What Is the HGN Test?
The Horizontal Gaze Nystagmus (HGN) test is a roadside eye test police use during DUI/OVI stops. “Nystagmus” means an involuntary jerking of the eyes. Alcohol and certain drugs can make this jerking start sooner and become more noticeable when a person looks to the side. Officers look for specific eye-movement “clues” that can suggest impairment.
How Officers Use the HGN Test
During a traffic stop, an officer may ask a driver to follow a small object, such as a pen or fingertip, with just their eyes. The officer moves the object side to side and watches the driver’s eyes. The officer looks for up to six clues, three in each eye:
1. Lack of smooth pursuit (the eye jerks instead of tracking smoothly)
2. Distinct nystagmus at maximum deviation (clear jerking at the far side)
3. Onset of nystagmus prior to 45 degrees (jerking starts before the eye reaches a 45-degree angle)
More clues generally suggest a higher likelihood that the person is impaired by alcohol. Officers often use HGN together with other field sobriety tests and observations and may use the results to decide whether to request a breath or blood test or to make an arrest.
Ohio Law: Requirements for Proper HGN Administration
In Ohio, officers are expected to administer the HGN test in substantial compliance with standardized procedures. While each case is fact-specific, proper administration in Ohio typically includes: - Positioning: The stimulus (pen or similar object) should be held slightly above eye level, about [12–15 inches] from the face. - Instructions: The officer should tell the person to keep the head still and follow the object with the eyes only. - Medical checks: A brief check for equal pupil size, equal tracking in both eyes, and resting nystagmus should occur before the test. - Speed and timing: The officer should move the stimulus at a controlled speed, pausing long enough at maximum deviation to observe for nystagmus, and using appropriate timing for each pass. - Observation of clues: The officer should make separate, systematic passes for each of the three clues in each eye, and should not rush the sequence. - Environment: The setting should minimize distractions, with the subject standing on a reasonably level surface, and the officer should note wind, weather, flashing lights, or other factors that could affect the eyes. - Documentation: The officer should record how the test was performed, the clues observed, and any conditions that might affect the results.
If the test is not performed in substantial compliance with standardized methods, a court in Ohio may limit or exclude the HGN evidence. Defense counsel often examines whether the officer followed training, timing, positioning, and proper instructions in accordance with accepted standards.
Common Criticisms of the HGN Test
Even though HGN is widely used, there are several criticisms from other states and from medical and legal commentators:
- Medical and scientific concerns:
- Alternative causes: Fatigue, certain neurological conditions, eye disorders, head injuries, and some prescription or over-the-counter medications can cause nystagmus similar to alcohol-related signs.
- Environmental factors: Wind, moving lights (such as patrol car flashers), and roadside distractions may influence eye movements or an officer’s observations.
- Administration variability: Small errors in stimulus distance, speed, angle, or timing can change what the officer sees and lead to inconsistent results.
- Drug impairment differences: Not all drugs affect HGN the same way as alcohol, so HGN alone may not reliably indicate impairment by non-alcohol substances.
- Legal and procedural concerns:
- Training and consistency: Courts in some states have questioned HGN results when officers did not follow standardized procedures closely or lacked proper training documentation.
- Overreliance: Some decisions outside Ohio have cautioned against treating HGN as a stand-alone proof of intoxication, emphasizing that it should be considered with all other evidence, not in isolation.
- Jury understanding: Because HGN involves technical, physiological concepts, there is a risk that juries may give it more weight than it deserves without careful explanation and limits on testimony.
- Record-keeping: Incomplete notes, body-camera angles that do not capture the eyes, or poor descriptions of timing and technique can undermine reliability.
Practical Takeaways
- For law enforcement: Careful adherence to standardized HGN methods, clear instructions, proper timing, and thorough documentation are essential. HGN should be used with other observations and tests.
- For drivers and counsel: The reliability of HGN depends on correct administration and the absence of other medical or environmental causes. In Ohio, challenging HGN often focuses on whether the officer substantially complied with standardized procedures and whether conditions or health factors could explain the observed eye movements.
Conclusion
The HGN test is a common tool to help assess possible alcohol impairment. In Ohio, its value in court depends on whether the officer substantially complied with standardized procedures and properly documented the process. Although many agencies rely on HGN, it has recognized limits, and both medical and legal sources have raised valid concerns about alternative causes, administration errors, and overreliance. Courts typically view HGN as one piece of the larger impairment picture, to be weighed alongside all other evidence.