Daytona Beach DUI Defense Lawyer
Understanding The Horizontal Gaze Nystagmus Test In Florida DUI Cases
One of the most common questions people ask after a DUI arrest is:
“How accurate is the HGN test?”
The answer is more complicated than many people realize.
Police officers frequently describe the Horizontal Gaze Nystagmus Test, commonly known as the HGN Test, as one of the most reliable field sobriety exercises used during DUI investigations.
Prosecutors often emphasize HGN evidence at trial.
Officers frequently cite HGN observations as a major factor supporting probable cause for arrest.
However, the HGN test is not perfect.
It is not a breath test.
It is not a blood test.
It does not directly measure blood alcohol concentration.
And it can be affected by numerous factors unrelated to alcohol consumption.
Understanding the strengths and weaknesses of the HGN test is important for anyone facing a Florida DUI charge.
At the Law Offices of Patrick J. McGeehan, P.A., we carefully examine HGN evidence 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 The HGN Test?
The Horizontal Gaze Nystagmus Test is a field sobriety exercise used by law enforcement officers during DUI investigations.
The test involves observing eye movements while a person follows a stimulus from side to side.
The officer typically uses:
- A pen
- A finger
- A flashlight
- Another visual object
The person is instructed to keep their head still and follow the object with their eyes only.
The officer then looks for specific eye movements believed to be associated with alcohol impairment.
Related Page:
What Is HGN?
What Do Officers Mean By “Accurate”?
When officers describe the HGN test as accurate, they are generally referring to studies that suggest certain eye movements may correlate with alcohol consumption.
However, it is important to understand what the test actually does.
The HGN test does not:
- Measure blood alcohol concentration
- Determine guilt
- Determine innocence
- Establish impairment by itself
Instead, it provides observational information that officers use as part of a larger DUI investigation.
The HGN Test Is Not A Breathalyzer
Many people mistakenly believe the HGN test works like a portable breath test.
It does not.
The HGN test does not provide:
- A numerical result
- A BAC reading
- A chemical measurement
The officer simply observes eye movements and forms an opinion.
That distinction is critically important.
Why Officers Consider HGN Reliable
Many officers believe HGN is useful because it focuses on eye movements rather than balance and coordination.
Unlike other field sobriety exercises, the HGN test is not heavily influenced by:
- Weight
- Athletic ability
- Age
- Physical strength
As a result, officers often view it as one of the stronger field sobriety exercises.
Accuracy Depends Upon Proper Administration
One of the biggest misconceptions about HGN is that it works automatically.
It does not.
The reliability of the test depends heavily upon whether the officer followed proper procedures.
Questions frequently include:
- Was the test administered correctly?
- Was the stimulus positioned correctly?
- Was the stimulus moved at the proper speed?
- Was the officer properly trained?
If procedures are not followed, reliability may be compromised.
Officer Error Can Affect Results
The HGN test requires careful observation.
Potential errors may include:
Moving The Stimulus Too Quickly
Moving The Stimulus Too Slowly
Incorrect Positioning
Failure To Follow Standardized Procedures
Misinterpreting Eye Movements
Environmental Distractions
Because the test involves human observation, mistakes can occur.
Medical Conditions Can Affect HGN Results
One of the most important limitations of the HGN test involves medical conditions.
Numerous legitimate conditions may affect eye movements.
Examples include:
- Vertigo
- Concussions
- Head injuries
- Neurological disorders
- Eye disorders
- Vestibular disorders
An officer may not know about these conditions during a roadside investigation.
As a result, innocent medical explanations are sometimes overlooked.
Fatigue Can Affect Eye Movements
Many DUI arrests occur late at night.
Drivers may be:
- Exhausted
- Sleep deprived
- Physically fatigued
Fatigue itself may affect appearance and eye function.
This often becomes an important issue during cross-examination.
Prescription Medications Can Affect HGN
Certain medications may affect eye movements.
Examples may include:
- Anti-anxiety medications
- Sleep medications
- Pain medications
- Muscle relaxers
The presence of HGN clues does not automatically mean alcohol caused those observations.
Related Page:
DUI With Prescription Drugs
Can Marijuana Affect HGN?
The relationship between marijuana and HGN remains a subject of debate.
Marijuana DUI cases often involve different scientific considerations than alcohol-related cases.
Questions frequently arise regarding:
- THC levels
- Drug recognition evaluations
- Alternative causes of impairment
Related Page:
Marijuana DUI Defense
The HGN Test Is Only One Part Of A DUI Investigation
One of the most important things jurors learn during DUI trials is that HGN is only one piece of evidence.
Other evidence may include:
- Driving behavior
- Officer observations
- Field sobriety exercises
- Breath tests
- Blood tests
- Witness testimony
No single piece of evidence automatically determines the outcome of a DUI case.
Body Camera Video Often Reveals Problems
Many DUI reports contain a brief statement such as:
“The defendant displayed six out of six clues on the HGN test.”
However, body camera footage frequently reveals important details.
Questions often include:
- Was the test performed correctly?
- Did distractions exist?
- Were instructions clear?
- Did the officer follow training?
Video evidence frequently becomes critical.
Why DUI Lawyers Challenge HGN Evidence
HGN evidence is challenged for many reasons.
Examples include:
Improper Administration
Officer Training Issues
Medical Conditions
Prescription Medication Effects
Environmental Factors
Poor Documentation
Officer Credibility Issues
The fact that an officer reports HGN clues does not automatically mean the observations were accurate.
HGN Evidence And Probable Cause
In many DUI cases, officers rely heavily on HGN observations when deciding whether to make an arrest.
Questions often arise regarding:
- The officer’s conclusions
- The totality of the circumstances
- Whether probable cause actually existed
These issues frequently become important during suppression hearings.
Related Page:
Motion To Suppress DUI Evidence
Frequently Asked Questions
Is The HGN Test 100 Percent Accurate?
No.
No field sobriety exercise is 100 percent accurate.
Does Failing The HGN Test Mean I Was Drunk?
No.
The HGN test does not directly measure alcohol concentration.
Can Medical Conditions Affect The HGN Test?
Yes.
Many legitimate medical conditions may affect eye movements.
Can Prescription Medications Affect HGN?
Yes.
Certain medications may influence observations associated with HGN testing.
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 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 Challenging DUI Evidence
Every DUI case raises important questions.
Was the HGN test administered correctly?
Was the officer properly trained?
Could 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 Defense Lawyer
The HGN test is not perfect.
It is not proof of guilt.
It is one piece of evidence that must be carefully examined.
The administration matters.
The science matters.
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