. 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. The subject exhibiting the nystagmus is usually unaware that it is happening, because the bouncing of the eye does not affect the subject’s vision.

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 spinning 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 the eyes fixate on objects that suddenly move, or when the 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.

The Many Known Types and Causes of 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.

Caffeine, nicotine, and aspirin, alone or in combination with alcohol, can also lead to a nystagmus that mimics a nystagmus attributable to alcohol consumption. Scientific literature also points to a person’s circadian rhythms or biorhythms as having an effect on nystagmus readings, as the body reacts differently to alcohol at different times of the day, and even fatigue nystagmus can be found in an individual. According to critics, the list goes on.

47 Types of Nystagmus

• Acquired
• Anticipatory (Induced)
• Arthrokinetic (Induced, Somatosensory)
• Associated (Induced, Stransky’s)
• Audiokinetic (Induced)
• Bartel’s (Induced)
• Brun’s
• Centripetal
• Cervical (Neck Torsion, Vestibular-Basilar Artery Insufficiency)
• Circular / Elliptic / Oblique (Alternating Windmill, Circumduction, Diagonal, Elliptic, Gyratory, Oblique, Radiary)
• Congenital (Fixation, Hereditary)
• Convergence
• Convergence Evoked
• Dissociated, Disjunctive
• Downbeat
• Drug Induced (Barbiturate, Bow Tie, Induced)
• Epileptic (Ictal)
• Flash Induced
• Gaze-Evoked (Deviational, Gaze-Paretic, Neurasthenic, Seducible, Setting-In)
• Horizontal
• Induced (Provoked)
• Intermittent Vertical
• Jerk
• Latent / Manifest Latent (Monocular Fixation, Uniocular)
• Lateral Medullary
• Lid
• Miner’s (Occupational)
• Muscle Paretic (Myasthenic)
• Optokinetic (Induced, Optomotor, Panoramic, Railway, Sigma)
• Optokinetic After-Induced (Post-Optokinetic, Reverse Post-Optokinetic)
• Pendular (Talantropia)
• Periodic / Aperiodic Alternating
• Physiologic (End-Point, Fatigue)
• Pursuit After Induced
• Pursuit Defect
• Pseudo Spontaneous
• Rebound
• Reflex (Baer’s)
• See-Saw
• Somatosensory
• Spontaneous
• Stepping Around
• Torsional
• Uniocular
• Upbeat
• Vertical
• Vestibular (Ageotropic, Geotropic, Bechterew’s, Caloric, Compensatory, Electrical/Faradic/Galvanic, Labyrinthine, Pneumatic/Compression, Positional/Alcohol, Pseudo-Caloric)

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

38 Causes of Horizontal Gaze Nystagmus

• 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
• Korsakoff’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, and anti-convulsants
• Barbiturates
• Disorders of the vestibular apparatus and brain stem
• Cerebellum dysfunction
• Heredity
• Diet
• Toxins
• Exposure to solvents, PCBs, dry-cleaning fumes, and carbon monoxide
• Extreme chilling
• Lesions
• Continuous movement of the visual field past the eyes
• Antihistamine use

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

Why This Matters for Your Defense

Officers are trained to treat HGN as strong evidence of alcohol impairment, but the science shows that nystagmus takes dozens of forms and can be produced by dozens of conditions unrelated to alcohol, from the inner ear and common illnesses to caffeine, nicotine, aspirin, fatigue, and medications. An attorney who understands the science can question whether what the officer saw was actually alcohol-induced nystagmus, whether the test was administered and interpreted correctly, and whether an innocent cause was overlooked. That is exactly the kind of analysis a dedicated OVI attorney brings to an HGN case.

Why Trust Charles M. Rowland II

Charles M. Rowland II has established himself as a top OVI attorney in Ohio and the Dayton area and beyond. He lives by the motto, “Work hard, play by the rules, and never quit!” Preparation, dedication and perseverance are his touchstones. He will vigorously fight for you and will genuinely care about the outcome of your case. He wants the most favorable outcome including acquittals, dismissed charges, or advantageous reduced charges.

He has been recognized by his clients and his peers as a top OVI attorney. He has been a “Super Lawyer” since 2013, a Fellow to the Ohio State Bar Foundation, the Nations Top 1%, the National Trial Lawyers Top 100 for Criminal Defense, a Dayton Bar Association Foundation Fellow, and has appeared in Time and Car & Driver Magazine for OVI defense. He completed the same NHTSA standardized field sobriety testing course that police officers attend and later became an instructor, qualified to teach officers how to administer and evaluate the field tests. He is a lecturer on OVI defense to police agencies, attorneys, judges, and students, and he taught OVI trial practice at the Greene County Peace Officer Training Academy for over fifteen years.

Charlie is a member of the Dayton Bar Association, the Dayton Bar Foundation (2022 Foundation Fellow), the Greene County Bar Association (past President), the Clark County Bar Association, the Ohio State Bar Association, the Ohio State Bar Foundation (2005 Foundation Fellow), the American Bar Association, and the American Bar Foundation.

Frequently Asked Questions Types & Causes of Nystagmus in Ohio HGN

Free Consultation

If your OVI case involves the HGN eye test, call Charles M. Rowland II at (937) 318-1384 for a free consultation.