The Horizontal Gaze Nystagmus (HGN) test is a standardized field sobriety test (FST) used by law enforcement officers to assess a driver's level of intoxication. It involves observing the involuntary jerking of the eyes (nystagmus) as the suspect follows a moving stimulus, typically a penlight. However, the technique of how the light is used is crucial, and improper administration can lead to inaccurate results and legal challenges. This post will explore the correct procedure, potential issues with flashing the light, and the overall importance of proper testing.
What is the Horizontal Gaze Nystagmus (HGN) Test?
The HGN test is based on the principle that alcohol and other intoxicating substances affect the nervous system, causing the eyes to exhibit involuntary jerking movements. The officer observes three key indicators:
- Lack of Smooth Pursuit: As the suspect follows the stimulus, the officer checks for smooth, continuous eye movement. Jerky or interrupted movement suggests impairment.
- Distinct Nystagmus at Maximum Deviation: When the eye is looking as far as it can to the side, the officer looks for jerking. The presence of nystagmus at this point is a strong indicator of impairment.
- Onset of Nystagmus Prior to 45 Degrees: Nystagmus beginning before the eye reaches a 45-degree angle of deviation also suggests impairment.
Why Flashing the Light Can Be Problematic
Flashing the light directly into the subject's eye is generally considered improper technique and can compromise the test's validity. Here's why:
- Distraction and Irritation: Rapid flashing can be distracting and irritating, causing involuntary eye movements unrelated to intoxication. This could lead to a false positive result.
- Obscuring Subtle Nystagmus: The quick flashes might actually mask subtle nystagmus, leading to a false negative result. The officer needs to observe continuous, smooth movement, and rapid flashing prevents that observation.
- Legal Challenges: Improper administration of the HGN test, including flashing the light, can be grounds for legal challenges to the test's admissibility in court. Defense attorneys often argue that improper technique invalidates the test results.
How Should the Light Be Used in the HGN Test?
The light should be held steadily, approximately 12-15 inches from the subject's eye, and moved slowly and smoothly in a horizontal arc. The officer should avoid flashing the light. The focus is on observing the smoothness of the eye movement, not on creating any additional eye movement through the manipulation of the light source.
What if the Suspect Has a Pre-Existing Eye Condition?
H2: Can Pre-Existing Eye Conditions Affect the HGN Test?
Yes, pre-existing eye conditions or injuries can significantly affect the results of an HGN test. Conditions like nystagmus, strabismus, or other neurological disorders can cause involuntary eye movements independent of alcohol or drug consumption. It's crucial for the officer to be aware of any reported medical conditions and to consider these factors when interpreting the results. Ideally, a suspect should disclose any such conditions before the test begins.
What is the Accuracy of the HGN Test?
H2: How Accurate is the HGN Test on its Own?
The HGN test is not a stand-alone test for determining intoxication. It's just one component of a battery of field sobriety tests. While studies show a correlation between positive HGN results and alcohol impairment, it's not foolproof. Factors like fatigue, medication, or other medical conditions can also influence the results. The HGN test is most reliable when used in conjunction with other tests like the one-leg stand and walk-and-turn tests.
Can I Refuse the HGN Test?
H2: Can I Refuse to Take the HGN Test?
In most jurisdictions, refusing to take field sobriety tests, including the HGN, can be considered evidence of guilt. The consequences of refusal are often similar to those of a positive test result. It's best to consult with an attorney if you're unsure about your rights and obligations during a DUI stop.
In conclusion, the proper administration of the HGN test is paramount. Flashing the light is an improper technique that can lead to inaccurate results and legal challenges. The test should be conducted by trained officers who understand the correct procedure and interpret the results in conjunction with other field sobriety tests and evidence. Understanding this process is crucial for both law enforcement and individuals who may find themselves undergoing this test.
