What Is The HGN Test In A Florida DUI Case?
Understanding The Horizontal Gaze Nystagmus Test
Daytona Beach DUI Defense Lawyer
Retired Homicide Detective. Former DUI Investigator. Trial Attorney.
If you were arrested for DUI in Florida, there is a good chance your arrest report contains the abbreviation “HGN.”
Many people read their report and immediately ask:
“What is HGN?”
“What does HGN mean?”
“Can I fail the HGN test?”
“How accurate is the HGN test?”
The Horizontal Gaze Nystagmus Test, commonly called the HGN Test, is one of the most frequently used field sobriety exercises in Florida DUI investigations.
Many police officers consider it one of the strongest indicators of alcohol impairment.
However, the HGN test is often misunderstood.
It is not a breath test.
It is not a blood test.
It does not directly measure alcohol concentration.
And it does not automatically prove guilt.
At the Law Offices of Patrick J. McGeehan, P.A., we carefully examine 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 Does HGN Mean?
HGN stands for:
Horizontal Gaze Nystagmus
Nystagmus is an involuntary jerking movement of the eyes.
The HGN test is designed to observe how a person’s eyes move while following an object from side to side.
According to law enforcement training, certain eye movements may be associated with alcohol consumption.
Officers use these observations to help determine whether further DUI investigation is warranted.
How Is The HGN Test Performed?
The officer usually asks the driver to:
- Stand still
- Keep their head still
- Follow an object with their eyes only
The object may be:
- A pen
- A finger
- A flashlight
- Another visual stimulus
The officer then moves the object slowly across the driver’s field of vision while observing eye movements.
The entire process generally takes only a few minutes.
What Are Officers Looking For?
Officers are trained to look for specific eye movements known as “clues.”
These clues include:
Lack Of Smooth Pursuit
The eyes appear to move unevenly while following the object.
Distinct Nystagmus At Maximum Deviation
Jerking of the eyes becomes noticeable when the eyes move as far as possible to the side.
Onset Of Nystagmus Prior To 45 Degrees
The officer believes eye jerking begins before the eyes reach approximately forty-five degrees from center.
Because each eye is evaluated separately, officers often report up to six total clues.
Can You Fail The HGN Test?
Technically, the HGN test is not graded like a school examination.
However, officers frequently report that a person “displayed clues” during the test.
The more clues the officer believes are present, the more likely the officer is to conclude impairment exists.
Those observations often become important evidence in a DUI prosecution.
Does HGN Prove You Were Drunk?
No.
The HGN test does not prove intoxication.
The test does not measure:
- Blood alcohol concentration
- Breath alcohol concentration
- Degree of impairment
Instead, the officer makes observations and forms an opinion.
That opinion may later be challenged in court.
Why Officers Consider HGN Important
Many officers believe HGN is valuable because it focuses on eye movements rather than balance and coordination.
Unlike:
- Walking a straight line
- Standing on one leg
- Touching fingertips
The HGN test does not require physical balance.
For that reason, officers often describe it as one of the most reliable field sobriety exercises.
What Can Cause HGN Besides Alcohol?
This is one of the most important questions in many DUI cases.
Alcohol is not the only factor that may affect eye movements.
Potential causes may include:
- Fatigue
- Head injuries
- Concussions
- Neurological disorders
- Inner ear problems
- Certain medications
- Eye conditions
- Medical issues
The existence of HGN does not automatically establish alcohol impairment.
Medical Conditions And HGN
Many legitimate medical conditions may influence eye movements.
Examples include:
- Vertigo
- Vestibular disorders
- Brain injuries
- Eye disorders
- Neurological conditions
An officer may not know about these conditions during a roadside investigation.
As a result, medical explanations often become important in DUI litigation.
Prescription Medications And HGN
Certain medications may affect observations associated with HGN testing.
Examples may include medications prescribed for:
- Anxiety
- Sleep disorders
- Pain management
- Muscle spasms
The presence of HGN clues does not automatically establish alcohol impairment.
Related Page:
DUI With Prescription Drugs
Does Marijuana Cause HGN?
This is a common point of confusion.
Many people assume marijuana causes the same HGN observations associated with alcohol.
The issue is far more complicated.
Marijuana DUI cases often involve different scientific and evidentiary issues.
Related Page:
Marijuana DUI Defense
Is The HGN Test Scientific?
The HGN test is based upon scientific principles and has been studied extensively.
However, the administration and interpretation of the test remain subject to challenge.
The test depends upon:
- Proper training
- Proper administration
- Proper observation
Human error remains possible.
Officer Training Matters
The reliability of the HGN test often depends on the officer conducting it.
Questions frequently include:
- Was the officer trained?
- Was the officer certified?
- Was the test performed correctly?
- Were proper procedures followed?
Training deficiencies may become important during cross-examination.
Common Problems With HGN Testing
Potential issues may include:
Improper Positioning
The stimulus may be positioned incorrectly.
Improper Timing
The object may be moved too quickly or too slowly.
Environmental Conditions
Traffic, lights, weather, and distractions may interfere.
Medical Conditions
The officer may overlook medical explanations.
Officer Error
The officer may misinterpret observations.
These issues frequently become important defense arguments.
Body Camera Footage Often Changes The Analysis
Police reports often summarize HGN results in a single sentence.
Body camera footage frequently tells a more complete story.
Questions often include:
- Was the test properly administered?
- Did the officer follow training?
- Were instructions clear?
- Were distractions present?
Video evidence frequently becomes one of the most important pieces of evidence in the case.
Can HGN Evidence Be Challenged?
Absolutely.
Many DUI defenses involve challenges to HGN evidence.
Potential challenges may include:
- Improper administration
- Lack of training
- Medical conditions
- Prescription medications
- Environmental factors
- Officer credibility
- Constitutional violations
The fact that an officer claims HGN clues existed does not automatically end the discussion.
Frequently Asked Questions
What Does HGN Stand For?
Horizontal Gaze Nystagmus.
What Is Nystagmus?
An involuntary jerking movement of the eyes.
Does HGN Prove Intoxication?
No.
The HGN test does not directly measure alcohol concentration or impairment.
Can Medical Conditions Affect The HGN Test?
Yes.
Many medical conditions may influence eye movements.
Can HGN Evidence Be Challenged?
Absolutely.
Training, administration, medical conditions, and constitutional issues frequently become important areas of challenge.
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 police 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 Examining The Evidence
Every DUI case raises important questions.
Was the HGN test performed properly?
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
If your arrest report mentions HGN, do not assume the officer’s conclusions are correct.
The test has limitations.
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