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Challenging the Horizontal Gaze Nystagmus Test: A Closer Look

by | Oct 31, 2023 | DWI |

DWI charges carry severe consequences, affecting multiple aspects of your life. If you’re charged with DWI in Louisiana, understanding the legal process and mounting an effective defense is crucial. One commonly used field sobriety test is the Horizontal Gaze Nystagmus (HGN) test, which measures involuntary eye movements that may indicate intoxication. However, it’s important to note that this test is not foolproof and can be challenged by experienced DWI attorneys. In this blog post, we’ll explore how defense attorneys challenge the HGN test and why seeking legal representation is imperative if you’re facing a DWI charge in Louisiana.

Understanding the Horizontal Gaze Nystagmus Test

Before delving into the ways in which criminal defense attorneys challenge the HGN test, it is crucial to understand what this test entails. The HGN test involves an officer observing a person’s eyes as they follow a moving object horizontally. The officer looks for three specific indicators:

  1. Lack of Smooth Pursuit: When an individual’s eyes cannot smoothly follow a moving object and instead display jerking or bouncing movement.
  2. Distinct Nystagmus at Maximum Deviation: When there is an involuntary jerking of the eyeball when looking fully to either side.
  3. Onset of Nystagmus Prior to 45 Degrees: When nystagmus occurs before the eyes reach a 45-degree angle from center.

Based on these observations, law enforcement officers make subjective judgments about whether someone may be intoxicated.

Horizontal Gaze Nystagmus Test by Officer

Challenging Field Sobriety Tests as a Defense Strategy

Field sobriety tests like the HGN are commonly used as evidence against individuals accused of driving while intoxicated. However, these tests are not flawless and can be challenged by skilled criminal defense attorneys. Here are some common strategies employed to challenge the HGN test:

Lack of Proper Administration

To ensure accurate results, the HGN test must be administered correctly. Improper administration can lead to false positives or unreliable results. Criminal defense attorneys carefully examine whether the officer followed proper protocol during the test, including factors such as:

  • Was there adequate lighting for proper observation?
  • Were the instructions provided by the officer clear and understandable?
  • Was there any distracting background noise that could have affected the individual’s performance?

By pinpointing any deviations from standard procedure, defense attorneys can weaken the credibility of the test results.

Officer Inexperience or Lack of Training

The accuracy of field sobriety tests depends on the expertise and training of law enforcement officers. Errors can occur if officers lack experience or sufficient training in conducting and interpreting the tests. Skilled DWI attorneys investigate whether officers had the necessary qualifications to conduct HGN tests. If officers lacked appropriate training and experience, it raises doubts about their ability to assess intoxication accurately.

Certain medical conditions or external factors unrelated to alcohol consumption can affect performance on field sobriety tests, including the HGN test. Factors like eye conditions, inner ear problems, prescription medications, or fatigue may contribute to abnormal eye movements. Defense attorneys explore these possibilities to challenge the accuracy and reliability of HGN test results in court.

Challenging HGN Test Results: A Complex Endeavor

Successfully challenging HGN test results requires a thorough understanding of scientific principles and legal precedents. DWI defense attorneys specialize in these complex matters and know how to effectively leverage their expertise. By skillfully questioning the validity and interpretation of field sobriety tests, including the HGN test, they can create reasonable doubt and strengthen your defense.  If you have a DWI and want an experienced attorney to review your case call today for a free consultation at 504-434-7000.