Understanding the Role of the Horizontal Gaze Nystagmus Test (the “eye test”) in DWI and DUI Investigations

Understanding the Role of the Horizontal Gaze Nystagmus Test (the “eye test”) in DWI and DUI Investigations

If you are stopped in Houston or anywhere in Texas and suspected of DWI or DUI, it is likely that the officer will administer Standardized Field Sobriety Tests (SFSTs), in order to assess your level of impairment. Although criminal defense lawyers understand that SFSTs are poor indicators of impairment, they are nevertheless a central part of DWI or DUI investigations. If you perform poorly on the tests, the officer may develop the probable cause needed to arrest you.

The first test administered by police officers is usually the horizontal gaze nystagmus test (“HGN” – also referred to as the “eye test”). According manuals put out by the National Highway Transportation Safety Administration (“NHTSA”), “nystagmus is defined as involuntary jerking of the eyes. Alcohol and certain other drugs cause Horizontal Gaze Nystagmus.”

As the name of the test implies, Horizontal Gaze Nystagmus occurs as the eyes move to the side. Manuals put out by NHTSA claim – and this is disputed by criminal defense lawyers in Houston and everywhere –  that HGN provides the “first and most accurate test in the Standardized Field Sobriety Test battery.”

An officer who administers HGN will usually ask a DWI or DUI suspect to keep his head still and follow a pen, light or even a finger. According to the detailed instructions in the NHTSA manual, the officer should check each eye individually and make several passes.

In DWI or DUI  investigations, experienced criminal defense attorney know that there are three “clues” that HGN is present in a suspect: lack of smooth pursuit, distinct and sustained nystagmus at maximum deviation, and onset of nystagmus prior to 45 degrees. According to the manual, the “higher the degree of impairment, the sooner nystagmus will be observable.”

Our Houston DWI lawyers know that the test must be performed in strict compliance with the guidelines set out by NHTSA – otherwise it is an even poorer indicator of sobriety and may not even be admissible in court. The manual specifies in detail how the test should be administered, and an experienced DWI lawyer in Houston should be familiar with the guidelines. Because the test is “standardized,” it should be administered the same each time in and DWI investigation, whether it be in Houston, Galveston, Conroe, or anywhere in Texas or the United States.

Although many people understand that they have the right to refuse a breath or blood test, they do not know that they can also refuse to participate in SFSTs. Although criminal defense attorneys know there are risks to not participating in SFSTs (in many cases, for example, the officer will think you are drunk and will arrest you), it may be the wise approach in many cases. If you refuse to participate in SFSTs, you should always do so politely and in a clear voice.