The Horizontal Gaze Nystagmus (HGN) test is a standardized field sobriety test (SFST) frequently used by law enforcement officers to assess the potential impairment of a driver suspected of driving under the influence (DUI) of alcohol or drugs. While the test itself is relatively straightforward, questions often arise concerning specific aspects of its execution, particularly regarding the use of a light source. This article will delve into the proper procedures for administering the HGN test, address concerns about flashing a light in someone's eyes, and discuss potential complications.
What is the Horizontal Gaze Nystagmus (HGN) Test?
The HGN test focuses on involuntary jerking movements of the eyes (nystagmus) as they track a moving stimulus, typically a penlight or similar object. The officer moves the stimulus smoothly horizontally, asking the suspect to follow it with their eyes only, without moving their head. The presence of nystagmus, specifically its onset before 45 degrees of lateral gaze, its distinctness, and its inability to be overcome by the suspect, are indicators of potential impairment.
Why is a Light Used in the HGN Test?
A penlight or similar light source is used primarily to provide a clear and easily followed target for the suspect's eyes. The consistent movement of the light ensures that the officer can accurately observe any involuntary jerking or wavering of the eyes, which is crucial for diagnosing the presence and intensity of nystagmus. The light's brightness helps the officer to clearly see the eye movements, even in less-than-ideal lighting conditions.
Is Flashing the Light Harmful?
The light used in the HGN test is not intended to be flashed. The stimulus should be moved in a smooth, continuous motion. Flashing the light could be considered improper procedure and might affect the accuracy and reliability of the test results. Sudden bright flashes can cause temporary visual disturbances and discomfort, potentially interfering with the suspect's ability to accurately follow the stimulus. This could lead to inaccurate observations and a potentially flawed interpretation of the test.
How Should the Light Be Used Correctly?
A properly administered HGN test requires a steady, smooth movement of the light. The light should be held at a distance of approximately 12-15 inches from the suspect's face, and moved horizontally at a speed that allows the suspect to comfortably track it. The movement should be smooth and consistent, avoiding jerky motions or sudden stops. The officer should carefully observe the suspect's eyes for any signs of nystagmus throughout the entire process.
What if the Suspect Complains of Discomfort or Difficulty?
If the suspect complains of discomfort or difficulty during the HGN test, the officer should take this into account and consider whether the test is being administered correctly. It's important to remember that the HGN test is only one part of a broader DUI investigation, and other factors should be considered before making any conclusions about impairment. Discomfort or difficulty could indicate an issue with the test procedure, underlying medical conditions, or other factors unrelated to impairment.
Can Medical Conditions Affect HGN Test Results?
Yes, certain medical conditions can affect the results of an HGN test. For instance, neurological conditions, inner ear problems, or even eye strain can cause nystagmus, potentially leading to a false positive. This is why it's crucial to interpret the HGN test results within the context of the entire DUI investigation, considering other factors such as the suspect's behavior, statements, and the results of other field sobriety tests.
What are the Other Field Sobriety Tests Used with HGN?
The HGN test is often administered in conjunction with other field sobriety tests, including the Walk-and-Turn test and the One-Leg Stand test. These tests provide a more comprehensive assessment of the suspect's coordination, balance, and cognitive abilities. The combined results of all three tests help officers build a more complete picture of the suspect's level of impairment.
In conclusion, while a light source is an essential component of the HGN test, it should be used correctly. Flashing the light is improper procedure and may compromise the accuracy of the test. Understanding the proper administration of the test and considering the possibility of medical conditions or other contributing factors are crucial in ensuring accurate and fair assessments of impairment.
