How the Horizontal Gaze Nystagmus Test Is Used in Georgia DUI Cases
During a Georgia DUI investigation, an officer may hold a pen, finger, or small light in front of a driver’s face and ask the driver to follow it with the eyes while keeping the head still. The exercise is the horizontal gaze nystagmus test, commonly called HGN.
HGN is different from roadside exercises that involve walking, balancing, or following a sequence of physical instructions. The officer is looking for involuntary jerking of the eyes as they move from side to side. Georgia courts permit HGN evidence in DUI cases, but the value of the test depends on how it was administered, the officer’s training, observations made before testing, and possible explanations for the eye movement. An experienced Georgia DUI defense lawyer can help compare the officer’s description of the HGN test with the roadside video, training standards, and other evidence surrounding the arrest.
What an Officer Looks for During an HGN Test
Horizontal gaze nystagmus refers to involuntary jerking of the eyes while a person looks from side to side. Alcohol can produce or intensify this type of nystagmus, which is why HGN became part of the standardized field sobriety testing procedures used by law enforcement.
The standardized HGN test looks for three observations in each eye. The officer checks whether the eye moves smoothly while following the stimulus, whether distinct nystagmus appears when the eye is held at maximum deviation, and whether nystagmus begins before the eye reaches approximately 45 degrees. Those observations can produce up to six clues. NHTSA’s standardized field sobriety training materials instruct officers to follow a specific sequence when conducting the examination.
Georgia appellate courts have recognized HGN as an accepted procedure that can provide evidence associated with alcohol impairment. In Duncan v. State, the Court of Appeals described the test as an accepted method while emphasizing that the officer must substantially perform the procedures in an acceptable manner.
The six clues do not amount to six separate findings that a person was drunk. They are observations made during one eye examination and interpreted within the officer’s training.
Administration Begins Before the Stimulus Moves
The test does not properly begin with an officer immediately sweeping a pen across the driver’s field of vision. NHTSA training calls for preliminary observations of the eyes.
Officers are trained to check pupil size, whether the eyes track together, and whether resting nystagmus is already present while the person is looking straight ahead. Unequal pupils or unequal tracking can indicate a medical condition, neurological problem, injury, or another circumstance that deserves attention before testing continues. Resting nystagmus can also have causes unrelated to ordinary alcohol impairment.
The environment can affect administration as well. The officer needs an appropriate stimulus position and pace and must hold the stimulus for the prescribed periods during portions of the examination. Flashing lights, difficulty seeing the stimulus, excessive speed, or failure to complete portions of the test can complicate interpretation.
Those details are often visible on body-camera or dash-camera footage. Video can show where the driver was standing, where the officer placed the stimulus, how quickly it moved, and whether preliminary eye checks occurred before the officer began scoring clues.
Officer Training Can Affect the Foundation for HGN Evidence
HGN involves observations that most drivers cannot independently verify while the test is happening. The officer’s training and experience therefore receive considerable attention when the State seeks to use the results.
Georgia courts consider whether the officer received sufficient instruction, had experience administering HGN, followed standardized techniques, and properly scored or interpreted what was observed. In Hann v. State, the Court of Appeals identified those factors while reviewing a challenge to HGN evidence. The officer had observed six clues, and the court concluded that alleged shortcomings in administration did not require exclusion because the test had been substantially performed according to the applicable guidelines.
Parker v. State reached a similar result after an officer acknowledged performing the smooth-pursuit portion of the test “a little quick.” The officer had significant HGN experience, properly completed the other components, and observed six clues. The Court of Appeals allowed the evidence despite the timing issue.
Training does not make every roadside HGN test equally reliable. It provides part of the foundation for understanding what the officer did and whether deviations from that training affected the observation.
Georgia Courts Distinguish Imperfect Administration From a Failed Test
A deviation from standardized procedures does not automatically keep HGN evidence out of court.
Georgia decisions frequently distinguish between problems serious enough to undermine the test and lesser deviations that affect how much weight the factfinder gives the evidence. Duncan provides a particularly useful example. The officer performed fewer passes than he had been trained to perform, patrol-car strobe lights may have been operating, and the driver displayed resting nystagmus before the formal test began. The Court of Appeals nevertheless concluded that the trial judge could find that the officer substantially performed the procedure.
Georgia courts have reached the opposite conclusion where a necessary part of the procedure was omitted. The Duncan court contrasted its ruling with Sultan v. State, where the officer failed to perform a portion of the test intended to determine whether the person was an appropriate subject for HGN testing.
A defense review can look beyond whether the officer made a mistake. The more useful question is what the officer skipped or changed, why that part of the procedure exists, and how the deviation affects the claimed result.
Nystagmus Can Have Causes Other Than Alcohol
Seeing nystagmus does not uniquely identify alcohol as its cause. NHTSA’s own training materials instruct officers to look for indications of medical impairment before conducting HGN. Unequal pupil size, resting nystagmus, or eyes that do not track together can indicate injury, neurological problems, or other medical conditions. Officers are also instructed to ask about eye and general health conditions before continuing.
