The Horizontal Gaze Nystagmus (HGN) Test In Florida DUI Cases
Daytona Beach HGN Test DUI Defense Lawyer
Retired Homicide Detective. Former DUI Investigator. Trial Attorney.
If you have been arrested for DUI in Florida, there is a good chance the arrest report mentions something called the Horizontal Gaze Nystagmus Test, commonly referred to as the HGN Test.
In many DUI investigations, officers describe the HGN test as one of the most important indicators of impairment.
Some officers even consider it the most reliable field sobriety exercise they administer.
However, what many people do not realize is that the HGN test is not a breath test.
It does not measure blood alcohol concentration.
It does not determine guilt.
And it is far from infallible.
Understanding how the HGN test works, its limitations, and the ways it may be challenged can be critical in defending a DUI case.
At the Law Offices of Patrick J. McGeehan, P.A., we carefully analyze HGN testing procedures in every DUI case.
Before becoming a lawyer, Patrick served as a police officer, DUI investigator, traffic homicide investigator, police instructor, and homicide detective.
He administered field sobriety exercises and later learned how to challenge them in court.
Today, he uses that experience to defend individuals charged with DUI throughout Daytona Beach, Volusia County, Flagler County, and throughout Florida.
What Is Horizontal Gaze Nystagmus?
“Nystagmus” is an involuntary jerking movement of the eyes.
The Horizontal Gaze Nystagmus test is designed to observe eye movements while a person follows a stimulus from side to side.
During the test, an officer typically asks the driver to follow an object with their eyes while keeping their head still.
The officer then watches for specific eye movements that the officer believes may indicate alcohol impairment.
Why Officers Like The HGN Test
Many officers consider the HGN test important because it is viewed as less dependent on balance and coordination than other field sobriety exercises.
Unlike:
- Walking a straight line
- Standing on one leg
- Balancing on uneven pavement
The HGN test primarily focuses on eye movements.
Because of this, prosecutors frequently emphasize HGN evidence during DUI prosecutions.
How The Test Is Performed
The officer typically uses:
- A pen
- A finger
- A flashlight
- Another visual stimulus
The stimulus is moved horizontally across the driver’s field of vision.
The officer observes the eyes while looking for specific indicators.
Proper administration is critical.
Small errors in technique can affect reliability.
The Three “Clues” Officers Look For
According to standardized training, officers generally look for three indicators in each eye.
Lack Of Smooth Pursuit
The officer observes whether the eyes track the stimulus smoothly.
Distinct Nystagmus At Maximum Deviation
The officer observes the eyes while they are held at the far edge of vision.
Onset Of Nystagmus Prior To Forty-Five Degrees
The officer estimates when eye jerking begins.
Because there are two eyes, officers frequently report up to six total clues.
The HGN Test Does Not Measure Alcohol Concentration
One of the most important facts to understand is this:
The HGN test does not measure blood alcohol concentration.
The test does not produce:
- A BAC number
- A breath test result
- A blood test result
Instead, the officer makes observations and forms an opinion.
The distinction is important.
The HGN Test Is Not Foolproof
Many people are surprised to learn that numerous factors may affect HGN observations.
Examples may include:
- Fatigue
- Head injuries
- Neurological conditions
- Eye disorders
- Certain medications
- Inner ear problems
- Medical conditions
These issues frequently become important during DUI litigation.
Medical Conditions Can Affect Results
Numerous legitimate medical conditions may influence eye movements.
Examples may include:
- Vertigo
- Concussions
- Brain injuries
- Eye disorders
- Vestibular disorders
- Certain neurological conditions
An officer may not always be aware of these issues during a roadside investigation.
Prescription Medications And HGN
Some prescription medications may affect eye movements or other observations associated with field sobriety testing.
Questions frequently arise regarding:
- Anti-anxiety medications
- Sleep medications
- Pain medications
- Muscle relaxers
The presence of an HGN clue does not automatically establish alcohol impairment.
Related Page:
DUI With Prescription Drugs
Marijuana And HGN Testing
Many people mistakenly believe HGN is a reliable marijuana impairment test.
In reality, marijuana-related DUI cases often present different issues.
The relationship between marijuana use and HGN observations is frequently a subject of dispute.
Related Page:
Marijuana DUI Defense
Officer Training Matters
The HGN test is only as reliable as the officer administering it.
Questions frequently include:
- Was the officer properly trained?
- Was the officer properly certified?
- Did the officer follow standardized procedures?
- Was the officer experienced?
Training and compliance issues often become important areas of cross-examination.
Improper Administration Of The HGN Test
The test requires specific procedures.
Potential issues may include:
Improper Positioning
The stimulus may be positioned incorrectly.
Improper Speed
The stimulus may be moved too quickly or too slowly.
Environmental Distractions
Traffic, lights, and weather may interfere.
Failure To Follow Standardized Procedures
The officer may deviate from training protocols.
These issues may affect reliability.
Body Camera Video Often Tells A Different Story
Police reports frequently summarize HGN results with a single sentence.
Body camera footage often provides a more complete picture.
Questions frequently include:
- Was the test administered properly?
- Were instructions clear?
- Did environmental factors interfere?
- Was the officer’s description accurate?
Video evidence often becomes critical.
HGN Is Only One Piece Of Evidence
Many jurors are surprised to learn that HGN testing is only one component of a DUI investigation.
Other evidence may include:
- Driving behavior
- Officer observations
- Field sobriety exercises
- Breath tests
- Blood tests
- Witness testimony
No single test automatically determines guilt.
Common Defenses To HGN Evidence
Every case is different.
Potential defenses may include:
Improper Administration
The officer failed to follow standardized procedures.
Medical Conditions
A legitimate medical condition affected the results.
Prescription Medications
Medication may explain the observations.
Lack Of Training
The officer lacked proper qualifications.
Environmental Factors
Lighting, traffic, and distractions affected the test.
Officer Misinterpretation
The officer reached incorrect conclusions.
Constitutional Violations
The legality of the stop and detention may be challenged.
HGN Evidence And Motions To Suppress
In some cases, constitutional violations may lead to suppression of evidence, including HGN observations.
Potential issues may include:
- Illegal traffic stops
- Unlawful detentions
- Lack of reasonable suspicion
- Lack of probable cause
Related Page:
Motion To Suppress DUI Evidence
Frequently Asked Questions
What Does HGN Stand For?
Horizontal Gaze Nystagmus.
Is The HGN Test Scientific?
The test is based upon principles studied in law enforcement and scientific literature, but the administration and interpretation of the test remain subject to challenge.
Can Medical Conditions Affect The Test?
Yes.
Numerous medical conditions may affect eye movements.
Can I Fail The HGN Test While Sober?
Potentially.
Many factors other than alcohol may influence the results.
Can HGN Evidence Be Challenged?
Absolutely.
Training, administration, medical conditions, and constitutional issues frequently become important defense issues.
Why Clients Choose Patrick J. McGeehan
Many attorneys handle DUI cases.
Few have administered HGN testing before becoming lawyers.
Patrick’s background includes:
- Former DUI Investigator
- Police Officer
- Police Instructor
- Retired Traffic Homicide Investigator
- Retired Homicide Detective
- Trial Attorney
Most attorneys learn HGN testing from reports and courtroom testimony.
Patrick administered field sobriety exercises himself and later learned how to challenge them.
That experience provides valuable insight when evaluating HGN evidence.
A Career Dedicated To Evaluating DUI Evidence
Every DUI case raises important questions.
Was the HGN test administered correctly?
Was the officer properly trained?
Do medical conditions explain the observations?
Can the State prove impairment beyond a reasonable doubt?
Patrick has spent decades evaluating evidence and asking those questions.
As a police officer, DUI investigator, traffic homicide investigator, homicide detective, and trial attorney, he has devoted his career to uncovering facts and protecting the rights of the accused.
That same commitment guides every DUI defense today.
Contact A Daytona Beach DUI Lawyer
The HGN test is not a breath test.
It is not a blood test.
It is not proof of guilt.
The administration matters.
The observations matter.
The evidence matters.
The defense matters.
Contact the Law Offices of Patrick J. McGeehan, P.A. today to schedule a consultation and learn how an experienced Daytona Beach DUI lawyer can evaluate HGN evidence and help protect your rights and your future.
Resources:
Leaving the Scene of an Accident With a Death
Fatal Crash Investigations in Florida