The Georgia Court of Appeals confronted this issue directly in Duncan. The officer observed resting nystagmus before administering the formal HGN examination and acknowledged that resting nystagmus can indicate a medical condition rather than impairment. The court treated that circumstance as something the defense could use to challenge the weight of the test evidence.
Medication can create additional questions. Georgia courts have allowed HGN testimony despite evidence of medication use when the dispute concerned the weight that should be given to the officer’s observations. The inquiry can include the specific medication involved, whether it is associated with nystagmus, and whether the officer had enough information to distinguish one possible cause from another.
Medical history is especially relevant when the officer noticed an abnormality before testing and continued without exploring it.
Roadside Conditions Can Influence What the Officer Sees
HGN is usually performed beside a road rather than in a controlled clinical environment. Traffic may be passing nearby. Emergency lights can be flashing. The driver may be facing headlights or standing on uneven ground while trying to concentrate on a moving object.
Those conditions do not automatically invalidate HGN. They can affect how confidently the officer’s conclusions can be evaluated.
Duncan again provides an example. The officer acknowledged that administering the test while a patrol-car strobe light was flashing would have been contrary to his training and could affect the test. The appellate court ultimately treated the concern as going to the weight of the evidence under the circumstances of that case.
Video can provide more information than a written arrest report about the testing environment. It may reveal bright emergency lighting, traffic distractions, repeated interruptions, an unstable stimulus, or a pace that differs from the officer’s testimony about how the test was conducted.
HGN Does Not Measure a Driver’s BAC
HGN is sometimes described using language that can make the test sound closer to a breath or blood analysis than it actually is.
The officer is not chemically measuring alcohol concentration. The HGN test involves observing eye movements associated with alcohol and certain other conditions. Georgia courts allow those observations to contribute to an officer’s impairment assessment, but HGN does not produce a laboratory BAC result.
Georgia law separately defines DUI less safe under O.C.G.A. § 40-6-391(a)(1) and DUI based on specified alcohol concentration under subsection (a)(5). Chemical testing can provide evidence of alcohol concentration for a per se charge. HGN provides observational evidence.
An HGN result also does not explain the driver’s actual manner of driving. A DUI less-safe case can include evidence concerning lane position, speed, braking, an accident, speech, coordination, admissions, other field sobriety exercises, and chemical testing. HGN occupies one part of that larger evidentiary picture.
HGN Evidence Can Still Be Challenged After It Is Admitted
Admission of HGN testimony does not require a judge or jury to accept the officer’s interpretation without question.
Georgia appellate decisions repeatedly distinguish admissibility from evidentiary weight. An officer may have performed the procedure closely enough for the testimony to reach the factfinder while still leaving meaningful questions about pace, lighting, medical conditions, resting nystagmus, or other deviations. Hann and Duncan both recognize that some administration errors can affect the weight assigned to the test rather than requiring automatic exclusion.
The arrest video can be particularly useful because the officer’s conclusion is often written after the test as a simple number of clues. Footage may permit a closer examination of the steps leading to that score.
A careful review by a knowledgeable Atlanta DUI defense lawyer can compare the officer’s training and testimony with the recorded administration of the HGN test, while also examining medical information and other evidence that may affect the interpretation of the eye movements.
Contact The Spizman Firm Today
An officer’s statement that a driver showed four or six HGN clues can sound conclusive when it appears in a DUI arrest report. The test still depends on proper administration, trained observation, and circumstances that permit the results to be interpreted fairly.
Contact The Spizman Firm today to speak with an experienced Georgia DUI defense lawyer and learn how we can examine the HGN administration, roadside video, officer training, and other evidence used to support your Georgia DUI arrest.
Sources:
- Georgia Code § 40-6-391 — Driving Under the Influence of Alcohol, Drugs, or Other Intoxicating Substances law.justia.com/codes/georgia/title-40/chapter-6/article-15/section-40-6-391/
- Duncan v. State, 305 Ga. App. 268 (2010). law.justia.com/cases/georgia/court-of-appeals/2010/a10a0651.html
- Hann v. State, 292 Ga. App. 719 (2008). law.justia.com/cases/georgia/court-of-appeals/2008/a08a0011-0.html
- Parker v. State, 307 Ga. App. 61 (2010). law.justia.com/cases/georgia/court-of-appeals/2010/a10a1605.html
- National Highway Traffic Safety Administration — DWI Detection and Standardized Field Sobriety Test Resources. nhtsa.gov/dwi-detection-and-standardized-field-sobriety-test-sfst-resources
- National Highway Traffic Safety Administration — 2023 Standardized Field Sobriety Testing Refresher Participant Manual. nhtsa.gov/sites/nhtsa.gov/files/2024-09/16412-2023_SFST_Refresher_Participant_Manual-tag.pdf